scsi: docs: convert scsi_mid_low_api.txt to ReST

Mauro Carvalho Chehab committed 6 years ago

Commit ce5c5d61 parent d4d79345 files · +1337 −1282Browse files

Unified · Split

5 files

Documentation/scsi/index.rst +1 −0
Documentation/scsi/scsi_eh.rst +1 −1
Documentation/scsi/scsi_mid_low_api.rst +1334 −0
Documentation/scsi/scsi_mid_low_api.txt +0 −1280
scripts/documentation-file-ref-check +1 −1

@@ -35,5 +35,6 @@ Linux SCSI Subsystem · 34 unmodified lines
35	scsi_eh	35	scsi_eh
36	scsi_fc_transport	36	scsi_fc_transport
37	scsi-generic	37	scsi-generic
		38	scsi_mid_low_api
38		39
39	scsi_transport_srp/figures	40	scsi_transport_srp/figures

Documentation/scsi/scsi_eh.rst+1−1

@@ -5,7 +5,7 @@ SCSI EH · 4 unmodified lines
5	=======	5	=======
6		6
7	This document describes SCSI midlayer error handling infrastructure.	7	This document describes SCSI midlayer error handling infrastructure.
8	Please refer to Documentation/scsi/scsi_mid_low_api.txt for more	8	Please refer to Documentation/scsi/scsi_mid_low_api.rst for more
9	information regarding SCSI midlayer.	9	information regarding SCSI midlayer.
10		10
11	.. TABLE OF CONTENTS	11	.. TABLE OF CONTENTS

Documentation/scsi/scsi_mid_low_api.rst+1334−0

@@ -0,0 +1,1334 @@
	1	.. SPDX-License-Identifier: GPL-2.0
	2
	3	=============================================
	4	SCSI mid_level - lower_level driver interface
	5	=============================================
	6
	7	Introduction
	8	============
	9	This document outlines the interface between the Linux SCSI mid level and
	10	SCSI lower level drivers. Lower level drivers (LLDs) are variously called
	11	host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
	12	context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
	13	single SCSI initiator port on a SCSI transport. An "initiator" port
	14	(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
	15	to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
	16	system, but only one per hardware type. Most LLDs can control one or more
	17	SCSI HBAs. Some HBAs contain multiple hosts.
	18
	19	In some cases the SCSI transport is an external bus that already has
	20	its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
	21	SCSI subsystem LLD is a software bridge to the other driver subsystem.
	22	Examples are the usb-storage driver (found in the drivers/usb/storage
	23	directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
	24	directory).
	25
	26	For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
	27	(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
	28	LLD can be built into the kernel or loaded as a module. There can only be
	29	one aic7xxx LLD running in a Linux system but it may be controlling many
	30	HBAs. These HBAs might be either on PCI daughter-boards or built into
	31	the motherboard (or both). Some aic7xxx based HBAs are dual controllers
	32	and thus represent two hosts. Like most modern HBAs, each aic7xxx host
	33	has its own PCI device address. [The one-to-one correspondence between
	34	a SCSI host and a PCI device is common but not required (e.g. with
	35	ISA adapters).]
	36
	37	The SCSI mid level isolates an LLD from other layers such as the SCSI
	38	upper layer drivers and the block layer.
	39
	40	This version of the document roughly matches linux kernel version 2.6.8 .
	41
	42	Documentation
	43	=============
	44	There is a SCSI documentation directory within the kernel source tree,
	45	typically Documentation/scsi . Most documents are in plain
	46	(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
	47	found in that directory. A more recent copy of this document may be found
	48	at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
	49	Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
	50	briefly described in scsi.txt which contains a url to a document
	51	describing the SCSI subsystem in the lk 2.4 series. Two upper level
	52	drivers have documents in that directory: st.txt (SCSI tape driver) and
	53	scsi-generic.txt (for the sg driver).
	54
	55	Some documentation (or urls) for LLDs may be found in the C source code
	56	or in the same directory as the C source code. For example to find a url
	57	about the USB mass storage driver see the
	58	/usr/src/linux/drivers/usb/storage directory.
	59
	60	Driver structure
	61	================
	62	Traditionally an LLD for the SCSI subsystem has been at least two files in
	63	the drivers/scsi directory. For example, a driver called "xyz" has a header
	64	file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
	65	why this couldn't all be in one file; the header file is superfluous.] Some
	66	drivers that have been ported to several operating systems have more than
	67	two files. For example the aic7xxx driver has separate files for generic
	68	and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
	69	their own directory under the drivers/scsi directory.
	70
	71	When a new LLD is being added to Linux, the following files (found in the
	72	drivers/scsi directory) will need some attention: Makefile and Kconfig .
	73	It is probably best to study how existing LLDs are organized.
	74
	75	As the 2.5 series development kernels evolve into the 2.6 series
	76	production series, changes are being introduced into this interface. An
	77	example of this is driver initialization code where there are now 2 models
	78	available. The older one, similar to what was found in the lk 2.4 series,
	79	is based on hosts that are detected at HBA driver load time. This will be
	80	referred to the "passive" initialization model. The newer model allows HBAs
	81	to be hot plugged (and unplugged) during the lifetime of the LLD and will
	82	be referred to as the "hotplug" initialization model. The newer model is
	83	preferred as it can handle both traditional SCSI equipment that is
	84	permanently connected as well as modern "SCSI" devices (e.g. USB or
	85	IEEE 1394 connected digital cameras) that are hotplugged. Both
	86	initialization models are discussed in the following sections.
	87
	88	An LLD interfaces to the SCSI subsystem several ways:
	89
	90	a) directly invoking functions supplied by the mid level
	91	b) passing a set of function pointers to a registration function
	92	supplied by the mid level. The mid level will then invoke these
	93	functions at some point in the future. The LLD will supply
	94	implementations of these functions.
	95	c) direct access to instances of well known data structures maintained
	96	by the mid level
	97
	98	Those functions in group a) are listed in a section entitled "Mid level
	99	supplied functions" below.
	100
	101	Those functions in group b) are listed in a section entitled "Interface
	102	functions" below. Their function pointers are placed in the members of
	103	"struct scsi_host_template", an instance of which is passed to
	104	scsi_host_alloc() [#]_. Those interface functions that the LLD does not
	105	wish to supply should have NULL placed in the corresponding member of
	106	struct scsi_host_template. Defining an instance of struct
	107	scsi_host_template at file scope will cause NULL to be placed in function
	108	pointer members not explicitly initialized.
	109
	110	Those usages in group c) should be handled with care, especially in a
	111	"hotplug" environment. LLDs should be aware of the lifetime of instances
	112	that are shared with the mid level and other layers.
	113
	114	All functions defined within an LLD and all data defined at file scope
	115	should be static. For example the slave_alloc() function in an LLD
	116	called "xxx" could be defined as
	117	``static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }``
	118
	119	.. [#] the scsi_host_alloc() function is a replacement for the rather vaguely
	120	named scsi_register() function in most situations.
	121
	122
	123	Hotplug initialization model
	124	============================
	125	In this model an LLD controls when SCSI hosts are introduced and removed
	126	from the SCSI subsystem. Hosts can be introduced as early as driver
	127	initialization and removed as late as driver shutdown. Typically a driver
	128	will respond to a sysfs probe() callback that indicates an HBA has been
	129	detected. After confirming that the new device is one that the LLD wants
	130	to control, the LLD will initialize the HBA and then register a new host
	131	with the SCSI mid level.
	132
	133	During LLD initialization the driver should register itself with the
	134	appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
	135	This can probably be done via sysfs. Any driver parameters (especially
	136	those that are writable after the driver is loaded) could also be
	137	registered with sysfs at this point. The SCSI mid level first becomes
	138	aware of an LLD when that LLD registers its first HBA.
	139
	140	At some later time, the LLD becomes aware of an HBA and what follows
	141	is a typical sequence of calls between the LLD and the mid level.
	142	This example shows the mid level scanning the newly introduced HBA for 3
	143	scsi devices of which only the first 2 respond::
	144
	145	HBA PROBE: assume 2 SCSI devices found in scan
	146	LLD mid level LLD
	147	===-------------------=========--------------------===------
	148	scsi_host_alloc() -->
	149	scsi_add_host() ---->
	150	scsi_scan_host() -------+
	151	\|
	152	slave_alloc()
	153	slave_configure() --> scsi_change_queue_depth()
	154	\|
	155	slave_alloc()
	156	slave_configure()
	157	\|
	158	slave_alloc() ***
	159	slave_destroy() ***
	160
	161
	162	*** For scsi devices that the mid level tries to scan but do not
	163	respond, a slave_alloc(), slave_destroy() pair is called.
	164
	165	If the LLD wants to adjust the default queue settings, it can invoke
	166	scsi_change_queue_depth() in its slave_configure() routine.
	167
	168	When an HBA is being removed it could be as part of an orderly shutdown
	169	associated with the LLD module being unloaded (e.g. with the "rmmod"
	170	command) or in response to a "hot unplug" indicated by sysfs()'s
	171	remove() callback being invoked. In either case, the sequence is the
	172	same::
	173
	174	HBA REMOVE: assume 2 SCSI devices attached
	175	LLD mid level LLD
	176	===----------------------=========-----------------===------
	177	scsi_remove_host() ---------+
	178	\|
	179	slave_destroy()
	180	slave_destroy()
	181	scsi_host_put()
	182
	183	It may be useful for a LLD to keep track of struct Scsi_Host instances
	184	(a pointer is returned by scsi_host_alloc()). Such instances are "owned"
	185	by the mid-level. struct Scsi_Host instances are freed from
	186	scsi_host_put() when the reference count hits zero.
	187
	188	Hot unplugging an HBA that controls a disk which is processing SCSI
	189	commands on a mounted file system is an interesting situation. Reference
	190	counting logic is being introduced into the mid level to cope with many
	191	of the issues involved. See the section on reference counting below.
	192
	193
	194	The hotplug concept may be extended to SCSI devices. Currently, when an
	195	HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
	196	attached to the HBA's SCSI transport. On newer SCSI transports the HBA
	197	may become aware of a new SCSI device _after_ the scan has completed.
	198	An LLD can use this sequence to make the mid level aware of a SCSI device::
	199
	200	SCSI DEVICE hotplug
	201	LLD mid level LLD
	202	===-------------------=========--------------------===------
	203	scsi_add_device() ------+
	204	\|
	205	slave_alloc()
	206	slave_configure() [--> scsi_change_queue_depth()]
	207
	208	In a similar fashion, an LLD may become aware that a SCSI device has been
	209	removed (unplugged) or the connection to it has been interrupted. Some
	210	existing SCSI transports (e.g. SPI) may not become aware that a SCSI
	211	device has been removed until a subsequent SCSI command fails which will
	212	probably cause that device to be set offline by the mid level. An LLD that
	213	detects the removal of a SCSI device can instigate its removal from
	214	upper layers with this sequence::
	215
	216	SCSI DEVICE hot unplug
	217	LLD mid level LLD
	218	===----------------------=========-----------------===------
	219	scsi_remove_device() -------+
	220	\|
	221	slave_destroy()
	222
	223	It may be useful for an LLD to keep track of struct scsi_device instances
	224	(a pointer is passed as the parameter to slave_alloc() and
	225	slave_configure() callbacks). Such instances are "owned" by the mid-level.
	226	struct scsi_device instances are freed after slave_destroy().
	227
	228
	229	Reference Counting
	230	==================
	231	The Scsi_Host structure has had reference counting infrastructure added.
	232	This effectively spreads the ownership of struct Scsi_Host instances
	233	across the various SCSI layers which use them. Previously such instances
	234	were exclusively owned by the mid level. LLDs would not usually need to
	235	directly manipulate these reference counts but there may be some cases
	236	where they do.
	237
	238	There are 3 reference counting functions of interest associated with
	239	struct Scsi_Host:
	240
	241	- scsi_host_alloc():
	242	returns a pointer to new instance of struct
	243	Scsi_Host which has its reference count ^^ set to 1
	244
	245	- scsi_host_get():
	246	adds 1 to the reference count of the given instance
	247
	248	- scsi_host_put():
	249	decrements 1 from the reference count of the given
	250	instance. If the reference count reaches 0 then the given instance
	251	is freed
	252
	253	The scsi_device structure has had reference counting infrastructure added.
	254	This effectively spreads the ownership of struct scsi_device instances
	255	across the various SCSI layers which use them. Previously such instances
	256	were exclusively owned by the mid level. See the access functions declared
	257	towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
	258	a copy of a pointer to a scsi_device instance it should use scsi_device_get()
	259	to bump its reference count. When it is finished with the pointer it can
	260	use scsi_device_put() to decrement its reference count (and potentially
	261	delete it).
	262
	263	.. Note::
	264
	265	struct Scsi_Host actually has 2 reference counts which are manipulated
	266	in parallel by these functions.
