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From c0c1147350005b47068285a288f848cf75eb60c6 Mon Sep 17 00:00:00 2001
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From: Christoph Hellwig <hch@lst.de>
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Date: Tue, 26 Jan 2010 14:49:08 +0100
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Subject: [PATCH] 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
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back EINVAL from the kernel which translate to I/O errors for the guest.
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Add a MAX_IOV defintion for platforms that don't have it. For now we use
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the same 1024 define that's used on Linux and various other platforms,
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but until the windows block backend implements some kind of vectored I/O
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it doesn't matter.
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Signed-off-by: Christoph Hellwig <hch@lst.de>
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Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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---
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block.c | 4 ++++
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qemu-common.h | 4 ++++
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2 files changed, 8 insertions(+), 0 deletions(-)
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diff --git a/block.c b/block.c
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index 97af3f5..9697dc9 100644
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--- a/block.c
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+++ b/block.c
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@@ -1669,6 +1669,10 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs,
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merge = bs->drv->bdrv_merge_requests(bs, &reqs[outidx], &reqs[i]);
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}
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+ if (reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1 > IOV_MAX) {
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+ merge = 0;
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+ }
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+
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if (merge) {
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size_t size;
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QEMUIOVector *qiov = qemu_mallocz(sizeof(*qiov));
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diff --git a/qemu-common.h b/qemu-common.h
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index 1c5c0b2..b604ddf 100644
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--- a/qemu-common.h
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+++ b/qemu-common.h
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@@ -54,6 +54,10 @@ struct iovec {
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void *iov_base;
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size_t iov_len;
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};
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+/*
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+ * Use the same value as Linux for now.
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+ */
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+#define IOV_MAX 1024
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#else
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#include <sys/uio.h>
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#endif
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--
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1.6.6.1
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