Changes since 2.5.0: ---[recommended] New helpers: sb_bread(), sb_getblk(), sb_find_get_block(), set_bh(),	sb_set_blocksize() and sb_min_blocksize(). Use them. (sb_find_get_block() replaces 2.4's get_hash_table()) ---[recommended] New methods: ->alloc_inode() and ->destroy_inode(). Remove inode->u.foo_inode_iDeclare	struct foo_inode_info {		/* fs-private stuff */		struct inode vfs_inode;	};	static inline struct foo_inode_info *FOO_I(struct inode *inode)	{		return list_entry(inode, struct foo_inode_info, vfs_inode);	} Use FOO_I(inode) instead of &inode->u.foo_inode_i; Add foo_alloc_inode() and foo_destroy_inode() - the former should allocatefoo_inode_info and return the address of ->vfs_inode, the latter should freeFOO_I(inode) (see in-tree filesystems for examples). Make them ->alloc_inode and ->destroy_inode in your super_operations. Keep in mind that now you need explicit initialization of private datatypically between calling iget_locked() and unlocking the inode. At some point that will become mandatory. ---[mandatory] Change of file_system_type method (->read_super to ->get_sb) ->read_super() is no more.  Ditto for DECLARE_FSTYPE and DECLARE_FSTYPE_DEV. Turn your foo_read_super() into a function that would return 0 in case ofsuccess and negative number in case of error (-EINVAL unless you have moreinformative error value to report).  Call it foo_fill_super().  Now declare int foo_get_sb(struct file_system_type *fs_type,	int flags, const char *dev_name, void *data, struct vfsmount *mnt){	return get_sb_bdev(fs_type, flags, dev_name, data, foo_fill_super,			   mnt);} (or similar with s/bdev/nodev/ or s/bdev/single/, depending on the kind offilesystem). Replace DECLARE_FSTYPE... with explicit initializer and have ->get_sb set asfoo_get_sb. ---[mandatory] Locking change: ->s_vfs_rename_sem is taken only by cross-directory renames.Most likely there is no need to change anything, but if you relied onglobal exclusion between renames for some internal purpose - you need tochange your internal locking.  Otherwise exclusion warranties remain thesame (i.e. parents and victim are locked, etc.). ---[informational] Now we have the exclusion between ->lookup() and directory removal (by->rmdir() and ->rename()).  If you used to need that exclusion and doit by internal locking (most of filesystems couldn't care less) - youcan relax your locking. ---[mandatory] ->lookup(), ->truncate(), ->create(), ->unlink(), ->mknod(), ->mkdir(),->rmdir(), ->link(), ->lseek(), ->symlink(), ->rename()and ->readdir() are called without BKL now.  Grab it on entry, drop upon return- that will guarantee the same locking you used to have.  If your method or itsparts do not need BKL - better yet, now you can shift lock_kernel() andunlock_kernel() so that they would protect exactly what needs to beprotected. ---[mandatory] BKL is also moved from around sb operations.  ->write_super() Is now called without BKL held.  BKL should have been shifted into individual fs sb_opfunctions.  If you don't need it, remove it.   ---[informational] check for ->link() target not being a directory is done by callers.  Feelfree to drop it... ---[informational] ->link() callers hold ->i_mutex on the object we are linking to.  Some of yourproblems might be over... ---[mandatory] new file_system_type method - kill_sb(superblock).  If you are convertingan existing filesystem, set it according to ->fs_flags:	FS_REQUIRES_DEV		-	kill_block_super	FS_LITTER		-	kill_litter_super	neither			-	kill_anon_superFS_LITTER is gone - just remove it from fs_flags. ---[mandatory] 	FS_SINGLE is gone (actually, that had happened back when ->get_sb()went in - and hadn't been documented ;-/).  Just remove it from fs_flags(and see ->get_sb() entry for other actions). ---[mandatory] ->setattr() is called without BKL now.  Caller _always_ holds ->i_mutex, sowatch for ->i_mutex-grabbing code that might be used by your ->setattr().Callers of notify_change() need ->i_mutex now. ---[recommended] New super_block field "struct export_operations *s_export_op" forexplicit support for exporting, e.g. via NFS.  The structure is fullydocumented at its declaration in include/linux/fs.h, and inDocumentation/filesystems/nfs/Exporting. Briefly it allows for the definition of decode_fh and encode_fh operationsto encode and decode filehandles, and allows the filesystem to usea standard helper function for decode_fh, and provide file-system specificsupport for this helper, particularly get_parent. It is planned that this will be required for exporting once the codesettles down a bit. [mandatory] s_export_op is now required for exporting a filesystem.isofs, ext2, ext3, resierfs, fatcan be used as examples of very different filesystems. ---[mandatory] iget4() and the read_inode2 callback have been superseded by iget5_locked()which has the following prototype,     struct inode *iget5_locked(struct super_block *sb, unsigned long ino,				int (*test)(struct inode *, void *),				int (*set)(struct inode *, void *),				void *data); 'test' is an additional function that can be used when the inodenumber is not sufficient to identify the actual file object. 