	267
	268
	269	Conventions
	270	===========
	271	First, Linus Torvalds's thoughts on C coding style can be found in the
	272	Documentation/process/coding-style.rst file.
	273
	274	Next, there is a movement to "outlaw" typedefs introducing synonyms for
	275	struct tags. Both can be still found in the SCSI subsystem, but
	276	the typedefs have been moved to a single file, scsi_typedefs.h to
	277	make their future removal easier, for example:
	278	"typedef struct scsi_cmnd Scsi_Cmnd;"
	279
	280	Also, most C99 enhancements are encouraged to the extent they are supported
	281	by the relevant gcc compilers. So C99 style structure and array
	282	initializers are encouraged where appropriate. Don't go too far,
	283	VLAs are not properly supported yet. An exception to this is the use of
	284	``//`` style comments; ``/.../`` comments are still preferred in Linux.
	285
	286	Well written, tested and documented code, need not be re-formatted to
	287	comply with the above conventions. For example, the aic7xxx driver
	288	comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
	289	and Adaptec have their own coding conventions.
	290
	291
	292	Mid level supplied functions
	293	============================
	294	These functions are supplied by the SCSI mid level for use by LLDs.
	295	The names (i.e. entry points) of these functions are exported
	296	so an LLD that is a module can access them. The kernel will
	297	arrange for the SCSI mid level to be loaded and initialized before any LLD
	298	is initialized. The functions below are listed alphabetically and their
	299	names all start with ``scsi_``.
	300
	301	Summary:
	302
	303	- scsi_add_device - creates new scsi device (lu) instance
	304	- scsi_add_host - perform sysfs registration and set up transport class
	305	- scsi_change_queue_depth - change the queue depth on a SCSI device
	306	- scsi_bios_ptable - return copy of block device's partition table
	307	- scsi_block_requests - prevent further commands being queued to given host
	308	- scsi_host_alloc - return a new scsi_host instance whose refcount==1
	309	- scsi_host_get - increments Scsi_Host instance's refcount
	310	- scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
	311	- scsi_partsize - parse partition table into cylinders, heads + sectors
	312	- scsi_register - create and register a scsi host adapter instance.
	313	- scsi_remove_device - detach and remove a SCSI device
	314	- scsi_remove_host - detach and remove all SCSI devices owned by host
	315	- scsi_report_bus_reset - report scsi _bus_ reset observed
	316	- scsi_scan_host - scan SCSI bus
	317	- scsi_track_queue_full - track successive QUEUE_FULL events
	318	- scsi_unblock_requests - allow further commands to be queued to given host
	319	- scsi_unregister - [calls scsi_host_put()]
	320
	321
	322	Details::
	323
	324	/**
	325	* scsi_add_device - creates new scsi device (lu) instance
	326	* @shost: pointer to scsi host instance
	327	* @channel: channel number (rarely other than 0)
	328	* @id: target id number
	329	* @lun: logical unit number
	330	*
	331	* Returns pointer to new struct scsi_device instance or
	332	* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
	333	* wrong (e.g. no lu responds at given address)
	334	*
	335	* Might block: yes
	336	*
	337	* Notes: This call is usually performed internally during a scsi
	338	* bus scan when an HBA is added (i.e. scsi_scan_host()). So it
	339	* should only be called if the HBA becomes aware of a new scsi
	340	* device (lu) after scsi_scan_host() has completed. If successful
	341	* this call can lead to slave_alloc() and slave_configure() callbacks
	342	* into the LLD.
	343	*
	344	* Defined in: drivers/scsi/scsi_scan.c
	345	**/
	346	struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
	347	unsigned int channel,
	348	unsigned int id, unsigned int lun)
	349
	350
	351	/**
	352	* scsi_add_host - perform sysfs registration and set up transport class
	353	* @shost: pointer to scsi host instance
	354	* @dev: pointer to struct device of type scsi class
	355	*
	356	* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
	357	*
	358	* Might block: no
	359	*
	360	* Notes: Only required in "hotplug initialization model" after a
	361	* successful call to scsi_host_alloc(). This function does not
	362	* scan the bus; this can be done by calling scsi_scan_host() or
	363	* in some other transport-specific way. The LLD must set up
	364	* the transport template before calling this function and may only
	365	* access the transport class data after this function has been called.
	366	*
	367	* Defined in: drivers/scsi/hosts.c
	368	**/
	369	int scsi_add_host(struct Scsi_Host shost, struct device dev)
	370
	371
	372	/**
	373	* scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
	374	* @sdev: pointer to SCSI device to change queue depth on
	375	* @tags Number of tags allowed if tagged queuing enabled,
	376	* or number of commands the LLD can queue up
	377	* in non-tagged mode (as per cmd_per_lun).
	378	*
	379	* Returns nothing
	380	*
	381	* Might block: no
	382	*
	383	* Notes: Can be invoked any time on a SCSI device controlled by this
	384	* LLD. [Specifically during and after slave_configure() and prior to
	385	* slave_destroy().] Can safely be invoked from interrupt code.
	386	*
	387	* Defined in: drivers/scsi/scsi.c [see source code for more notes]
	388	*
	389	**/
	390	int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
	391
	392
	393	/**
	394	* scsi_bios_ptable - return copy of block device's partition table
	395	* @dev: pointer to block device
	396	*
	397	* Returns pointer to partition table, or NULL for failure
	398	*
	399	* Might block: yes
	400	*
	401	* Notes: Caller owns memory returned (free with kfree() )
	402	*
	403	* Defined in: drivers/scsi/scsicam.c
	404	**/
	405	unsigned char scsi_bios_ptable(struct block_device dev)
	406
	407
	408	/**
	409	* scsi_block_requests - prevent further commands being queued to given host
	410	*
	411	* @shost: pointer to host to block commands on
	412	*
	413	* Returns nothing
	414	*
	415	* Might block: no
	416	*
	417	* Notes: There is no timer nor any other means by which the requests
	418	* get unblocked other than the LLD calling scsi_unblock_requests().
	419	*
	420	* Defined in: drivers/scsi/scsi_lib.c
	421	**/
	422	void scsi_block_requests(struct Scsi_Host * shost)
	423
	424
	425	/**
	426	* scsi_host_alloc - create a scsi host adapter instance and perform basic
	427	* initialization.
	428	* @sht: pointer to scsi host template
	429	* @privsize: extra bytes to allocate in hostdata array (which is the
	430	* last member of the returned Scsi_Host instance)
	431	*
	432	* Returns pointer to new Scsi_Host instance or NULL on failure
	433	*
	434	* Might block: yes
	435	*
	436	* Notes: When this call returns to the LLD, the SCSI bus scan on
	437	* this host has _not_ yet been done.
	438	* The hostdata array (by default zero length) is a per host scratch
	439	* area for the LLD's exclusive use.
	440	* Both associated refcounting objects have their refcount set to 1.
	441	* Full registration (in sysfs) and a bus scan are performed later when
	442	* scsi_add_host() and scsi_scan_host() are called.
	443	*
	444	* Defined in: drivers/scsi/hosts.c .
	445	**/
	446	struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
	447	int privsize)
	448
	449
	450	/**
	451	* scsi_host_get - increment Scsi_Host instance refcount
	452	* @shost: pointer to struct Scsi_Host instance
	453	*
	454	* Returns nothing
	455	*
	456	* Might block: currently may block but may be changed to not block
	457	*
	458	* Notes: Actually increments the counts in two sub-objects
	459	*
	460	* Defined in: drivers/scsi/hosts.c
	461	**/
	462	void scsi_host_get(struct Scsi_Host *shost)
	463
	464
	465	/**
	466	* scsi_host_put - decrement Scsi_Host instance refcount, free if 0
	467	* @shost: pointer to struct Scsi_Host instance
	468	*
	469	* Returns nothing
	470	*
	471	* Might block: currently may block but may be changed to not block
	472	*
	473	* Notes: Actually decrements the counts in two sub-objects. If the
	474	* latter refcount reaches 0, the Scsi_Host instance is freed.
	475	* The LLD need not worry exactly when the Scsi_Host instance is
	476	* freed, it just shouldn't access the instance after it has balanced
	477	* out its refcount usage.
	478	*
	479	* Defined in: drivers/scsi/hosts.c
	480	**/
	481	void scsi_host_put(struct Scsi_Host *shost)
	482
	483
	484	/**
	485	* scsi_partsize - parse partition table into cylinders, heads + sectors
	486	* @buf: pointer to partition table
	487	* @capacity: size of (total) disk in 512 byte sectors
	488	* @cyls: outputs number of cylinders calculated via this pointer
	489	* @hds: outputs number of heads calculated via this pointer
	490	* @secs: outputs number of sectors calculated via this pointer
	491	*
	492	* Returns 0 on success, -1 on failure
	493	*
	494	* Might block: no
	495	*
	496	* Notes: Caller owns memory returned (free with kfree() )
	497	*
	498	* Defined in: drivers/scsi/scsicam.c
	499	**/
	500	int scsi_partsize(unsigned char *buf, unsigned long capacity,
	501	unsigned int cyls, unsigned int hds, unsigned int *secs)
	502
	503
	504	/**
	505	* scsi_register - create and register a scsi host adapter instance.
	506	* @sht: pointer to scsi host template
	507	* @privsize: extra bytes to allocate in hostdata array (which is the
	508	* last member of the returned Scsi_Host instance)
	509	*
	510	* Returns pointer to new Scsi_Host instance or NULL on failure
	511	*
	512	* Might block: yes
	513	*
	514	* Notes: When this call returns to the LLD, the SCSI bus scan on
	515	* this host has _not_ yet been done.
	516	* The hostdata array (by default zero length) is a per host scratch
	517	* area for the LLD.
	518	*
	519	* Defined in: drivers/scsi/hosts.c .
	520	**/
	521	struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
	522	int privsize)
	523
	524
	525	/**
	526	* scsi_remove_device - detach and remove a SCSI device
	527	* @sdev: a pointer to a scsi device instance
	528	*
	529	* Returns value: 0 on success, -EINVAL if device not attached
	530	*
	531	* Might block: yes
	532	*
	533	* Notes: If an LLD becomes aware that a scsi device (lu) has
	534	* been removed but its host is still present then it can request
	535	* the removal of that scsi device. If successful this call will
	536	* lead to the slave_destroy() callback being invoked. sdev is an
	537	* invalid pointer after this call.
	538	*
	539	* Defined in: drivers/scsi/scsi_sysfs.c .
	540	**/
	541	int scsi_remove_device(struct scsi_device *sdev)
	542
	543
	544	/**
	545	* scsi_remove_host - detach and remove all SCSI devices owned by host
	546	* @shost: a pointer to a scsi host instance
	547	*
	548	* Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
	549	*
	550	* Might block: yes
	551	*
	552	* Notes: Should only be invoked if the "hotplug initialization
	553	* model" is being used. It should be called _prior_ to
	554	* scsi_unregister().
	555	*
	556	* Defined in: drivers/scsi/hosts.c .
	557	**/
	558	int scsi_remove_host(struct Scsi_Host *shost)
	559
	560
	561	/**
	562	* scsi_report_bus_reset - report scsi _bus_ reset observed
	563	* @shost: a pointer to a scsi host involved
	564	* @channel: channel (within) host on which scsi bus reset occurred
	565	*
	566	* Returns nothing
	567	*
	568	* Might block: no
	569	*
	570	* Notes: This only needs to be called if the reset is one which
	571	* originates from an unknown location. Resets originated by the
	572	* mid level itself don't need to call this, but there should be
	573	* no harm. The main purpose of this is to make sure that a
	574	* CHECK_CONDITION is properly treated.
	575	*
	576	* Defined in: drivers/scsi/scsi_error.c .
	577	**/
	578	void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
	579
	580
	581	/**
	582	* scsi_scan_host - scan SCSI bus
	583	* @shost: a pointer to a scsi host instance
	584	*
	585	* Might block: yes
	586	*
	587	* Notes: Should be called after scsi_add_host()
	588	*
	589	* Defined in: drivers/scsi/scsi_scan.c
	590	**/
	591	void scsi_scan_host(struct Scsi_Host *shost)
	592
	593
	594	/**
	595	* scsi_track_queue_full - track successive QUEUE_FULL events on given
	596	* device to determine if and when there is a need
	597	* to adjust the queue depth on the device.
	598	* @sdev: pointer to SCSI device instance
	599	* @depth: Current number of outstanding SCSI commands on this device,
	600	* not counting the one returned as QUEUE_FULL.
	601	*
	602	* Returns 0 - no change needed
	603	* >0 - adjust queue depth to this new depth
	604	* -1 - drop back to untagged operation using host->cmd_per_lun
	605	* as the untagged command depth
	606	*
	607	* Might block: no
	608	*
	609	* Notes: LLDs may call this at any time and we will do "The Right
	610	* Thing"; interrupt context safe.
	611	*
	612	* Defined in: drivers/scsi/scsi.c .
