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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Alberto, hi Kevin, this patch caused the iotest 024 to fail when being run with -qed: 024 fail [17:35:06] [17:35:08] 2.2s (last: 2.0s) output mismatch (see .../tests/qemu-iotests/scratch/qed-file-024/024.out.bad) --- .../qemu/tests/qemu-iotests/024.out +++ .../qemu-build/tests/qemu-iotests/scratch/qed-file-024/024.out.bad @@ -267,6 +267,7 @@ 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 +0 0x200000 TEST_DIR/subdir/t.IMGFMT +0x200000 0x200000 TEST_DIR/subdir/t.IMGFMT Could you please have a look? Thanks, Thomas PS: Thank you, Kevin, for merging the "Add more image formats to the thorough testing" patch! As you can see, it already helped to spot the first regression :-) On 11/11/2025 22.32, Kevin Wolf wrote: > From: Alberto Garcia > > 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 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3174 > Fixes: 12df580b3b7f ("qemu-img: rebase: avoid unnecessary COW operations") > Signed-off-by: Alberto Garcia > Message-ID: <20251107091834.383781-1-berto@igalia.com> > Reviewed-by: Kevin Wolf > Signed-off-by: Kevin Wolf > --- > qemu-img.c | 2 +- > tests/qemu-iotests/024 | 46 ++++++++++++++++++++++++++++++++++++++ > tests/qemu-iotests/024.out | 26 +++++++++++++++++++++ > 3 files changed, 73 insertions(+), 1 deletion(-) > > diff --git a/qemu-img.c b/qemu-img.c > index 7a32d2d16c..c42dd4e995 100644 > --- a/qemu-img.c > +++ b/qemu-img.c > @@ -4081,7 +4081,7 @@ static int img_rebase(const img_cmd_t *ccmd, int argc, char **argv) > n += offset - QEMU_ALIGN_DOWN(offset, write_align); > offset = QEMU_ALIGN_DOWN(offset, write_align); > n += QEMU_ALIGN_UP(offset + n, write_align) - (offset + n); > - n = MIN(n, size - offset); > + n = MIN(n, MIN(size - offset, IO_BUF_SIZE)); > assert(!bdrv_is_allocated(unfiltered_bs, offset, n, &n_alloc) && > n_alloc == n); > > diff --git a/tests/qemu-iotests/024 b/tests/qemu-iotests/024 > index b29c76e161..021169b4a1 100755 > --- a/tests/qemu-iotests/024 > +++ b/tests/qemu-iotests/024 > @@ -315,6 +315,52 @@ echo > > $QEMU_IMG map "$OVERLAY" | _filter_qemu_img_map > > +# Check that the region to copy to the overlay during a rebase > +# operation does not exceed the I/O buffer size. > +# > +# backing_new <-- backing_old <-- overlay > +# > +# Backing (new): -- -- -- -- <-- Empty image, size 4MB > +# Backing (old):|--|ff|ff|--| <-- 4 clusters, 1MB each > +# Overlay: |-- --|-- --| <-- 2 clusters, 2MB each > +# > +# The data at [1MB, 3MB) must be copied from the old backing image to > +# the overlay. However the rebase code will extend that region to the > +# overlay's (sub)cluster boundaries to avoid CoW (see commit 12df580b). > +# This test checks that IO_BUF_SIZE (2 MB) is taken into account. > + > +echo > +echo "=== Test that the region to copy does not exceed 2MB (IO_BUF_SIZE) ===" > +echo > + > +echo "Creating backing chain" > +echo > + > +TEST_IMG=$BASE_NEW _make_test_img 4M > +TEST_IMG=$BASE_OLD CLUSTER_SIZE=1M _make_test_img -b "$BASE_NEW" -F $IMGFMT > +TEST_IMG=$OVERLAY CLUSTER_SIZE=2M _make_test_img -b "$BASE_OLD" -F $IMGFMT > + > +echo > +echo "Writing data to region [1MB, 3MB)" > +echo > + > +$QEMU_IO "$BASE_OLD" -c "write -P 0xff 1M 2M" | _filter_qemu_io > + > +echo > +echo "Rebasing" > +echo > + > +$QEMU_IMG rebase -b "$BASE_NEW" -F $IMGFMT "$OVERLAY" > + > +echo "Verifying the data" > +echo > + > +$QEMU_IO "$OVERLAY" -c "read -P 0x00 0 1M" | _filter_qemu_io > +$QEMU_IO "$OVERLAY" -c "read -P 0xff 1M 2M" | _filter_qemu_io > +$QEMU_IO "$OVERLAY" -c "read -P 0x00 3M 1M" | _filter_qemu_io > + > +$QEMU_IMG map "$OVERLAY" | _filter_qemu_img_map > + > echo > > # success, all done > diff --git a/tests/qemu-iotests/024.out b/tests/qemu-iotests/024.out > index 3d1e31927a..1b7522ba71 100644 > --- a/tests/qemu-iotests/024.out > +++ b/tests/qemu-iotests/024.out > @@ -243,4 +243,30 @@ 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