'set'should be a non-blocking function that initializes those parts of anewly created inode to allow the test function to succeed. 'data' ispassed as an opaque value to both test and set functions. When the inode has been created by iget5_locked(), it will be returned with theI_NEW flag set and will still be locked.  The filesystem then needs to finalizethe initialization. Once the inode is initialized it must be unlocked bycalling unlock_new_inode(). The filesystem is responsible for setting (and possibly testing) i_inowhen appropriate. There is also a simpler iget_locked function thatjust takes the superblock and inode number as arguments and does thetest and set for you. e.g.	inode = iget_locked(sb, ino);	if (inode->i_state & I_NEW) {		err = read_inode_from_disk(inode);		if (err < 0) {			iget_failed(inode);			return err;		}		unlock_new_inode(inode);	} Note that if the process of setting up a new inode fails, then iget_failed()should be called on the inode to render it dead, and an appropriate errorshould be passed back to the caller. ---[recommended] ->getattr() finally getting used.  See instances in nfs, minix, etc. ---[mandatory] ->revalidate() is gone.  If your filesystem had it - provide ->getattr()and let it call whatever you had as ->revlidate() + (for symlinks thathad ->revalidate()) add calls in ->follow_link()/->readlink(). ---[mandatory] ->d_parent changes are not protected by BKL anymore.  Read access is safeif at least one of the following is true:	* filesystem has no cross-directory rename()	* we know that parent had been locked (e.g. we are looking at->d_parent of ->lookup() argument).	* we are called from ->rename().	* the child's ->d_lock is heldAudit your code and add locking if needed.  Notice that any place that isnot protected by the conditions above is risky even in the old tree - youhad been relying on BKL and that's prone to screwups.  Old tree had quitea few holes of that kind - unprotected access to ->d_parent leading toanything from oops to silent memory corruption. ---[mandatory] 	FS_NOMOUNT is gone.  If you use it - just set MS_NOUSER in flags(see rootfs for one kind of solution and bdev/socket/pipe for another). ---[recommended] 	Use bdev_read_only(bdev) instead of is_read_only(kdev).  The latteris still alive, but only because of the mess in drivers/s390/block/dasd.c.As soon as it gets fixed is_read_only() will die. ---[mandatory] ->permission() is called without BKL now. Grab it on entry, drop uponreturn - that will guarantee the same locking you used to have.  Ifyour method or its parts do not need BKL - better yet, now you canshift lock_kernel() and unlock_kernel() so that they would protectexactly what needs to be protected. ---[mandatory] ->statfs() is now called without BKL held.  BKL should have beenshifted into individual fs sb_op functions where it's not clear thatit's safe to remove it.  If you don't need it, remove it. ---[mandatory] 	is_read_only() is gone; use bdev_read_only() instead. ---[mandatory] 	destroy_buffers() is gone; use invalidate_bdev(). ---[mandatory] 	fsync_dev() is gone; use fsync_bdev().  NOTE: lvm breakage isdeliberate; as soon as struct block_device * is propagated in a reasonableway by that code fixing will become trivial; until then nothing can bedone. [mandatory] 	block truncatation on error exit from ->write_begin, and ->direct_IOmoved from generic methods (block_write_begin, cont_write_begin,nobh_write_begin, blockdev_direct_IO*) to callers.  Take a look atext2_write_failed and callers for an example. [mandatory] 	->truncate is going away.  The whole truncate sequence needs to beimplemented in ->setattr, which is now mandatory for filesystemsimplementing on-disk size changes.  Start with a copy of the old inode_setattrand vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence tobe in order of zeroing blocks using block_truncate_page or similar helpers,size update and on finally on-disk truncation which should not fail.inode_change_ok now includes the size checks for ATTR_SIZE and must be calledin the beginning of ->setattr unconditionally. [mandatory] 	->clear_inode() and ->delete_inode() are gone; ->evict_inode() shouldbe used instead.  It gets called whenever the inode is evicted, whether it hasremaining links or not.  Caller does *not* evict the pagecache or inode-associatedmetadata buffers; getting rid of those is responsibility of method, as it hadbeen for ->delete_inode(). Caller makes sure async writeback cannot be runningfor the inode while (or after) ->evict_inode() is called. 	->drop_inode() returns int now; it's called on final iput() withinode->i_lock held and it returns true if filesystems wants the inode to bedropped.  As before, generic_drop_inode() is still the default and it's beenupdated appropriately.  generic_delete_inode() is also alive and it consistssimply of return 1.  Note that all actual eviction work is done by caller after->drop_inode() returns. 	As before, clear_inode() must be called exactly once on each call of->evict_inode() (as it used to be for each call of ->delete_inode()).  