	613	**/
	614	int scsi_track_queue_full(struct scsi_device *sdev, int depth)
	615
	616
	617	/**
	618	* scsi_unblock_requests - allow further commands to be queued to given host
	619	*
	620	* @shost: pointer to host to unblock commands on
	621	*
	622	* Returns nothing
	623	*
	624	* Might block: no
	625	*
	626	* Defined in: drivers/scsi/scsi_lib.c .
	627	**/
	628	void scsi_unblock_requests(struct Scsi_Host * shost)
	629
	630
	631	/**
	632	* scsi_unregister - unregister and free memory used by host instance
	633	* @shp: pointer to scsi host instance to unregister.
	634	*
	635	* Returns nothing
	636	*
	637	* Might block: no
	638	*
	639	* Notes: Should not be invoked if the "hotplug initialization
	640	* model" is being used. Called internally by exit_this_scsi_driver()
	641	* in the "passive initialization model". Hence a LLD has no need to
	642	* call this function directly.
	643	*
	644	* Defined in: drivers/scsi/hosts.c .
	645	**/
	646	void scsi_unregister(struct Scsi_Host * shp)
	647
	648
	649
	650
	651	Interface Functions
	652	===================
	653	Interface functions are supplied (defined) by LLDs and their function
	654	pointers are placed in an instance of struct scsi_host_template which
	655	is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
	656	Some are mandatory. Interface functions should be declared static. The
	657	accepted convention is that driver "xyz" will declare its slave_configure()
	658	function as::
	659
	660	static int xyz_slave_configure(struct scsi_device * sdev);
	661
	662	and so forth for all interface functions listed below.
	663
	664	A pointer to this function should be placed in the 'slave_configure' member
	665	of a "struct scsi_host_template" instance. A pointer to such an instance
	666	should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
	667	init_this_scsi_driver()].
	668
	669	The interface functions are also described in the include/scsi/scsi_host.h
	670	file immediately above their definition point in "struct scsi_host_template".
	671	In some cases more detail is given in scsi_host.h than below.
	672
	673	The interface functions are listed below in alphabetical order.
	674
	675	Summary:
	676
	677	- bios_param - fetch head, sector, cylinder info for a disk
	678	- eh_timed_out - notify the host that a command timer expired
	679	- eh_abort_handler - abort given command
	680	- eh_bus_reset_handler - issue SCSI bus reset
	681	- eh_device_reset_handler - issue SCSI device reset
	682	- eh_host_reset_handler - reset host (host bus adapter)
	683	- info - supply information about given host
	684	- ioctl - driver can respond to ioctls
	685	- proc_info - supports /proc/scsi/{driver_name}/{host_no}
	686	- queuecommand - queue scsi command, invoke 'done' on completion
	687	- slave_alloc - prior to any commands being sent to a new device
	688	- slave_configure - driver fine tuning for given device after attach
	689	- slave_destroy - given device is about to be shut down
	690
	691
	692	Details::
	693
	694	/**
	695	* bios_param - fetch head, sector, cylinder info for a disk
	696	* @sdev: pointer to scsi device context (defined in
	697	* include/scsi/scsi_device.h)
	698	* @bdev: pointer to block device context (defined in fs.h)
	699	* @capacity: device size (in 512 byte sectors)
	700	* @params: three element array to place output:
	701	* params[0] number of heads (max 255)
	702	* params[1] number of sectors (max 63)
	703	* params[2] number of cylinders
	704	*
	705	* Return value is ignored
	706	*
	707	* Locks: none
	708	*
	709	* Calling context: process (sd)
	710	*
	711	* Notes: an arbitrary geometry (based on READ CAPACITY) is used
	712	* if this function is not provided. The params array is
	713	* pre-initialized with made up values just in case this function
	714	* doesn't output anything.
	715	*
	716	* Optionally defined in: LLD
	717	**/
	718	int bios_param(struct scsi_device * sdev, struct block_device *bdev,
	719	sector_t capacity, int params[3])
	720
	721
	722	/**
	723	* eh_timed_out - The timer for the command has just fired
	724	* @scp: identifies command timing out
	725	*
	726	* Returns:
	727	*
	728	* EH_HANDLED: I fixed the error, please complete the command
	729	* EH_RESET_TIMER: I need more time, reset the timer and
	730	* begin counting again
	731	* EH_NOT_HANDLED Begin normal error recovery
	732	*
	733	*
	734	* Locks: None held
	735	*
	736	* Calling context: interrupt
	737	*
	738	* Notes: This is to give the LLD an opportunity to do local recovery.
	739	* This recovery is limited to determining if the outstanding command
	740	* will ever complete. You may not abort and restart the command from
	741	* this callback.
	742	*
	743	* Optionally defined in: LLD
	744	**/
	745	int eh_timed_out(struct scsi_cmnd * scp)
	746
	747
	748	/**
	749	* eh_abort_handler - abort command associated with scp
	750	* @scp: identifies command to be aborted
	751	*
	752	* Returns SUCCESS if command aborted else FAILED
	753	*
	754	* Locks: None held
	755	*
	756	* Calling context: kernel thread
	757	*
	758	* Notes: If 'no_async_abort' is defined this callback
	759	* will be invoked from scsi_eh thread. No other commands
	760	* will then be queued on current host during eh.
	761	* Otherwise it will be called whenever scsi_times_out()
	762	* is called due to a command timeout.
	763	*
	764	* Optionally defined in: LLD
	765	**/
	766	int eh_abort_handler(struct scsi_cmnd * scp)
	767
	768
	769	/**
	770	* eh_bus_reset_handler - issue SCSI bus reset
	771	* @scp: SCSI bus that contains this device should be reset
	772	*
	773	* Returns SUCCESS if command aborted else FAILED
	774	*
	775	* Locks: None held
	776	*
	777	* Calling context: kernel thread
	778	*
	779	* Notes: Invoked from scsi_eh thread. No other commands will be
	780	* queued on current host during eh.
	781	*
	782	* Optionally defined in: LLD
	783	**/
	784	int eh_bus_reset_handler(struct scsi_cmnd * scp)
	785
	786
	787	/**
	788	* eh_device_reset_handler - issue SCSI device reset
	789	* @scp: identifies SCSI device to be reset
	790	*
	791	* Returns SUCCESS if command aborted else FAILED
	792	*
	793	* Locks: None held
	794	*
	795	* Calling context: kernel thread
	796	*
	797	* Notes: Invoked from scsi_eh thread. No other commands will be
	798	* queued on current host during eh.
	799	*
	800	* Optionally defined in: LLD
	801	**/
	802	int eh_device_reset_handler(struct scsi_cmnd * scp)
	803
	804
	805	/**
	806	* eh_host_reset_handler - reset host (host bus adapter)
	807	* @scp: SCSI host that contains this device should be reset
	808	*
	809	* Returns SUCCESS if command aborted else FAILED
	810	*
	811	* Locks: None held
	812	*
	813	* Calling context: kernel thread
	814	*
	815	* Notes: Invoked from scsi_eh thread. No other commands will be
	816	* queued on current host during eh.
	817	* With the default eh_strategy in place, if none of the _abort_,
	818	* _device_reset_, _bus_reset_ or this eh handler function are
	819	* defined (or they all return FAILED) then the device in question
	820	* will be set offline whenever eh is invoked.
	821	*
	822	* Optionally defined in: LLD
	823	**/
	824	int eh_host_reset_handler(struct scsi_cmnd * scp)
	825
	826
	827	/**
	828	* info - supply information about given host: driver name plus data
	829	* to distinguish given host
	830	* @shp: host to supply information about
	831	*
	832	* Return ASCII null terminated string. [This driver is assumed to
	833	* manage the memory pointed to and maintain it, typically for the
	834	* lifetime of this host.]
	835	*
	836	* Locks: none
	837	*
	838	* Calling context: process
	839	*
	840	* Notes: Often supplies PCI or ISA information such as IO addresses
	841	* and interrupt numbers. If not supplied struct Scsi_Host::name used
	842	* instead. It is assumed the returned information fits on one line
	843	* (i.e. does not included embedded newlines).
	844	* The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
	845	* function (or struct Scsi_Host::name if this function is not
	846	* available).
	847	* In a similar manner, init_this_scsi_driver() outputs to the console
	848	* each host's "info" (or name) for the driver it is registering.
	849	* Also if proc_info() is not supplied, the output of this function
	850	* is used instead.
	851	*
	852	* Optionally defined in: LLD
	853	**/
	854	const char * info(struct Scsi_Host * shp)
	855
	856
	857	/**
	858	* ioctl - driver can respond to ioctls
	859	* @sdp: device that ioctl was issued for
	860	* @cmd: ioctl number
	861	* @arg: pointer to read or write data from. Since it points to
	862	* user space, should use appropriate kernel functions
	863	* (e.g. copy_from_user() ). In the Unix style this argument
	864	* can also be viewed as an unsigned long.
	865	*
	866	* Returns negative "errno" value when there is a problem. 0 or a
	867	* positive value indicates success and is returned to the user space.
	868	*
	869	* Locks: none
	870	*
	871	* Calling context: process
	872	*
	873	* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
	874	* The user issues an ioctl() against an upper level driver
	875	* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
	876	* the 'cmd' then it is passed to the SCSI mid level. If the SCSI
	877	* mid level does not recognize it, then the LLD that controls
	878	* the device receives the ioctl. According to recent Unix standards
	879	* unsupported ioctl() 'cmd' numbers should return -ENOTTY.
	880	*
	881	* Optionally defined in: LLD
	882	**/
	883	int ioctl(struct scsi_device sdp, int cmd, void arg)
	884
	885
	886	/**
	887	* proc_info - supports /proc/scsi/{driver_name}/{host_no}
	888	* @buffer: anchor point to output to (0==writeto1_read0) or fetch from
	889	* (1==writeto1_read0).
	890	* @start: where "interesting" data is written to. Ignored when
	891	* 1==writeto1_read0.
	892	* @offset: offset within buffer 0==writeto1_read0 is actually
	893	* interested in. Ignored when 1==writeto1_read0 .
	894	* @length: maximum (or actual) extent of buffer
	895	* @host_no: host number of interest (struct Scsi_Host::host_no)
	896	* @writeto1_read0: 1 -> data coming from user space towards driver
	897	* (e.g. "echo some_string > /proc/scsi/xyz/2")
	898	* 0 -> user what data from this driver
	899	* (e.g. "cat /proc/scsi/xyz/2")
	900	*
	901	* Returns length when 1==writeto1_read0. Otherwise number of chars
	902	* output to buffer past offset.
	903	*
	904	* Locks: none held
	905	*
	906	* Calling context: process
	907	*
	908	* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
	909	* support can now be configured out of the scsi subsystem.
	910	*
	911	* Optionally defined in: LLD
	912	**/
	913	int proc_info(char * buffer, char ** start, off_t offset,
	914	int length, int host_no, int writeto1_read0)
	915
	916
	917	/**
	918	* queuecommand - queue scsi command, invoke scp->scsi_done on completion
	919	* @shost: pointer to the scsi host object
	920	* @scp: pointer to scsi command object
	921	*
	922	* Returns 0 on success.
	923	*
	924	* If there's a failure, return either:
	925	*
	926	* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
	927	* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
	928	*
	929	* On both of these returns, the mid-layer will requeue the I/O
	930	*
	931	* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
	932	* device will be paused, and it will be unpaused when a command to
	933	* the device returns (or after a brief delay if there are no more
	934	* outstanding commands to it). Commands to other devices continue
	935	* to be processed normally.
	936	*
	937	* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
	938	* is paused and will be unpaused when any command returns from
	939	* the host (or after a brief delay if there are no outstanding
	940	* commands to the host).
	941	*
	942	* For compatibility with earlier versions of queuecommand, any
	943	* other return value is treated the same as
	944	* SCSI_MLQUEUE_HOST_BUSY.
	945	*
	946	* Other types of errors that are detected immediately may be
	947	* flagged by setting scp->result to an appropriate value,
	948	* invoking the scp->scsi_done callback, and then returning 0
	949	* from this function. If the command is not performed
	950	* immediately (and the LLD is starting (or will start) the given
	951	* command) then this function should place 0 in scp->result and
	952	* return 0.
	953	*
	954	* Command ownership. If the driver returns zero, it owns the
	955	* command and must take responsibility for ensuring the
	956	* scp->scsi_done callback is executed. Note: the driver may
	957	* call scp->scsi_done before returning zero, but after it has
	958	* called scp->scsi_done, it may not return any value other than
	959	* zero. If the driver makes a non-zero return, it must not
	960	* execute the command's scsi_done callback at any time.
	961	*
	962	* Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
	963	* held on entry (with "irqsave") and is expected to be
	964	* held on return. From 2.6.37 onwards, queuecommand is
	965	* called without any locks held.
