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Date: Tue, 19 Jan 2010 22:15:39 +0100
From: Christoph Hellwig <hch@lst.de>
Message-ID: <20100119211539.GA4383@lst.de>
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Subject: [Qemu-devel] [PATCH] block: prevent multiwrite_merge from creating
	too large iovecs
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To: qemu-devel@nongnu.org

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.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: qemu/block.c
===================================================================
--- qemu.orig/block.c	2010-01-19 22:10:19.797003226 +0100
+++ qemu/block.c	2010-01-19 22:11:08.226005767 +0100
@@ -1711,6 +1711,10 @@ static int multiwrite_merge(BlockDriverS
             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));