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block: Inherit opt_transfer_length

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When there is a format driver between the backend, it's not guaranteed
that exposing the opt_transfer_length for the format driver results in
the optimal requests (because of fragmentation etc.), but it can't make
things worse, so let's just do it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoît Canet <benoit@irqsave.net>
This commit is contained in:
Kevin Wolf 2013-12-11 19:50:32 +01:00
parent d34682cd4a
commit 466ad822de
1 changed files with 19 additions and 1 deletions
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20
block.c
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@ -489,7 +489,25 @@ static int bdrv_refresh_limits(BlockDriverState *bs)
memset(&bs->bl, 0, sizeof(bs->bl));
if (drv && drv->bdrv_refresh_limits) {
if (!drv) {
return 0;
}
/* Take some limits from the children as a default */
if (bs->file) {
bdrv_refresh_limits(bs->file);
bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
}
if (bs->backing_hd) {
bdrv_refresh_limits(bs->backing_hd);
bs->bl.opt_transfer_length =
MAX(bs->bl.opt_transfer_length,
bs->backing_hd->bl.opt_transfer_length);
}
/* Then let the driver override it */
if (drv->bdrv_refresh_limits) {
return drv->bdrv_refresh_limits(bs);
}