From 6de74d1069b821e96460d0fc2edfc35785db04fb Mon Sep 17 00:00:00 2001 From: Michael Kelley Date: Wed, 9 Feb 2022 08:11:10 -0800 Subject: 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. Signed-off-by: Michael Kelley Link: https://lore.kernel.org/r/1644423070-75125-1-git-send-email-mikelley@microsoft.com Signed-off-by: Wei Liu --- include/uapi/linux/hyperv.h | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'include') diff --git a/include/uapi/linux/hyperv.h b/include/uapi/linux/hyperv.h index daf82a230c0e..aaa502a7bff4 100644 --- a/include/uapi/linux/hyperv.h +++ b/include/uapi/linux/hyperv.h @@ -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; -- cgit v1.2.3