Unlikebefore, if you are using inode-associated metadata buffers (i.e.mark_buffer_dirty_inode()), it's your responsibility to callinvalidate_inode_buffers() before clear_inode(). 	NOTE: checking i_nlink in the beginning of ->write_inode() and bailing outif it's zero is not *and* *never* *had* *been* enough.  Final unlink() and iput()may happen while the inode is in the middle of ->write_inode(); e.g. if you blindlyfree the on-disk inode, you may end up doing that while ->write_inode() is writingto it. ---[mandatory] 	.d_delete() now only advises the dcache as to whether or not to cacheunreferenced dentries, and is now only called when the dentry refcount goes to0. Even on 0 refcount transition, it must be able to tolerate being called 0,1, or more times (eg. constant, idempotent). ---[mandatory] 	.d_compare() calling convention and locking rules are significantlychanged. Read updated documentation in Documentation/filesystems/vfs.txt (andlook at examples of other filesystems) for guidance. ---[mandatory] 	.d_hash() calling convention and locking rules are significantlychanged. Read updated documentation in Documentation/filesystems/vfs.txt (andlook at examples of other filesystems) for guidance. ---[mandatory]	dcache_lock is gone, replaced by fine grained locks. See fs/dcache.cfor details of what locks to replace dcache_lock with in order to protectparticular things. Most of the time, a filesystem only needs ->d_lock, whichprotects *all* the dcache state of a given dentry. --[mandatory] 	Filesystems must RCU-free their inodes, if they can have been accessedvia rcu-walk path walk (basically, if the file can have had a path name in thevfs namespace). 	i_dentry and i_rcu share storage in a union, and the vfs expectsi_dentry to be reinitialized before it is freed, so an:   INIT_LIST_HEAD(&inode->i_dentry); must be done in the RCU callback. --[recommended]	vfs now tries to do path walking in "rcu-walk mode", which avoidsatomic operations and scalability hazards on dentries and inodes (seeDocumentation/filesystems/path-lookup.txt). d_hash and d_compare changes(above) are examples of the changes required to support this. For more complexfilesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, sono changes are required to the filesystem. However, this is costly and losesthe benefits of rcu-walk mode. We will begin to add filesystem callbacks thatare rcu-walk aware, shown below. Filesystems should take advantage of thiswhere possible. --[mandatory]	d_revalidate is a callback that is made on every path element (ifthe filesystem provides it), which requires dropping out of rcu-walk mode. Thismay now be called in rcu-walk mode (nd->flags & LOOKUP_RCU). -ECHILD should bereturned if the filesystem cannot handle rcu-walk. SeeDocumentation/filesystems/vfs.txt for more details. 	permission and check_acl are inode permission checks that are calledon many or all directory inodes on the way down a path walk (to check forexec permission). These must now be rcu-walk aware (flags & IPERM_FLAG_RCU).See Documentation/filesystems/vfs.txt for more details. --[mandatory]	In ->fallocate() you must check the mode option passed in.  If yourfilesystem does not support hole punching (deallocating space in the middle of afile) you must return -EOPNOTSUPP if FALLOC_FL_PUNCH_HOLE is set in mode.Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,so the i_size should not change when hole punching, even when puching the end ofa file off. --[mandatory]	->get_sb() is gone.  Switch to use of ->mount().  Typically it's justa matter of switching from calling get_sb_... to mount_... and changing thefunction type.  If you were doing it manually, just switch from setting ->mnt_rootto some pointer to returning that pointer.  On errors return ERR_PTR(...). --[mandatory]	->permission() and generic_permission()have lost flagsargument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.	generic_permission() has also lost the check_acl argument; ACL checkinghas been taken to VFS and filesystems need to provide a non-NULL ->i_op->get_aclto read an ACL from disk. --[mandatory]	If you implement your own ->llseek() you must handle SEEK_HOLE andSEEK_DATA.  You can hanle this by returning -EINVAL, but it would be nicer tosupport it in some way.  The generic handler assumes that the entire file isdata and there is a virtual hole at the end of the file.  So if the providedoffset is less than i_size and SEEK_DATA is specified, return the same offset.If the above is true for the offset and you are given SEEK_HOLE, return the endof the file.  If the offset is i_size or greater return -ENXIO in either case. [mandatory]	If you have your own ->fsync() you must make sure to callfilemap_write_and_wait_range() so that all dirty pages are synced out properly.You must also keep in mind that ->fsync() is not called with i_mutex heldanymore, so if you require i_mutex locking you must make sure to take it andrelease it yourself. --[mandatory]	d_alloc_root() is gone, along with a lot of bugs caused by codemisusing it.  Replacement: d_make_root(inode).  The difference is,d_make_root() drops the reference to inode if dentry allocation fails.