	966	*
	967	* Calling context: in interrupt (soft irq) or process context
	968	*
	969	* Notes: This function should be relatively fast. Normally it
	970	* will not wait for IO to complete. Hence the scp->scsi_done
	971	* callback is invoked (often directly from an interrupt service
	972	* routine) some time after this function has returned. In some
	973	* cases (e.g. pseudo adapter drivers that manufacture the
	974	* response to a SCSI INQUIRY) the scp->scsi_done callback may be
	975	* invoked before this function returns. If the scp->scsi_done
	976	* callback is not invoked within a certain period the SCSI mid
	977	* level will commence error processing. If a status of CHECK
	978	* CONDITION is placed in "result" when the scp->scsi_done
	979	* callback is invoked, then the LLD driver should perform
	980	* autosense and fill in the struct scsi_cmnd::sense_buffer
	981	* array. The scsi_cmnd::sense_buffer array is zeroed prior to
	982	* the mid level queuing a command to an LLD.
	983	*
	984	* Defined in: LLD
	985	**/
	986	int queuecommand(struct Scsi_Host shost, struct scsi_cmnd scp)
	987
	988
	989	/**
	990	* slave_alloc - prior to any commands being sent to a new device
	991	* (i.e. just prior to scan) this call is made
	992	* @sdp: pointer to new device (about to be scanned)
	993	*
	994	* Returns 0 if ok. Any other return is assumed to be an error and
	995	* the device is ignored.
	996	*
	997	* Locks: none
	998	*
	999	* Calling context: process
	1000	*
	1001	* Notes: Allows the driver to allocate any resources for a device
	1002	* prior to its initial scan. The corresponding scsi device may not
	1003	* exist but the mid level is just about to scan for it (i.e. send
	1004	* and INQUIRY command plus ...). If a device is found then
	1005	* slave_configure() will be called while if a device is not found
	1006	* slave_destroy() is called.
	1007	* For more details see the include/scsi/scsi_host.h file.
	1008	*
	1009	* Optionally defined in: LLD
	1010	**/
	1011	int slave_alloc(struct scsi_device *sdp)
	1012
	1013
	1014	/**
	1015	* slave_configure - driver fine tuning for given device just after it
	1016	* has been first scanned (i.e. it responded to an
	1017	* INQUIRY)
	1018	* @sdp: device that has just been attached
	1019	*
	1020	* Returns 0 if ok. Any other return is assumed to be an error and
	1021	* the device is taken offline. [offline devices will _not_ have
	1022	* slave_destroy() called on them so clean up resources.]
	1023	*
	1024	* Locks: none
	1025	*
	1026	* Calling context: process
	1027	*
	1028	* Notes: Allows the driver to inspect the response to the initial
	1029	* INQUIRY done by the scanning code and take appropriate action.
	1030	* For more details see the include/scsi/scsi_host.h file.
	1031	*
	1032	* Optionally defined in: LLD
	1033	**/
	1034	int slave_configure(struct scsi_device *sdp)
	1035
	1036
	1037	/**
	1038	* slave_destroy - given device is about to be shut down. All
	1039	* activity has ceased on this device.
	1040	* @sdp: device that is about to be shut down
	1041	*
	1042	* Returns nothing
	1043	*
	1044	* Locks: none
	1045	*
	1046	* Calling context: process
	1047	*
	1048	* Notes: Mid level structures for given device are still in place
	1049	* but are about to be torn down. Any per device resources allocated
	1050	* by this driver for given device should be freed now. No further
	1051	* commands will be sent for this sdp instance. [However the device
	1052	* could be re-attached in the future in which case a new instance
	1053	* of struct scsi_device would be supplied by future slave_alloc()
	1054	* and slave_configure() calls.]
	1055	*
	1056	* Optionally defined in: LLD
	1057	**/
	1058	void slave_destroy(struct scsi_device *sdp)
	1059
	1060
	1061
	1062	Data Structures
	1063	===============
	1064	struct scsi_host_template
	1065	-------------------------
	1066	There is one "struct scsi_host_template" instance per LLD [#]_. It is
	1067	typically initialized as a file scope static in a driver's header file. That
	1068	way members that are not explicitly initialized will be set to 0 or NULL.
	1069	Member of interest:
	1070
	1071	name
	1072	- name of driver (may contain spaces, please limit to
	1073	less than 80 characters)
	1074
	1075	proc_name
	1076	- name used in "/proc/scsi/<proc_name>/<host_no>" and
	1077	by sysfs in one of its "drivers" directories. Hence
	1078	"proc_name" should only contain characters acceptable
	1079	to a Unix file name.
	1080
	1081	``(*queuecommand)()``
	1082	- primary callback that the mid level uses to inject
	1083	SCSI commands into an LLD.
	1084
	1085	The structure is defined and commented in include/scsi/scsi_host.h
	1086
	1087	.. [#] In extreme situations a single driver may have several instances
	1088	if it controls several different classes of hardware (e.g. an LLD
	1089	that handles both ISA and PCI cards and has a separate instance of
	1090	struct scsi_host_template for each class).
	1091
	1092	struct Scsi_Host
	1093	----------------
	1094	There is one struct Scsi_Host instance per host (HBA) that an LLD
	1095	controls. The struct Scsi_Host structure has many members in common
	1096	with "struct scsi_host_template". When a new struct Scsi_Host instance
	1097	is created (in scsi_host_alloc() in hosts.c) those common members are
	1098	initialized from the driver's struct scsi_host_template instance. Members
	1099	of interest:
	1100
	1101	host_no
	1102	- system wide unique number that is used for identifying
	1103	this host. Issued in ascending order from 0.
	1104	can_queue
	1105	- must be greater than 0; do not send more than can_queue
	1106	commands to the adapter.
	1107	this_id
	1108	- scsi id of host (scsi initiator) or -1 if not known
	1109	sg_tablesize
	1110	- maximum scatter gather elements allowed by host.
	1111	Set this to SG_ALL or less to avoid chained SG lists.
	1112	Must be at least 1.
	1113	max_sectors
	1114	- maximum number of sectors (usually 512 bytes) allowed
	1115	in a single SCSI command. The default value of 0 leads
	1116	to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
	1117	scsi_host.h) which is currently set to 1024. So for a
	1118	disk the maximum transfer size is 512 KB when max_sectors
	1119	is not defined. Note that this size may not be sufficient
	1120	for disk firmware uploads.
	1121	cmd_per_lun
	1122	- maximum number of commands that can be queued on devices
	1123	controlled by the host. Overridden by LLD calls to
	1124	scsi_change_queue_depth().
	1125	unchecked_isa_dma
	1126	- 1=>only use bottom 16 MB of ram (ISA DMA addressing
	1127	restriction), 0=>can use full 32 bit (or better) DMA
	1128	address space
	1129	no_async_abort
	1130	- 1=>Asynchronous aborts are not supported
	1131	- 0=>Timed-out commands will be aborted asynchronously
	1132	hostt
	1133	- pointer to driver's struct scsi_host_template from which
	1134	this struct Scsi_Host instance was spawned
	1135	hostt->proc_name
	1136	- name of LLD. This is the driver name that sysfs uses
	1137	transportt
	1138	- pointer to driver's struct scsi_transport_template instance
	1139	(if any). FC and SPI transports currently supported.
	1140	sh_list
	1141	- a double linked list of pointers to all struct Scsi_Host
	1142	instances (currently ordered by ascending host_no)
	1143	my_devices
	1144	- a double linked list of pointers to struct scsi_device
	1145	instances that belong to this host.
	1146	hostdata[0]
	1147	- area reserved for LLD at end of struct Scsi_Host. Size
	1148	is set by the second argument (named 'xtr_bytes') to
	1149	scsi_host_alloc() or scsi_register().
	1150	vendor_id
	1151	- a unique value that identifies the vendor supplying
	1152	the LLD for the Scsi_Host. Used most often in validating
	1153	vendor-specific message requests. Value consists of an
	1154	identifier type and a vendor-specific value.
	1155	See scsi_netlink.h for a description of valid formats.
	1156
	1157	The scsi_host structure is defined in include/scsi/scsi_host.h
	1158
	1159	struct scsi_device
	1160	------------------
	1161	Generally, there is one instance of this structure for each SCSI logical unit
	1162	on a host. Scsi devices connected to a host are uniquely identified by a
	1163	channel number, target id and logical unit number (lun).
	1164	The structure is defined in include/scsi/scsi_device.h
	1165
	1166	struct scsi_cmnd
	1167	----------------
	1168	Instances of this structure convey SCSI commands to the LLD and responses
	1169	back to the mid level. The SCSI mid level will ensure that no more SCSI
	1170	commands become queued against the LLD than are indicated by
	1171	scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
	1172	be at least one instance of struct scsi_cmnd available for each SCSI device.
	1173	Members of interest:
	1174
	1175	cmnd
	1176	- array containing SCSI command
	1177	cmnd_len
	1178	- length (in bytes) of SCSI command
	1179	sc_data_direction
	1180	- direction of data transfer in data phase. See
	1181	"enum dma_data_direction" in include/linux/dma-mapping.h
	1182	request_bufflen
	1183	- number of data bytes to transfer (0 if no data phase)
	1184	use_sg
	1185	- ==0 -> no scatter gather list, hence transfer data
	1186	to/from request_buffer
	1187	- >0 -> scatter gather list (actually an array) in
	1188	request_buffer with use_sg elements
	1189	request_buffer
	1190	- either contains data buffer or scatter gather list
	1191	depending on the setting of use_sg. Scatter gather
	1192	elements are defined by 'struct scatterlist' found
	1193	in include/linux/scatterlist.h .
	1194	done
	1195	- function pointer that should be invoked by LLD when the
	1196	SCSI command is completed (successfully or otherwise).
	1197	Should only be called by an LLD if the LLD has accepted
	1198	the command (i.e. queuecommand() returned or will return
	1199	0). The LLD may invoke 'done' prior to queuecommand()
	1200	finishing.
	1201	result
	1202	- should be set by LLD prior to calling 'done'. A value
	1203	of 0 implies a successfully completed command (and all
	1204	data (if any) has been transferred to or from the SCSI
	1205	target device). 'result' is a 32 bit unsigned integer that
	1206	can be viewed as 4 related bytes. The SCSI status value is
	1207	in the LSB. See include/scsi/scsi.h status_byte(),
	1208	msg_byte(), host_byte() and driver_byte() macros and
	1209	related constants.
	1210	sense_buffer
	1211	- an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
	1212	should be written when the SCSI status (LSB of 'result')
	1213	is set to CHECK_CONDITION (2). When CHECK_CONDITION is
	1214	set, if the top nibble of sense_buffer[0] has the value 7
	1215	then the mid level will assume the sense_buffer array
	1216	contains a valid SCSI sense buffer; otherwise the mid
	1217	level will issue a REQUEST_SENSE SCSI command to
	1218	retrieve the sense buffer. The latter strategy is error
	1219	prone in the presence of command queuing so the LLD should
	1220	always "auto-sense".
	1221	device
	1222	- pointer to scsi_device object that this command is
	1223	associated with.
	1224	resid
	1225	- an LLD should set this signed integer to the requested
	1226	transfer length (i.e. 'request_bufflen') less the number
	1227	of bytes that are actually transferred. 'resid' is
	1228	preset to 0 so an LLD can ignore it if it cannot detect
	1229	underruns (overruns should be rare). If possible an LLD
	1230	should set 'resid' prior to invoking 'done'. The most
	1231	interesting case is data transfers from a SCSI target
	1232	device (e.g. READs) that underrun.
	1233	underflow
	1234	- LLD should place (DID_ERROR << 16) in 'result' if
	1235	actual number of bytes transferred is less than this
	1236	figure. Not many LLDs implement this check and some that
	1237	do just output an error message to the log rather than
	1238	report a DID_ERROR. Better for an LLD to implement
	1239	'resid'.
	1240
	1241	It is recommended that a LLD set 'resid' on data transfers from a SCSI
	1242	target device (e.g. READs). It is especially important that 'resid' is set
	1243	when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
	1244	(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
	1245	data has been received then the safest approach is to indicate no bytes have
	1246	been received. For example: to indicate that no valid data has been received
	1247	a LLD might use these helpers::
	1248
	1249	scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
	1250
	1251	where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
	1252	bytes blocks has been received 'resid' could be set like this::
	1253
	1254	scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
	1255
	1256	The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
	1257
	1258
	1259	Locks
	1260	=====
	1261	Each struct Scsi_Host instance has a spin_lock called struct
	1262	Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
	1263	hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
	1264	is initialized to point at default_lock. Thereafter lock and unlock
	1265	operations performed by the mid level use the struct Scsi_Host::host_lock
	1266	pointer. Previously drivers could override the host_lock pointer but
	1267	this is not allowed anymore.
	1268
	1269
	1270	Autosense
	1271	=========
	1272	Autosense (or auto-sense) is defined in the SAM-2 document as "the
	1273	automatic return of sense data to the application client coincident
	1274	with the completion of a SCSI command" when a status of CHECK CONDITION
	1275	occurs. LLDs should perform autosense. This should be done when the LLD
	1276	detects a CHECK CONDITION status by either:
	1277
	1278	a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
	1279	to perform an extra data in phase on such responses
	1280	b) or, the LLD issuing a REQUEST SENSE command itself
	1281
	1282	Either way, when a status of CHECK CONDITION is detected, the mid level
	1283	decides whether the LLD has performed autosense by checking struct
	1284	scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
	1285	then autosense is assumed to have taken place. If it has another value (and
	1286	this byte is initialized to 0 before each command) then the mid level will
	1287	issue a REQUEST SENSE command.
