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/linux/hyperv.h (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	90	__u32 flags;
91	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	104	struct hv_vss_msg {
94	105	union {
95	106	struct hv_vss_hdr vss_hdr;