From 29cc6a6834add5cddbc391d07c1b3ace2ad9b8eb Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 23 Jun 2016 16:37:20 -0600 Subject: [PATCH] block: Wording tweaks to write zeroes limits 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 Reviewed-by: Fam Zheng Signed-off-by: Kevin Wolf --- include/block/block_int.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/block/block_int.h b/include/block/block_int.h index 7d2b152779..7a4a00fdfc 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -331,11 +331,14 @@ typedef struct BlockLimits { int64_t discard_alignment; /* 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; /* 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; /* optimal transfer length in bytes (must be power of 2, and