	1288
	1289	In the presence of queued commands the "nexus" that maintains sense
	1290	buffer data from the command that failed until a following REQUEST SENSE
	1291	may get out of synchronization. This is why it is best for the LLD
	1292	to perform autosense.
	1293
	1294
	1295	Changes since lk 2.4 series
	1296	===========================
	1297	io_request_lock has been replaced by several finer grained locks. The lock
	1298	relevant to LLDs is struct Scsi_Host::host_lock and there is
	1299	one per SCSI host.
	1300
	1301	The older error handling mechanism has been removed. This means the
	1302	LLD interface functions abort() and reset() have been removed.
	1303	The struct scsi_host_template::use_new_eh_code flag has been removed.
	1304
	1305	In the 2.4 series the SCSI subsystem configuration descriptions were
	1306	aggregated with the configuration descriptions from all other Linux
	1307	subsystems in the Documentation/Configure.help file. In the 2.6 series,
	1308	the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
	1309	file that contains both configuration and help information.
	1310
	1311	struct SHT has been renamed to struct scsi_host_template.
	1312
	1313	Addition of the "hotplug initialization model" and many extra functions
	1314	to support it.
	1315
	1316
	1317	Credits
	1318	=======
	1319	The following people have contributed to this document:
	1320
	1321	- Mike Anderson <andmike at us dot ibm dot com>
	1322	- James Bottomley <James dot Bottomley at hansenpartnership dot com>
	1323	- Patrick Mansfield <patmans at us dot ibm dot com>
	1324	- Christoph Hellwig <hch at infradead dot org>
	1325	- Doug Ledford <dledford at redhat dot com>
	1326	- Andries Brouwer <Andries dot Brouwer at cwi dot nl>
	1327	- Randy Dunlap <rdunlap at xenotime dot net>
	1328	- Alan Stern <stern at rowland dot harvard dot edu>
	1329
	1330
	1331	Douglas Gilbert
	1332	dgilbert at interlog dot com
	1333
	1334	21st September 2004

Documentation/scsi/scsi_mid_low_api.txt+0−1280

@@ -1,1280 +0,0 @@
1	Linux Kernel 2.6 series
2	SCSI mid_level - lower_level driver interface
3	=============================================
4
5	Introduction
6	============
7	This document outlines the interface between the Linux SCSI mid level and
8	SCSI lower level drivers. Lower level drivers (LLDs) are variously called
9	host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
10	context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
11	single SCSI initiator port on a SCSI transport. An "initiator" port
12	(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
13	to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
14	system, but only one per hardware type. Most LLDs can control one or more
15	SCSI HBAs. Some HBAs contain multiple hosts.
16
17	In some cases the SCSI transport is an external bus that already has
18	its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
19	SCSI subsystem LLD is a software bridge to the other driver subsystem.
20	Examples are the usb-storage driver (found in the drivers/usb/storage
21	directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
22	directory).
23
24	For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
25	(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
26	LLD can be built into the kernel or loaded as a module. There can only be
27	one aic7xxx LLD running in a Linux system but it may be controlling many
28	HBAs. These HBAs might be either on PCI daughter-boards or built into
29	the motherboard (or both). Some aic7xxx based HBAs are dual controllers
30	and thus represent two hosts. Like most modern HBAs, each aic7xxx host
31	has its own PCI device address. [The one-to-one correspondence between
32	a SCSI host and a PCI device is common but not required (e.g. with
33	ISA adapters).]
34
35	The SCSI mid level isolates an LLD from other layers such as the SCSI
36	upper layer drivers and the block layer.
37
38	This version of the document roughly matches linux kernel version 2.6.8 .
39
40	Documentation
41	=============
42	There is a SCSI documentation directory within the kernel source tree,
43	typically Documentation/scsi . Most documents are in plain
44	(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
45	found in that directory. A more recent copy of this document may be found
46	at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
47	Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
48	briefly described in scsi.txt which contains a url to a document
49	describing the SCSI subsystem in the lk 2.4 series. Two upper level
50	drivers have documents in that directory: st.txt (SCSI tape driver) and
51	scsi-generic.txt (for the sg driver).
52
53	Some documentation (or urls) for LLDs may be found in the C source code
54	or in the same directory as the C source code. For example to find a url
55	about the USB mass storage driver see the
56	/usr/src/linux/drivers/usb/storage directory.
57
58	Driver structure
59	================
60	Traditionally an LLD for the SCSI subsystem has been at least two files in
61	the drivers/scsi directory. For example, a driver called "xyz" has a header
62	file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
63	why this couldn't all be in one file; the header file is superfluous.] Some
64	drivers that have been ported to several operating systems have more than
65	two files. For example the aic7xxx driver has separate files for generic
66	and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
67	their own directory under the drivers/scsi directory.
68
69	When a new LLD is being added to Linux, the following files (found in the
70	drivers/scsi directory) will need some attention: Makefile and Kconfig .
71	It is probably best to study how existing LLDs are organized.
72
73	As the 2.5 series development kernels evolve into the 2.6 series
74	production series, changes are being introduced into this interface. An
75	example of this is driver initialization code where there are now 2 models
76	available. The older one, similar to what was found in the lk 2.4 series,
77	is based on hosts that are detected at HBA driver load time. This will be
78	referred to the "passive" initialization model. The newer model allows HBAs
79	to be hot plugged (and unplugged) during the lifetime of the LLD and will
80	be referred to as the "hotplug" initialization model. The newer model is
81	preferred as it can handle both traditional SCSI equipment that is
82	permanently connected as well as modern "SCSI" devices (e.g. USB or
83	IEEE 1394 connected digital cameras) that are hotplugged. Both
84	initialization models are discussed in the following sections.
85
86	An LLD interfaces to the SCSI subsystem several ways:
87	a) directly invoking functions supplied by the mid level
88	b) passing a set of function pointers to a registration function
89	supplied by the mid level. The mid level will then invoke these
90	functions at some point in the future. The LLD will supply
91	implementations of these functions.
92	c) direct access to instances of well known data structures maintained
93	by the mid level
94
95	Those functions in group a) are listed in a section entitled "Mid level
96	supplied functions" below.
97
98	Those functions in group b) are listed in a section entitled "Interface
99	functions" below. Their function pointers are placed in the members of
100	"struct scsi_host_template", an instance of which is passed to
101	scsi_host_alloc() ** . Those interface functions that the LLD does not
102	wish to supply should have NULL placed in the corresponding member of
103	struct scsi_host_template. Defining an instance of struct
104	scsi_host_template at file scope will cause NULL to be placed in function
105	pointer members not explicitly initialized.
106
107	Those usages in group c) should be handled with care, especially in a
108	"hotplug" environment. LLDs should be aware of the lifetime of instances
109	that are shared with the mid level and other layers.
110
111	All functions defined within an LLD and all data defined at file scope
112	should be static. For example the slave_alloc() function in an LLD
113	called "xxx" could be defined as
114	"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
115
116	** the scsi_host_alloc() function is a replacement for the rather vaguely
117	named scsi_register() function in most situations.
118
119
120	Hotplug initialization model
121	============================
122	In this model an LLD controls when SCSI hosts are introduced and removed
123	from the SCSI subsystem. Hosts can be introduced as early as driver
124	initialization and removed as late as driver shutdown. Typically a driver
125	will respond to a sysfs probe() callback that indicates an HBA has been
126	detected. After confirming that the new device is one that the LLD wants
127	to control, the LLD will initialize the HBA and then register a new host
128	with the SCSI mid level.
129
130	During LLD initialization the driver should register itself with the
131	appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
132	This can probably be done via sysfs. Any driver parameters (especially
133	those that are writable after the driver is loaded) could also be
134	registered with sysfs at this point. The SCSI mid level first becomes
135	aware of an LLD when that LLD registers its first HBA.
136
137	At some later time, the LLD becomes aware of an HBA and what follows
138	is a typical sequence of calls between the LLD and the mid level.
139	This example shows the mid level scanning the newly introduced HBA for 3
140	scsi devices of which only the first 2 respond:
141
142	HBA PROBE: assume 2 SCSI devices found in scan
143	LLD mid level LLD
144	===-------------------=========--------------------===------
145	scsi_host_alloc() -->
146	scsi_add_host() ---->
147	scsi_scan_host() -------+
148	\|
149	slave_alloc()
150	slave_configure() --> scsi_change_queue_depth()
151	\|
152	slave_alloc()
153	slave_configure()
154	\|
155	slave_alloc() ***
156	slave_destroy() ***
157	------------------------------------------------------------
158
159	If the LLD wants to adjust the default queue settings, it can invoke
160	scsi_change_queue_depth() in its slave_configure() routine.
161
162	*** For scsi devices that the mid level tries to scan but do not
163	respond, a slave_alloc(), slave_destroy() pair is called.
164
165	When an HBA is being removed it could be as part of an orderly shutdown
166	associated with the LLD module being unloaded (e.g. with the "rmmod"
167	command) or in response to a "hot unplug" indicated by sysfs()'s
168	remove() callback being invoked. In either case, the sequence is the
169	same:
170
171	HBA REMOVE: assume 2 SCSI devices attached
172	LLD mid level LLD
173	===----------------------=========-----------------===------
174	scsi_remove_host() ---------+
175	\|
176	slave_destroy()
177	slave_destroy()
178	scsi_host_put()
179	------------------------------------------------------------
180
181	It may be useful for a LLD to keep track of struct Scsi_Host instances
182	(a pointer is returned by scsi_host_alloc()). Such instances are "owned"
183	by the mid-level. struct Scsi_Host instances are freed from
184	scsi_host_put() when the reference count hits zero.
185
186	Hot unplugging an HBA that controls a disk which is processing SCSI
187	commands on a mounted file system is an interesting situation. Reference
188	counting logic is being introduced into the mid level to cope with many
189	of the issues involved. See the section on reference counting below.
190
191
192	The hotplug concept may be extended to SCSI devices. Currently, when an
193	HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
194	attached to the HBA's SCSI transport. On newer SCSI transports the HBA
195	may become aware of a new SCSI device _after_ the scan has completed.
196	An LLD can use this sequence to make the mid level aware of a SCSI device:
197
198	SCSI DEVICE hotplug
199	LLD mid level LLD
200	===-------------------=========--------------------===------
201	scsi_add_device() ------+
202	\|
203	slave_alloc()
204	slave_configure() [--> scsi_change_queue_depth()]
205	------------------------------------------------------------
206
207	In a similar fashion, an LLD may become aware that a SCSI device has been
208	removed (unplugged) or the connection to it has been interrupted. Some
209	existing SCSI transports (e.g. SPI) may not become aware that a SCSI
210	device has been removed until a subsequent SCSI command fails which will
211	probably cause that device to be set offline by the mid level. An LLD that
212	detects the removal of a SCSI device can instigate its removal from
213	upper layers with this sequence:
214
215	SCSI DEVICE hot unplug
216	LLD mid level LLD
217	===----------------------=========-----------------===------
218	scsi_remove_device() -------+
219	\|
220	slave_destroy()
221	------------------------------------------------------------
222
223	It may be useful for an LLD to keep track of struct scsi_device instances
224	(a pointer is passed as the parameter to slave_alloc() and
225	slave_configure() callbacks). Such instances are "owned" by the mid-level.
226	struct scsi_device instances are freed after slave_destroy().
227
228
229	Reference Counting
230	==================
231	The Scsi_Host structure has had reference counting infrastructure added.
232	This effectively spreads the ownership of struct Scsi_Host instances
233	across the various SCSI layers which use them. Previously such instances
234	were exclusively owned by the mid level. LLDs would not usually need to
235	directly manipulate these reference counts but there may be some cases
236	where they do.
237
238	There are 3 reference counting functions of interest associated with
239	struct Scsi_Host:
240	- scsi_host_alloc(): returns a pointer to new instance of struct
241	Scsi_Host which has its reference count ^^ set to 1
242	- scsi_host_get(): adds 1 to the reference count of the given instance
243	- scsi_host_put(): decrements 1 from the reference count of the given
244	instance. If the reference count reaches 0 then the given instance
245	is freed
246
247	The scsi_device structure has had reference counting infrastructure added.
248	This effectively spreads the ownership of struct scsi_device instances
249	across the various SCSI layers which use them. Previously such instances
250	were exclusively owned by the mid level. See the access functions declared
251	towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
252	a copy of a pointer to a scsi_device instance it should use scsi_device_get()
253	to bump its reference count. When it is finished with the pointer it can
254	use scsi_device_put() to decrement its reference count (and potentially
255	delete it).
