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author | 2010-05-19 20:53:10 +0200 | |
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committer | 2010-07-20 17:28:17 -0500 | |
commit | fb0bd59720c4010f9dd5fb7627ed3bc3d137b25d (patch) | |
tree | 9ba12b8fd344b0c4a76306e2292e8c2decf0fa15 | |
parent | pci: irq_state vmstate breakage (diff) | |
download | qemu-kvm-fb0bd59720c4010f9dd5fb7627ed3bc3d137b25d.tar.gz qemu-kvm-fb0bd59720c4010f9dd5fb7627ed3bc3d137b25d.tar.bz2 qemu-kvm-fb0bd59720c4010f9dd5fb7627ed3bc3d137b25d.zip |
block: fix sector comparism in multiwrite_req_compare
The difference between the start sectors of two requests can be larger
than the size of the "int" type, which can lead to a not correctly
sorted multiwrite array and thus spurious I/O errors and filesystem
corruption due to incorrect request merges.
So instead of doing the cute sector arithmetics trick spell out the
exact comparisms.
Spotted by Kevin Wolf based on a testcase from Michael Tokarev.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 77be4366baface6613cfc312ba281f8e5860997c)
-rw-r--r-- | block.c | 14 |
1 files changed, 13 insertions, 1 deletions
@@ -1636,7 +1636,19 @@ static void multiwrite_cb(void *opaque, int ret) static int multiwrite_req_compare(const void *a, const void *b) { - return (((BlockRequest*) a)->sector - ((BlockRequest*) b)->sector); + const BlockRequest *req1 = a, *req2 = b; + + /* + * Note that we can't simply subtract req2->sector from req1->sector + * here as that could overflow the return value. + */ + if (req1->sector > req2->sector) { + return 1; + } else if (req1->sector < req2->sector) { + return -1; + } else { + return 0; + } } /* |