hv_utils: Add comment about max VMbus packet size in VSS driver

The VSS driver allocates a VMbus receive buffer significantly larger than sizeof(hv_vss_msg), with no explanation. To help prevent future mistakes, add a #define and comment about why this is done. No functional change.

Michael Kelley committed 4 years ago

Commit 6de74d11 parent 4ee52452 files · +16 −2Browse files

Showing the changes to include/uapi (1 of 2 files). Show all

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include/uapi/linux/hyperv.h+11−0

@@ -90,6 +90,17 @@ struct hv_vss_check_dm_info { · 89 unmodified lines
90	__u32 flags;	90	__u32 flags;
91	} __attribute__((packed));	91	} __attribute__((packed));
92		92
		93	/*
		94	* struct hv_vss_msg encodes the fields that the Linux VSS
		95	* driver accesses. However, FREEZE messages from Hyper-V contain
		96	* additional LUN information that Linux doesn't use and are not
		97	* represented in struct hv_vss_msg. A received FREEZE message may
		98	* be as large as 6,260 bytes, so the driver must allocate at least
		99	* that much space, not sizeof(struct hv_vss_msg). Other messages
		100	* such as AUTO_RECOVER may be as large as 12,500 bytes. However,
		101	* because the Linux VSS driver responds that it doesn't support
		102	* auto-recovery, it should not receive such messages.
		103	*/
93	struct hv_vss_msg {	104	struct hv_vss_msg {
94	union {	105	union {
95	struct hv_vss_hdr vss_hdr;	106	struct hv_vss_hdr vss_hdr;