256
257	^^ struct Scsi_Host actually has 2 reference counts which are manipulated
258	in parallel by these functions.
259
260
261	Conventions
262	===========
263	First, Linus Torvalds's thoughts on C coding style can be found in the
264	Documentation/process/coding-style.rst file.
265
266	Next, there is a movement to "outlaw" typedefs introducing synonyms for
267	struct tags. Both can be still found in the SCSI subsystem, but
268	the typedefs have been moved to a single file, scsi_typedefs.h to
269	make their future removal easier, for example:
270	"typedef struct scsi_cmnd Scsi_Cmnd;"
271
272	Also, most C99 enhancements are encouraged to the extent they are supported
273	by the relevant gcc compilers. So C99 style structure and array
274	initializers are encouraged where appropriate. Don't go too far,
275	VLAs are not properly supported yet. An exception to this is the use of
276	"//" style comments; /.../ comments are still preferred in Linux.
277
278	Well written, tested and documented code, need not be re-formatted to
279	comply with the above conventions. For example, the aic7xxx driver
280	comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
281	and Adaptec have their own coding conventions.
282
283
284	Mid level supplied functions
285	============================
286	These functions are supplied by the SCSI mid level for use by LLDs.
287	The names (i.e. entry points) of these functions are exported
288	so an LLD that is a module can access them. The kernel will
289	arrange for the SCSI mid level to be loaded and initialized before any LLD
290	is initialized. The functions below are listed alphabetically and their
291	names all start with "scsi_".
292
293	Summary:
294	scsi_add_device - creates new scsi device (lu) instance
295	scsi_add_host - perform sysfs registration and set up transport class
296	scsi_change_queue_depth - change the queue depth on a SCSI device
297	scsi_bios_ptable - return copy of block device's partition table
298	scsi_block_requests - prevent further commands being queued to given host
299	scsi_host_alloc - return a new scsi_host instance whose refcount==1
300	scsi_host_get - increments Scsi_Host instance's refcount
301	scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
302	scsi_partsize - parse partition table into cylinders, heads + sectors
303	scsi_register - create and register a scsi host adapter instance.
304	scsi_remove_device - detach and remove a SCSI device
305	scsi_remove_host - detach and remove all SCSI devices owned by host
306	scsi_report_bus_reset - report scsi _bus_ reset observed
307	scsi_scan_host - scan SCSI bus
308	scsi_track_queue_full - track successive QUEUE_FULL events
309	scsi_unblock_requests - allow further commands to be queued to given host
310	scsi_unregister - [calls scsi_host_put()]
311
312
313	Details:
314
315	/**
316	* scsi_add_device - creates new scsi device (lu) instance
317	* @shost: pointer to scsi host instance
318	* @channel: channel number (rarely other than 0)
319	* @id: target id number
320	* @lun: logical unit number
321	*
322	* Returns pointer to new struct scsi_device instance or
323	* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
324	* wrong (e.g. no lu responds at given address)
325	*
326	* Might block: yes
327	*
328	* Notes: This call is usually performed internally during a scsi
329	* bus scan when an HBA is added (i.e. scsi_scan_host()). So it
330	* should only be called if the HBA becomes aware of a new scsi
331	* device (lu) after scsi_scan_host() has completed. If successful
332	* this call can lead to slave_alloc() and slave_configure() callbacks
333	* into the LLD.
334	*
335	* Defined in: drivers/scsi/scsi_scan.c
336	**/
337	struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
338	unsigned int channel,
339	unsigned int id, unsigned int lun)
340
341
342	/**
343	* scsi_add_host - perform sysfs registration and set up transport class
344	* @shost: pointer to scsi host instance
345	* @dev: pointer to struct device of type scsi class
346	*
347	* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
348	*
349	* Might block: no
350	*
351	* Notes: Only required in "hotplug initialization model" after a
352	* successful call to scsi_host_alloc(). This function does not
353	* scan the bus; this can be done by calling scsi_scan_host() or
354	* in some other transport-specific way. The LLD must set up
355	* the transport template before calling this function and may only
356	* access the transport class data after this function has been called.
357	*
358	* Defined in: drivers/scsi/hosts.c
359	**/
360	int scsi_add_host(struct Scsi_Host shost, struct device dev)
361
362
363	/**
364	* scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
365	* @sdev: pointer to SCSI device to change queue depth on
366	* @tags Number of tags allowed if tagged queuing enabled,
367	* or number of commands the LLD can queue up
368	* in non-tagged mode (as per cmd_per_lun).
369	*
370	* Returns nothing
371	*
372	* Might block: no
373	*
374	* Notes: Can be invoked any time on a SCSI device controlled by this
375	* LLD. [Specifically during and after slave_configure() and prior to
376	* slave_destroy().] Can safely be invoked from interrupt code.
377	*
378	* Defined in: drivers/scsi/scsi.c [see source code for more notes]
379	*
380	**/
381	int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
382
383
384	/**
385	* scsi_bios_ptable - return copy of block device's partition table
386	* @dev: pointer to block device
387	*
388	* Returns pointer to partition table, or NULL for failure
389	*
390	* Might block: yes
391	*
392	* Notes: Caller owns memory returned (free with kfree() )
393	*
394	* Defined in: drivers/scsi/scsicam.c
395	**/
396	unsigned char scsi_bios_ptable(struct block_device dev)
397
398
399	/**
400	* scsi_block_requests - prevent further commands being queued to given host
401	*
402	* @shost: pointer to host to block commands on
403	*
404	* Returns nothing
405	*
406	* Might block: no
407	*
408	* Notes: There is no timer nor any other means by which the requests
409	* get unblocked other than the LLD calling scsi_unblock_requests().
410	*
411	* Defined in: drivers/scsi/scsi_lib.c
412	**/
413	void scsi_block_requests(struct Scsi_Host * shost)
414
415
416	/**
417	* scsi_host_alloc - create a scsi host adapter instance and perform basic
418	* initialization.
419	* @sht: pointer to scsi host template
420	* @privsize: extra bytes to allocate in hostdata array (which is the
421	* last member of the returned Scsi_Host instance)
422	*
423	* Returns pointer to new Scsi_Host instance or NULL on failure
424	*
425	* Might block: yes
426	*
427	* Notes: When this call returns to the LLD, the SCSI bus scan on
428	* this host has _not_ yet been done.
429	* The hostdata array (by default zero length) is a per host scratch
430	* area for the LLD's exclusive use.
431	* Both associated refcounting objects have their refcount set to 1.
432	* Full registration (in sysfs) and a bus scan are performed later when
433	* scsi_add_host() and scsi_scan_host() are called.
434	*
435	* Defined in: drivers/scsi/hosts.c .
436	**/
437	struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
438	int privsize)
439
440
441	/**
442	* scsi_host_get - increment Scsi_Host instance refcount
443	* @shost: pointer to struct Scsi_Host instance
444	*
445	* Returns nothing
446	*
447	* Might block: currently may block but may be changed to not block
448	*
449	* Notes: Actually increments the counts in two sub-objects
450	*
451	* Defined in: drivers/scsi/hosts.c
452	**/
453	void scsi_host_get(struct Scsi_Host *shost)
454
455
456	/**
457	* scsi_host_put - decrement Scsi_Host instance refcount, free if 0
458	* @shost: pointer to struct Scsi_Host instance
459	*
460	* Returns nothing
461	*
462	* Might block: currently may block but may be changed to not block
463	*
464	* Notes: Actually decrements the counts in two sub-objects. If the
465	* latter refcount reaches 0, the Scsi_Host instance is freed.
466	* The LLD need not worry exactly when the Scsi_Host instance is
467	* freed, it just shouldn't access the instance after it has balanced
468	* out its refcount usage.
469	*
470	* Defined in: drivers/scsi/hosts.c
471	**/
472	void scsi_host_put(struct Scsi_Host *shost)
473
474
475	/**
476	* scsi_partsize - parse partition table into cylinders, heads + sectors
477	* @buf: pointer to partition table
478	* @capacity: size of (total) disk in 512 byte sectors
479	* @cyls: outputs number of cylinders calculated via this pointer
480	* @hds: outputs number of heads calculated via this pointer
481	* @secs: outputs number of sectors calculated via this pointer
482	*
483	* Returns 0 on success, -1 on failure
484	*
485	* Might block: no
486	*
487	* Notes: Caller owns memory returned (free with kfree() )
488	*
489	* Defined in: drivers/scsi/scsicam.c
490	**/
491	int scsi_partsize(unsigned char *buf, unsigned long capacity,
492	unsigned int cyls, unsigned int hds, unsigned int *secs)
493
494
495	/**
496	* scsi_register - create and register a scsi host adapter instance.
497	* @sht: pointer to scsi host template
498	* @privsize: extra bytes to allocate in hostdata array (which is the
499	* last member of the returned Scsi_Host instance)
500	*
501	* Returns pointer to new Scsi_Host instance or NULL on failure
502	*
503	* Might block: yes
504	*
505	* Notes: When this call returns to the LLD, the SCSI bus scan on
506	* this host has _not_ yet been done.
507	* The hostdata array (by default zero length) is a per host scratch
508	* area for the LLD.
509	*
510	* Defined in: drivers/scsi/hosts.c .
511	**/
512	struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
513	int privsize)
514
515
516	/**
517	* scsi_remove_device - detach and remove a SCSI device
518	* @sdev: a pointer to a scsi device instance
519	*
520	* Returns value: 0 on success, -EINVAL if device not attached
521	*
522	* Might block: yes
523	*
524	* Notes: If an LLD becomes aware that a scsi device (lu) has
525	* been removed but its host is still present then it can request
526	* the removal of that scsi device. If successful this call will
527	* lead to the slave_destroy() callback being invoked. sdev is an
528	* invalid pointer after this call.
529	*
530	* Defined in: drivers/scsi/scsi_sysfs.c .
531	**/
532	int scsi_remove_device(struct scsi_device *sdev)
533
534
535	/**
536	* scsi_remove_host - detach and remove all SCSI devices owned by host
537	* @shost: a pointer to a scsi host instance
538	*
539	* Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)
540	*
541	* Might block: yes
542	*
543	* Notes: Should only be invoked if the "hotplug initialization
544	* model" is being used. It should be called _prior_ to
545	* scsi_unregister().
546	*
547	* Defined in: drivers/scsi/hosts.c .
548	**/
549	int scsi_remove_host(struct Scsi_Host *shost)
550
551
552	/**
553	* scsi_report_bus_reset - report scsi _bus_ reset observed
554	* @shost: a pointer to a scsi host involved
555	* @channel: channel (within) host on which scsi bus reset occurred
556	*
557	* Returns nothing
558	*
559	* Might block: no
560	*
561	* Notes: This only needs to be called if the reset is one which
562	* originates from an unknown location. Resets originated by the
563	* mid level itself don't need to call this, but there should be
564	* no harm. The main purpose of this is to make sure that a
565	* CHECK_CONDITION is properly treated.
566	*
567	* Defined in: drivers/scsi/scsi_error.c .
568	**/
569	void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)
570
571
572	/**
573	* scsi_scan_host - scan SCSI bus
574	* @shost: a pointer to a scsi host instance
575	*
576	* Might block: yes
577	*
578	* Notes: Should be called after scsi_add_host()
579	*
580	* Defined in: drivers/scsi/scsi_scan.c
581	**/
582	void scsi_scan_host(struct Scsi_Host *shost)
583
584
585	/**
586	* scsi_track_queue_full - track successive QUEUE_FULL events on given
587	* device to determine if and when there is a need
588	* to adjust the queue depth on the device.
589	* @sdev: pointer to SCSI device instance
590	* @depth: Current number of outstanding SCSI commands on this device,
591	* not counting the one returned as QUEUE_FULL.
592	*
593	* Returns 0 - no change needed
594	* >0 - adjust queue depth to this new depth
595	* -1 - drop back to untagged operation using host->cmd_per_lun
596	* as the untagged command depth
597	*
598	* Might block: no
599	*
600	* Notes: LLDs may call this at any time and we will do "The Right
601	* Thing"; interrupt context safe.
602	*
603	* Defined in: drivers/scsi/scsi.c .
604	**/
605	int scsi_track_queue_full(struct scsi_device *sdev, int depth)
606
607
608	/**
609	* scsi_unblock_requests - allow further commands to be queued to given host
610	*
611	* @shost: pointer to host to unblock commands on
612	*
613	* Returns nothing
614	*
615	* Might block: no
616	*
617	* Defined in: drivers/scsi/scsi_lib.c .
618	**/
619	void scsi_unblock_requests(struct Scsi_Host * shost)
620
621
622	/**
623	* scsi_unregister - unregister and free memory used by host instance
624	* @shp: pointer to scsi host instance to unregister.
625	*
626	* Returns nothing
627	*
628	* Might block: no
629	*
630	* Notes: Should not be invoked if the "hotplug initialization
631	* model" is being used. Called internally by exit_this_scsi_driver()
632	* in the "passive initialization model". Hence a LLD has no need to
633	* call this function directly.
