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block: add BlockLimits.max_iov field

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The maximum number of struct iovec elements depends on the
BlockDriverState.  The raw-posix and iSCSI protocols have a maximum of
IOV_MAX but others could have different values.

Cc: Peter Lieven <pl@kamp.de>
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2015-07-09 10:56:44 +01:00
parent 49cffbc607
commit bd44feb754
2 changed files with 10 additions and 0 deletions
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7
block/io.c
View File

@ -166,9 +166,13 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
bs->bl.max_transfer_length = bs->file->bs->bl.max_transfer_length;
bs->bl.min_mem_alignment = bs->file->bs->bl.min_mem_alignment;
bs->bl.opt_mem_alignment = bs->file->bs->bl.opt_mem_alignment;
bs->bl.max_iov = bs->file->bs->bl.max_iov;
} else {
bs->bl.min_mem_alignment = 512;
bs->bl.opt_mem_alignment = getpagesize();
/* Safe default since most protocols use readv()/writev()/etc */
bs->bl.max_iov = IOV_MAX;
}
if (bs->backing) {
@ -189,6 +193,9 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
bs->bl.min_mem_alignment =
MAX(bs->bl.min_mem_alignment,
bs->backing->bs->bl.min_mem_alignment);
bs->bl.max_iov =
MIN(bs->bl.max_iov,
bs->backing->bs->bl.max_iov);
}
/* Then let the driver override it */

3
include/block/block_int.h
View File

@ -330,6 +330,9 @@ typedef struct BlockLimits {
/* memory alignment for bounce buffer */
size_t opt_mem_alignment;
/* maximum number of iovec elements */
int max_iov;
} BlockLimits;
typedef struct BdrvOpBlocker BdrvOpBlocker;