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Without HEAD^, the following happens when you attempt a large write request to a qcow2 file such that the number of bytes covered by all clusters involved in a single allocation will exceed INT_MAX: (A) handle_alloc_space() decides to fill the whole area with zeroes and fails because bdrv_co_pwrite_zeroes() fails (the request is too large). (B) If handle_alloc_space() does not do anything, but merge_cow() decides that the requests can be merged, it will create a too long IOV that later cannot be written. (C) Otherwise, all parts will be written separately, so those requests will work. In either B or C, though, qcow2_alloc_cluster_link_l2() will have an overflow: We use an int (i) to iterate over nb_clusters, and then calculate the L2 entry based on "i << s->cluster_bits" -- which will overflow if the range covers more than INT_MAX bytes. This then leads to image corruption because the L2 entry will be wrong (it will be recognized as a compressed cluster). Even if that were not the case, the .cow_end area would be empty (because handle_alloc() will cap avail_bytes and nb_bytes at INT_MAX, so their difference (which is the .cow_end size) will be 0). So this test checks that on such large requests, the image will not be corrupted. Unfortunately, we cannot check whether COW will be handled correctly, because that data is discarded when it is written to null-co (but we have to use null-co, because writing 2 GB of data in a test is not quite reasonable). Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
10 lines
455 B
Plaintext
10 lines
455 B
Plaintext
QA output created by 270
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Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=4294967296
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wrote 512/512 bytes at offset 0
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512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4294967296 backing_file=TEST_DIR/t.IMGFMT.base data_file=TEST_DIR/t.IMGFMT.orig
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wrote 2147483136/2147483136 bytes at offset 768
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2 GiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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No errors were found on the image.
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*** done
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