634	*
635	* Defined in: drivers/scsi/hosts.c .
636	**/
637	void scsi_unregister(struct Scsi_Host * shp)
638
639
640
641
642	Interface Functions
643	===================
644	Interface functions are supplied (defined) by LLDs and their function
645	pointers are placed in an instance of struct scsi_host_template which
646	is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].
647	Some are mandatory. Interface functions should be declared static. The
648	accepted convention is that driver "xyz" will declare its slave_configure()
649	function as:
650	static int xyz_slave_configure(struct scsi_device * sdev);
651	and so forth for all interface functions listed below.
652
653	A pointer to this function should be placed in the 'slave_configure' member
654	of a "struct scsi_host_template" instance. A pointer to such an instance
655	should be passed to the mid level's scsi_host_alloc() [or scsi_register() /
656	init_this_scsi_driver()].
657
658	The interface functions are also described in the include/scsi/scsi_host.h
659	file immediately above their definition point in "struct scsi_host_template".
660	In some cases more detail is given in scsi_host.h than below.
661
662	The interface functions are listed below in alphabetical order.
663
664	Summary:
665	bios_param - fetch head, sector, cylinder info for a disk
666	eh_timed_out - notify the host that a command timer expired
667	eh_abort_handler - abort given command
668	eh_bus_reset_handler - issue SCSI bus reset
669	eh_device_reset_handler - issue SCSI device reset
670	eh_host_reset_handler - reset host (host bus adapter)
671	info - supply information about given host
672	ioctl - driver can respond to ioctls
673	proc_info - supports /proc/scsi/{driver_name}/{host_no}
674	queuecommand - queue scsi command, invoke 'done' on completion
675	slave_alloc - prior to any commands being sent to a new device
676	slave_configure - driver fine tuning for given device after attach
677	slave_destroy - given device is about to be shut down
678
679
680	Details:
681
682	/**
683	* bios_param - fetch head, sector, cylinder info for a disk
684	* @sdev: pointer to scsi device context (defined in
685	* include/scsi/scsi_device.h)
686	* @bdev: pointer to block device context (defined in fs.h)
687	* @capacity: device size (in 512 byte sectors)
688	* @params: three element array to place output:
689	* params[0] number of heads (max 255)
690	* params[1] number of sectors (max 63)
691	* params[2] number of cylinders
692	*
693	* Return value is ignored
694	*
695	* Locks: none
696	*
697	* Calling context: process (sd)
698	*
699	* Notes: an arbitrary geometry (based on READ CAPACITY) is used
700	* if this function is not provided. The params array is
701	* pre-initialized with made up values just in case this function
702	* doesn't output anything.
703	*
704	* Optionally defined in: LLD
705	**/
706	int bios_param(struct scsi_device * sdev, struct block_device *bdev,
707	sector_t capacity, int params[3])
708
709
710	/**
711	* eh_timed_out - The timer for the command has just fired
712	* @scp: identifies command timing out
713	*
714	* Returns:
715	*
716	* EH_HANDLED: I fixed the error, please complete the command
717	* EH_RESET_TIMER: I need more time, reset the timer and
718	* begin counting again
719	* EH_NOT_HANDLED Begin normal error recovery
720	*
721	*
722	* Locks: None held
723	*
724	* Calling context: interrupt
725	*
726	* Notes: This is to give the LLD an opportunity to do local recovery.
727	* This recovery is limited to determining if the outstanding command
728	* will ever complete. You may not abort and restart the command from
729	* this callback.
730	*
731	* Optionally defined in: LLD
732	**/
733	int eh_timed_out(struct scsi_cmnd * scp)
734
735
736	/**
737	* eh_abort_handler - abort command associated with scp
738	* @scp: identifies command to be aborted
739	*
740	* Returns SUCCESS if command aborted else FAILED
741	*
742	* Locks: None held
743	*
744	* Calling context: kernel thread
745	*
746	* Notes: If 'no_async_abort' is defined this callback
747	* will be invoked from scsi_eh thread. No other commands
748	* will then be queued on current host during eh.
749	* Otherwise it will be called whenever scsi_times_out()
750	* is called due to a command timeout.
751	*
752	* Optionally defined in: LLD
753	**/
754	int eh_abort_handler(struct scsi_cmnd * scp)
755
756
757	/**
758	* eh_bus_reset_handler - issue SCSI bus reset
759	* @scp: SCSI bus that contains this device should be reset
760	*
761	* Returns SUCCESS if command aborted else FAILED
762	*
763	* Locks: None held
764	*
765	* Calling context: kernel thread
766	*
767	* Notes: Invoked from scsi_eh thread. No other commands will be
768	* queued on current host during eh.
769	*
770	* Optionally defined in: LLD
771	**/
772	int eh_bus_reset_handler(struct scsi_cmnd * scp)
773
774
775	/**
776	* eh_device_reset_handler - issue SCSI device reset
777	* @scp: identifies SCSI device to be reset
778	*
779	* Returns SUCCESS if command aborted else FAILED
780	*
781	* Locks: None held
782	*
783	* Calling context: kernel thread
784	*
785	* Notes: Invoked from scsi_eh thread. No other commands will be
786	* queued on current host during eh.
787	*
788	* Optionally defined in: LLD
789	**/
790	int eh_device_reset_handler(struct scsi_cmnd * scp)
791
792
793	/**
794	* eh_host_reset_handler - reset host (host bus adapter)
795	* @scp: SCSI host that contains this device should be reset
796	*
797	* Returns SUCCESS if command aborted else FAILED
798	*
799	* Locks: None held
800	*
801	* Calling context: kernel thread
802	*
803	* Notes: Invoked from scsi_eh thread. No other commands will be
804	* queued on current host during eh.
805	* With the default eh_strategy in place, if none of the _abort_,
806	* _device_reset_, _bus_reset_ or this eh handler function are
807	* defined (or they all return FAILED) then the device in question
808	* will be set offline whenever eh is invoked.
809	*
810	* Optionally defined in: LLD
811	**/
812	int eh_host_reset_handler(struct scsi_cmnd * scp)
813
814
815	/**
816	* info - supply information about given host: driver name plus data
817	* to distinguish given host
818	* @shp: host to supply information about
819	*
820	* Return ASCII null terminated string. [This driver is assumed to
821	* manage the memory pointed to and maintain it, typically for the
822	* lifetime of this host.]
823	*
824	* Locks: none
825	*
826	* Calling context: process
827	*
828	* Notes: Often supplies PCI or ISA information such as IO addresses
829	* and interrupt numbers. If not supplied struct Scsi_Host::name used
830	* instead. It is assumed the returned information fits on one line
831	* (i.e. does not included embedded newlines).
832	* The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
833	* function (or struct Scsi_Host::name if this function is not
834	* available).
835	* In a similar manner, init_this_scsi_driver() outputs to the console
836	* each host's "info" (or name) for the driver it is registering.
837	* Also if proc_info() is not supplied, the output of this function
838	* is used instead.
839	*
840	* Optionally defined in: LLD
841	**/
842	const char * info(struct Scsi_Host * shp)
843
844
845	/**
846	* ioctl - driver can respond to ioctls
847	* @sdp: device that ioctl was issued for
848	* @cmd: ioctl number
849	* @arg: pointer to read or write data from. Since it points to
850	* user space, should use appropriate kernel functions
851	* (e.g. copy_from_user() ). In the Unix style this argument
852	* can also be viewed as an unsigned long.
853	*
854	* Returns negative "errno" value when there is a problem. 0 or a
855	* positive value indicates success and is returned to the user space.
856	*
857	* Locks: none
858	*
859	* Calling context: process
860	*
861	* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
862	* The user issues an ioctl() against an upper level driver
863	* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
864	* the 'cmd' then it is passed to the SCSI mid level. If the SCSI
865	* mid level does not recognize it, then the LLD that controls
866	* the device receives the ioctl. According to recent Unix standards
867	* unsupported ioctl() 'cmd' numbers should return -ENOTTY.
868	*
869	* Optionally defined in: LLD
870	**/
871	int ioctl(struct scsi_device sdp, int cmd, void arg)
872
873
874	/**
875	* proc_info - supports /proc/scsi/{driver_name}/{host_no}
876	* @buffer: anchor point to output to (0==writeto1_read0) or fetch from
877	* (1==writeto1_read0).
878	* @start: where "interesting" data is written to. Ignored when
879	* 1==writeto1_read0.
880	* @offset: offset within buffer 0==writeto1_read0 is actually
881	* interested in. Ignored when 1==writeto1_read0 .
882	* @length: maximum (or actual) extent of buffer
883	* @host_no: host number of interest (struct Scsi_Host::host_no)
884	* @writeto1_read0: 1 -> data coming from user space towards driver
885	* (e.g. "echo some_string > /proc/scsi/xyz/2")
886	* 0 -> user what data from this driver
887	* (e.g. "cat /proc/scsi/xyz/2")
888	*
889	* Returns length when 1==writeto1_read0. Otherwise number of chars
890	* output to buffer past offset.
891	*
892	* Locks: none held
893	*
894	* Calling context: process
895	*
896	* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
897	* support can now be configured out of the scsi subsystem.
898	*
899	* Optionally defined in: LLD
900	**/
901	int proc_info(char * buffer, char ** start, off_t offset,
902	int length, int host_no, int writeto1_read0)
903
904
905	/**
906	* queuecommand - queue scsi command, invoke scp->scsi_done on completion
907	* @shost: pointer to the scsi host object
908	* @scp: pointer to scsi command object
909	*
910	* Returns 0 on success.
911	*
912	* If there's a failure, return either:
913	*
914	* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
915	* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
916	*
917	* On both of these returns, the mid-layer will requeue the I/O
918	*
919	* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
920	* device will be paused, and it will be unpaused when a command to
921	* the device returns (or after a brief delay if there are no more
922	* outstanding commands to it). Commands to other devices continue
923	* to be processed normally.
924	*
925	* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
926	* is paused and will be unpaused when any command returns from
927	* the host (or after a brief delay if there are no outstanding
928	* commands to the host).
929	*
930	* For compatibility with earlier versions of queuecommand, any
931	* other return value is treated the same as
932	* SCSI_MLQUEUE_HOST_BUSY.
933	*
934	* Other types of errors that are detected immediately may be
935	* flagged by setting scp->result to an appropriate value,
936	* invoking the scp->scsi_done callback, and then returning 0
937	* from this function. If the command is not performed
938	* immediately (and the LLD is starting (or will start) the given
939	* command) then this function should place 0 in scp->result and
940	* return 0.
941	*
942	* Command ownership. If the driver returns zero, it owns the
943	* command and must take responsibility for ensuring the
944	* scp->scsi_done callback is executed. Note: the driver may
945	* call scp->scsi_done before returning zero, but after it has
946	* called scp->scsi_done, it may not return any value other than
947	* zero. If the driver makes a non-zero return, it must not
948	* execute the command's scsi_done callback at any time.
949	*
950	* Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
951	* held on entry (with "irqsave") and is expected to be
952	* held on return. From 2.6.37 onwards, queuecommand is
953	* called without any locks held.
954	*
955	* Calling context: in interrupt (soft irq) or process context
956	*
957	* Notes: This function should be relatively fast. Normally it
958	* will not wait for IO to complete. Hence the scp->scsi_done
959	* callback is invoked (often directly from an interrupt service
960	* routine) some time after this function has returned. In some
961	* cases (e.g. pseudo adapter drivers that manufacture the
962	* response to a SCSI INQUIRY) the scp->scsi_done callback may be
963	* invoked before this function returns. If the scp->scsi_done
964	* callback is not invoked within a certain period the SCSI mid
965	* level will commence error processing. If a status of CHECK
966	* CONDITION is placed in "result" when the scp->scsi_done
967	* callback is invoked, then the LLD driver should perform
968	* autosense and fill in the struct scsi_cmnd::sense_buffer
969	* array. The scsi_cmnd::sense_buffer array is zeroed prior to
970	* the mid level queuing a command to an LLD.
971	*
972	* Defined in: LLD
973	**/
974	int queuecommand(struct Scsi_Host shost, struct scsi_cmnd scp)
975
976
977	/**
978	* slave_alloc - prior to any commands being sent to a new device
979	* (i.e. just prior to scan) this call is made
980	* @sdp: pointer to new device (about to be scanned)
981	*
982	* Returns 0 if ok. Any other return is assumed to be an error and
983	* the device is ignored.
984	*
985	* Locks: none
986	*
987	* Calling context: process
988	*
989	* Notes: Allows the driver to allocate any resources for a device
990	* prior to its initial scan. The corresponding scsi device may not
991	* exist but the mid level is just about to scan for it (i.e. send
992	* and INQUIRY command plus ...). If a device is found then
993	* slave_configure() will be called while if a device is not found
994	* slave_destroy() is called.
995	* For more details see the include/scsi/scsi_host.h file.
