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

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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.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1644423070-75125-1-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
This commit is contained in:
Michael Kelley 2022-02-09 08:11:10 -08:00 • committed by Wei Liu
parent 4ee5245871
commit 6de74d1069
2 changed files with 16 additions and 2 deletions
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11
include/uapi/linux/hyperv.h
View file

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