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raw: Probe required direct I/O alignment

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Add a bs->request_alignment field that contains the required
offset/length alignment for I/O requests and fill it in the raw block
drivers. Use ioctls if possible, else see what alignment it takes for
O_DIRECT to succeed.

While at it, also expose the memory alignment requirements, which may be
(and in practice are) different from the disk alignment requirements.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Paolo Bonzini 2011-11-29 12:42:20 +01:00 • committed by Kevin Wolf
parent 1b7fd72955
commit c25f53b06e
4 changed files with 132 additions and 17 deletions
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3
block.c
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@ -852,6 +852,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
bs->open_flags = flags;
bs->guest_block_size = 512;
bs->request_alignment = 512;
bs->zero_beyond_eof = true;
open_flags = bdrv_open_flags(bs, flags);
bs->read_only = !(open_flags & BDRV_O_RDWR);
@ -920,6 +921,8 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
}
bdrv_refresh_limits(bs);
assert(bdrv_opt_mem_align(bs) != 0);
assert(bs->request_alignment != 0);
#ifndef _WIN32
if (bs->is_temporary) {