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block: avoid creating too large iovecs in multiwrite_merge

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If we go over the maximum number of iovecs support by syscall we get
back EINVAL from the kernel which translate to I/O errors for the guest.

Add a MAX_IOV defintion for platforms that don't have it.  For now we use
the same 1024 define that's used on Linux and various other platforms,
but until the windows block backend implements some kind of vectored I/O
it doesn't matter.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Christoph Hellwig 2010-01-26 14:49:08 +01:00 committed by Anthony Liguori
parent 6185c5783c
commit e2a305fb13
2 changed files with 8 additions and 0 deletions
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4
block.c
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@ -1691,6 +1691,10 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
merge = bs->drv->bdrv_merge_requests(bs, &reqs[outidx], &reqs[i]);
}
if (reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1 > IOV_MAX) {
merge = 0;
}
if (merge) {
size_t size;
QEMUIOVector *qiov = qemu_mallocz(sizeof(*qiov));

4
qemu-common.h
View file

@ -54,6 +54,10 @@ struct iovec {
void *iov_base;
size_t iov_len;
};
/*
* Use the same value as Linux for now.
*/
#define IOV_MAX 1024
#else
#include <sys/uio.h>
#endif