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block: Wording tweaks to write zeroes limits

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Improve the documentation of the write zeroes limits, to mention
additional constraints that drivers should observe.  Worth squashing
into commit cf081fca, if that hadn't been pushed already :)

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2016-06-23 16:37:20 -06:00 committed by Kevin Wolf
parent 5def6b80e1
commit 29cc6a6834
1 changed files with 5 additions and 2 deletions
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7
include/block/block_int.h
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@ -331,11 +331,14 @@ typedef struct BlockLimits {
int64_t discard_alignment; int64_t discard_alignment;
/* maximum number of bytes that can zeroized at once (since it is /* maximum number of bytes that can zeroized at once (since it is
* signed, it must be < 2G, if set) */ * signed, it must be < 2G, if set), should be multiple of
* pwrite_zeroes_alignment. May be 0 if no inherent 32-bit limit */
int32_t max_pwrite_zeroes; int32_t max_pwrite_zeroes;
/* optimal alignment for write zeroes requests in bytes, must be /* optimal alignment for write zeroes requests in bytes, must be
* power of 2, and less than max_pwrite_zeroes if that is set */ * power of 2, less than max_pwrite_zeroes if that is set, and
* multiple of bs->request_alignment. May be 0 if
* bs->request_alignment is good enough */
uint32_t pwrite_zeroes_alignment; uint32_t pwrite_zeroes_alignment;
/* optimal transfer length in bytes (must be power of 2, and /* optimal transfer length in bytes (must be power of 2, and