virtio-blk: the nature of discard_sector_alignment

[Jakub Jermar <jakub.jermar@kernkonzept.com>]

Hello,

my device enforces the discard_sector_alignment on the request (both
sector and num_sectors), but for some reason the blkdiscard command and
Linux driver issue requests that do not honor this alignment.

Does discard_sector_alignment represent a strict requirement that must
be always honored or is it rather a hint to the driver? The wording in
the spec seems to be more lenient while in Linux the field is documented
rather strictly:

/* Discard commands must be aligned to this number of sectors. */
__u32 discard_sector_alignment;

Also, is it reasonable to assume that discard_sector_alignment should be
enforced also on request's num_sectors. It seems to me like one can
theoretically have requests that have num_sectors aligned to
sector-size, but not to discard_sector_alignment.

Thanks in advance,
Jakub

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