996	*
997	* Optionally defined in: LLD
998	**/
999	int slave_alloc(struct scsi_device *sdp)
1000
1001
1002	/**
1003	* slave_configure - driver fine tuning for given device just after it
1004	* has been first scanned (i.e. it responded to an
1005	* INQUIRY)
1006	* @sdp: device that has just been attached
1007	*
1008	* Returns 0 if ok. Any other return is assumed to be an error and
1009	* the device is taken offline. [offline devices will _not_ have
1010	* slave_destroy() called on them so clean up resources.]
1011	*
1012	* Locks: none
1013	*
1014	* Calling context: process
1015	*
1016	* Notes: Allows the driver to inspect the response to the initial
1017	* INQUIRY done by the scanning code and take appropriate action.
1018	* For more details see the include/scsi/scsi_host.h file.
1019	*
1020	* Optionally defined in: LLD
1021	**/
1022	int slave_configure(struct scsi_device *sdp)
1023
1024
1025	/**
1026	* slave_destroy - given device is about to be shut down. All
1027	* activity has ceased on this device.
1028	* @sdp: device that is about to be shut down
1029	*
1030	* Returns nothing
1031	*
1032	* Locks: none
1033	*
1034	* Calling context: process
1035	*
1036	* Notes: Mid level structures for given device are still in place
1037	* but are about to be torn down. Any per device resources allocated
1038	* by this driver for given device should be freed now. No further
1039	* commands will be sent for this sdp instance. [However the device
1040	* could be re-attached in the future in which case a new instance
1041	* of struct scsi_device would be supplied by future slave_alloc()
1042	* and slave_configure() calls.]
1043	*
1044	* Optionally defined in: LLD
1045	**/
1046	void slave_destroy(struct scsi_device *sdp)
1047
1048
1049
1050	Data Structures
1051	===============
1052	struct scsi_host_template
1053	-------------------------
1054	There is one "struct scsi_host_template" instance per LLD ***. It is
1055	typically initialized as a file scope static in a driver's header file. That
1056	way members that are not explicitly initialized will be set to 0 or NULL.
1057	Member of interest:
1058	name - name of driver (may contain spaces, please limit to
1059	less than 80 characters)
1060	proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
1061	by sysfs in one of its "drivers" directories. Hence
1062	"proc_name" should only contain characters acceptable
1063	to a Unix file name.
1064	(*queuecommand)() - primary callback that the mid level uses to inject
1065	SCSI commands into an LLD.
1066	The structure is defined and commented in include/scsi/scsi_host.h
1067
1068	*** In extreme situations a single driver may have several instances
1069	if it controls several different classes of hardware (e.g. an LLD
1070	that handles both ISA and PCI cards and has a separate instance of
1071	struct scsi_host_template for each class).
1072
1073	struct Scsi_Host
1074	----------------
1075	There is one struct Scsi_Host instance per host (HBA) that an LLD
1076	controls. The struct Scsi_Host structure has many members in common
1077	with "struct scsi_host_template". When a new struct Scsi_Host instance
1078	is created (in scsi_host_alloc() in hosts.c) those common members are
1079	initialized from the driver's struct scsi_host_template instance. Members
1080	of interest:
1081	host_no - system wide unique number that is used for identifying
1082	this host. Issued in ascending order from 0.
1083	can_queue - must be greater than 0; do not send more than can_queue
1084	commands to the adapter.
1085	this_id - scsi id of host (scsi initiator) or -1 if not known
1086	sg_tablesize - maximum scatter gather elements allowed by host.
1087	Set this to SG_ALL or less to avoid chained SG lists.
1088	Must be at least 1.
1089	max_sectors - maximum number of sectors (usually 512 bytes) allowed
1090	in a single SCSI command. The default value of 0 leads
1091	to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
1092	scsi_host.h) which is currently set to 1024. So for a
1093	disk the maximum transfer size is 512 KB when max_sectors
1094	is not defined. Note that this size may not be sufficient
1095	for disk firmware uploads.
1096	cmd_per_lun - maximum number of commands that can be queued on devices
1097	controlled by the host. Overridden by LLD calls to
1098	scsi_change_queue_depth().
1099	unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
1100	restriction), 0=>can use full 32 bit (or better) DMA
1101	address space
1102	no_async_abort - 1=>Asynchronous aborts are not supported
1103	0=>Timed-out commands will be aborted asynchronously
1104	hostt - pointer to driver's struct scsi_host_template from which
1105	this struct Scsi_Host instance was spawned
1106	hostt->proc_name - name of LLD. This is the driver name that sysfs uses
1107	transportt - pointer to driver's struct scsi_transport_template instance
1108	(if any). FC and SPI transports currently supported.
1109	sh_list - a double linked list of pointers to all struct Scsi_Host
1110	instances (currently ordered by ascending host_no)
1111	my_devices - a double linked list of pointers to struct scsi_device
1112	instances that belong to this host.
1113	hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
1114	is set by the second argument (named 'xtr_bytes') to
1115	scsi_host_alloc() or scsi_register().
1116	vendor_id - a unique value that identifies the vendor supplying
1117	the LLD for the Scsi_Host. Used most often in validating
1118	vendor-specific message requests. Value consists of an
1119	identifier type and a vendor-specific value.
1120	See scsi_netlink.h for a description of valid formats.
1121
1122	The scsi_host structure is defined in include/scsi/scsi_host.h
1123
1124	struct scsi_device
1125	------------------
1126	Generally, there is one instance of this structure for each SCSI logical unit
1127	on a host. Scsi devices connected to a host are uniquely identified by a
1128	channel number, target id and logical unit number (lun).
1129	The structure is defined in include/scsi/scsi_device.h
1130
1131	struct scsi_cmnd
1132	----------------
1133	Instances of this structure convey SCSI commands to the LLD and responses
1134	back to the mid level. The SCSI mid level will ensure that no more SCSI
1135	commands become queued against the LLD than are indicated by
1136	scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
1137	be at least one instance of struct scsi_cmnd available for each SCSI device.
1138	Members of interest:
1139	cmnd - array containing SCSI command
1140	cmnd_len - length (in bytes) of SCSI command
1141	sc_data_direction - direction of data transfer in data phase. See
1142	"enum dma_data_direction" in include/linux/dma-mapping.h
1143	request_bufflen - number of data bytes to transfer (0 if no data phase)
1144	use_sg - ==0 -> no scatter gather list, hence transfer data
1145	to/from request_buffer
1146	- >0 -> scatter gather list (actually an array) in
1147	request_buffer with use_sg elements
1148	request_buffer - either contains data buffer or scatter gather list
1149	depending on the setting of use_sg. Scatter gather
1150	elements are defined by 'struct scatterlist' found
1151	in include/linux/scatterlist.h .
1152	done - function pointer that should be invoked by LLD when the
1153	SCSI command is completed (successfully or otherwise).
1154	Should only be called by an LLD if the LLD has accepted
1155	the command (i.e. queuecommand() returned or will return
1156	0). The LLD may invoke 'done' prior to queuecommand()
1157	finishing.
1158	result - should be set by LLD prior to calling 'done'. A value
1159	of 0 implies a successfully completed command (and all
1160	data (if any) has been transferred to or from the SCSI
1161	target device). 'result' is a 32 bit unsigned integer that
1162	can be viewed as 4 related bytes. The SCSI status value is
1163	in the LSB. See include/scsi/scsi.h status_byte(),
1164	msg_byte(), host_byte() and driver_byte() macros and
1165	related constants.
1166	sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
1167	should be written when the SCSI status (LSB of 'result')
1168	is set to CHECK_CONDITION (2). When CHECK_CONDITION is
1169	set, if the top nibble of sense_buffer[0] has the value 7
1170	then the mid level will assume the sense_buffer array
1171	contains a valid SCSI sense buffer; otherwise the mid
1172	level will issue a REQUEST_SENSE SCSI command to
1173	retrieve the sense buffer. The latter strategy is error
1174	prone in the presence of command queuing so the LLD should
1175	always "auto-sense".
1176	device - pointer to scsi_device object that this command is
1177	associated with.
1178	resid - an LLD should set this signed integer to the requested
1179	transfer length (i.e. 'request_bufflen') less the number
1180	of bytes that are actually transferred. 'resid' is
1181	preset to 0 so an LLD can ignore it if it cannot detect
1182	underruns (overruns should be rare). If possible an LLD
1183	should set 'resid' prior to invoking 'done'. The most
1184	interesting case is data transfers from a SCSI target
1185	device (e.g. READs) that underrun.
1186	underflow - LLD should place (DID_ERROR << 16) in 'result' if
1187	actual number of bytes transferred is less than this
1188	figure. Not many LLDs implement this check and some that
1189	do just output an error message to the log rather than
1190	report a DID_ERROR. Better for an LLD to implement
1191	'resid'.
1192
1193	It is recommended that a LLD set 'resid' on data transfers from a SCSI
1194	target device (e.g. READs). It is especially important that 'resid' is set
1195	when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
1196	(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
1197	data has been received then the safest approach is to indicate no bytes have
1198	been received. For example: to indicate that no valid data has been received
1199	a LLD might use these helpers:
1200	scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
1201	where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
1202	bytes blocks has been received 'resid' could be set like this:
1203	scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
1204
1205	The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
1206
1207
1208	Locks
1209	=====
1210	Each struct Scsi_Host instance has a spin_lock called struct
1211	Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
1212	hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
1213	is initialized to point at default_lock. Thereafter lock and unlock
1214	operations performed by the mid level use the struct Scsi_Host::host_lock
1215	pointer. Previously drivers could override the host_lock pointer but
1216	this is not allowed anymore.
1217
1218
1219	Autosense
1220	=========
1221	Autosense (or auto-sense) is defined in the SAM-2 document as "the
1222	automatic return of sense data to the application client coincident
1223	with the completion of a SCSI command" when a status of CHECK CONDITION
1224	occurs. LLDs should perform autosense. This should be done when the LLD
1225	detects a CHECK CONDITION status by either:
1226	a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
1227	to perform an extra data in phase on such responses
1228	b) or, the LLD issuing a REQUEST SENSE command itself
1229
1230	Either way, when a status of CHECK CONDITION is detected, the mid level
1231	decides whether the LLD has performed autosense by checking struct
1232	scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
1233	then autosense is assumed to have taken place. If it has another value (and
1234	this byte is initialized to 0 before each command) then the mid level will
1235	issue a REQUEST SENSE command.
1236
1237	In the presence of queued commands the "nexus" that maintains sense
1238	buffer data from the command that failed until a following REQUEST SENSE
1239	may get out of synchronization. This is why it is best for the LLD
1240	to perform autosense.
1241
1242
1243	Changes since lk 2.4 series
1244	===========================
1245	io_request_lock has been replaced by several finer grained locks. The lock
1246	relevant to LLDs is struct Scsi_Host::host_lock and there is
1247	one per SCSI host.
1248
1249	The older error handling mechanism has been removed. This means the
1250	LLD interface functions abort() and reset() have been removed.
1251	The struct scsi_host_template::use_new_eh_code flag has been removed.
1252
1253	In the 2.4 series the SCSI subsystem configuration descriptions were
1254	aggregated with the configuration descriptions from all other Linux
1255	subsystems in the Documentation/Configure.help file. In the 2.6 series,
1256	the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
1257	file that contains both configuration and help information.
1258
1259	struct SHT has been renamed to struct scsi_host_template.
1260
1261	Addition of the "hotplug initialization model" and many extra functions
1262	to support it.
1263
1264
1265	Credits
1266	=======
1267	The following people have contributed to this document:
1268	Mike Anderson <andmike at us dot ibm dot com>
1269	James Bottomley <James dot Bottomley at hansenpartnership dot com>
1270	Patrick Mansfield <patmans at us dot ibm dot com>
1271	Christoph Hellwig <hch at infradead dot org>
1272	Doug Ledford <dledford at redhat dot com>
1273	Andries Brouwer <Andries dot Brouwer at cwi dot nl>
1274	Randy Dunlap <rdunlap at xenotime dot net>
1275	Alan Stern <stern at rowland dot harvard dot edu>
1276
1277
1278	Douglas Gilbert
1279	dgilbert at interlog dot com
1280	21st September 2004

scripts/documentation-file-ref-check+1−1

@@ -12,7 +12,7 @@ use Getopt::Long qw(:config no_auto_abbrev); · 11 unmodified lines
12	# to mention a past documentation file, for example, to give credits for	12	# to mention a past documentation file, for example, to give credits for
13	# the original work.	13	# the original work.
14	my %false_positives = (	14	my %false_positives = (
15	"Documentation/scsi/scsi_mid_low_api.txt" => "Documentation/Configure.help",	15	"Documentation/scsi/scsi_mid_low_api.rst" => "Documentation/Configure.help",
16	"drivers/vhost/vhost.c" => "Documentation/virtual/lguest/lguest.c",	16	"drivers/vhost/vhost.c" => "Documentation/virtual/lguest/lguest.c",
17	);	17	);
18		18