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909852ba6b4a22fd2b6f9d8b88adb5fc47dfa781
qemu-qemu/tests/qemu-iotests/024.out
Alberto Garcia 909852ba6b qemu-img rebase: don't exceed IO_BUF_SIZE in one operation 
During a rebase operation data is copied from the backing chain into
the target image using a loop, and each iteration looks for a
contiguous region of allocated data of at most IO_BUF_SIZE (2 MB).

Once that region is found, and in order to avoid partial writes, its
boundaries are extended so they are aligned to the (sub)clusters of
the target image (see commit 12df580b).

This operation can however result in a region that exceeds the maximum
allowed IO_BUF_SIZE, crashing qemu-img.

This can be easily reproduced when the source image has a smaller
cluster size than the target image:

base <- int <- active

$ qemu-img create -f qcow2 base.qcow2 4M
$ qemu-img create -f qcow2 -F qcow2 -b base.qcow2 -o cluster_size=1M int.qcow2
$ qemu-img create -f qcow2 -F qcow2 -b int.qcow2  -o cluster_size=2M active.qcow2
$ qemu-io -c "write -P 0xff 1M 2M" int.qcow2
$ qemu-img rebase -F qcow2 -b base.qcow2 active.qcow2
qemu-img: qemu-img.c:4102: img_rebase: Assertion `written + pnum <= IO_BUF_SIZE' failed.
Aborted

Cc: qemu-stable <qemu-stable@nongnu.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3174
Fixes: 12df580b3b ("qemu-img: rebase: avoid unnecessary COW operations")
Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-ID: <20251107091834.383781-1-berto@igalia.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2025-11-11 22:06:09 +01:00

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QA output created by 024
Creating backing file
Formatting 'TEST_DIR/t.IMGFMT.base_old', fmt=IMGFMT size=1073741824
=== IO: pattern 0x11
wrote 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 131072
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 393216
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 524288
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 655360
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 786432
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 917504
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Creating new backing file
Formatting 'TEST_DIR/t.IMGFMT.base_new', fmt=IMGFMT size=1073741824
=== IO: pattern 0x22
wrote 131072/131072 bytes at offset 0
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 131072/131072 bytes at offset 262144
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 131072/131072 bytes at offset 524288
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 131072/131072 bytes at offset 786432
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Creating COW image
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base_old backing_fmt=IMGFMT
=== IO: pattern 0x33
wrote 262144/262144 bytes at offset 0
256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
wrote 262144/262144 bytes at offset 524288
256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Read before the rebase to make sure everything is set up correctly
=== IO: pattern 0x33
read 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 65536
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 131072
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 196608
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 327680
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 393216
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 458752
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 524288
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 589824
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 655360
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 720896
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 786432
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 851968
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 917504
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 983040
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Rebase and test again
=== IO: pattern 0x33
read 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 65536
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 131072
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 196608
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 327680
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 393216
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 458752
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 524288
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 589824
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 655360
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x33
read 65536/65536 bytes at offset 720896
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 786432
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 851968
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x11
read 65536/65536 bytes at offset 917504
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== IO: pattern 0x00
read 65536/65536 bytes at offset 983040
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== Test rebase in a subdirectory of the working directory ===
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=1048576
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=1048576
Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=1048576 backing_file=t.IMGFMT.base_old backing_fmt=IMGFMT
wrote 131072/131072 bytes at offset 0
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 196608
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 131072/131072 bytes at offset 65536
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 196608
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
backing file: t.IMGFMT.base_new (actual path: TEST_DIR/subdir/t.IMGFMT.base_new)
read 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 65536
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 131072
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 196608
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Offset Length File
0 0x30000 TEST_DIR/subdir/t.IMGFMT
0x30000 0x10000 TEST_DIR/subdir/t.IMGFMT.base_new
=== Test rebase within one backing chain ===
Creating backing chain
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=327680
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=262144 backing_file=TEST_DIR/subdir/t.IMGFMT.base_new backing_fmt=IMGFMT
Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=327680 backing_file=TEST_DIR/subdir/t.IMGFMT.base_old backing_fmt=IMGFMT
Fill backing files with data
wrote 327680/327680 bytes at offset 0
320 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 262144/262144 bytes at offset 0
256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Check the last cluster is zeroed in overlay before the rebase
read 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Rebase onto another image in the same chain
Verify that data is read the same before and after rebase
read 262144/262144 bytes at offset 0
256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
=== Test rebase with different cluster sizes ===
Creating backing chain
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=393216
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=393216 backing_file=TEST_DIR/subdir/t.IMGFMT.base_new backing_fmt=IMGFMT
Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=393216 backing_file=TEST_DIR/subdir/t.IMGFMT.base_old backing_fmt=IMGFMT
image: TEST_DIR/subdir/t.IMGFMT
file format: IMGFMT
virtual size: 384 KiB (393216 bytes)
cluster_size: 131072
backing file: TEST_DIR/subdir/t.IMGFMT.base_old
Fill backing files with data
wrote 65536/65536 bytes at offset 65536
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Rebase onto another image in the same chain
Verify that data is read the same before and after rebase
read 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 65536
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 131072/131072 bytes at offset 131072
128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 262144
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 65536/65536 bytes at offset 327680
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Verify that untouched cluster remains unallocated
Offset Length File
0 0x20000 TEST_DIR/subdir/t.IMGFMT
0x40000 0x20000 TEST_DIR/subdir/t.IMGFMT
=== Test that the region to copy does not exceed 2MB (IO_BUF_SIZE) ===
Creating backing chain
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=4194304
Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=4194304 backing_file=TEST_DIR/subdir/t.IMGFMT.base_new backing_fmt=IMGFMT
Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=4194304 backing_file=TEST_DIR/subdir/t.IMGFMT.base_old backing_fmt=IMGFMT
Writing data to region [1MB, 3MB)
wrote 2097152/2097152 bytes at offset 1048576
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Rebasing
Verifying the data
read 1048576/1048576 bytes at offset 0
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 2097152/2097152 bytes at offset 1048576
2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
read 1048576/1048576 bytes at offset 3145728
1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Offset Length File
0 0x400000 TEST_DIR/subdir/t.IMGFMT
*** done
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