03.12.2018 13:14, Anton Nefedov wrote: > If COW areas of the newly allocated clusters are zeroes on the backing image, > efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) can be used on the whole > cluster instead of writing explicit zero buffers later in perform_cow(). > > iotest 060: > write to the discarded cluster does not trigger COW anymore. > Use a backing image instead. >
[..] > --- a/tests/qemu-iotests/060 > +++ b/tests/qemu-iotests/060 > @@ -150,27 +150,33 @@ $QEMU_IO -c "$OPEN_RO" -c "read -P 1 0 512" | > _filter_qemu_io > echo > echo "=== Testing overlap while COW is in flight ===" > echo > +BACKING_IMG=$TEST_IMG.base > +TEST_IMG=$BACKING_IMG _make_test_img 1G > + > +$QEMU_IO -c 'write 64k 64k' "$BACKING_IMG" | _filter_qemu_io > + > # compat=0.10 is required in order to make the following discard actually > -# unallocate the sector rather than make it a zero sector - we want COW, > after > -# all. > -IMGOPTS='compat=0.10' _make_test_img 1G > +# unallocate the sector rather than make it a zero sector as we would like > +# to reuse it for another guest offset > +IMGOPTS='compat=0.10' _make_test_img -b "$BACKING_IMG" 1G > # Write two clusters, the second one enforces creation of an L2 table after > # the first data cluster. > $QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io > -# Discard the first cluster. This cluster will soon enough be reallocated and > -# used for COW. > +# Discard the first cluster. This cluster will soon enough be reallocated > $QEMU_IO -c 'discard 0k 64k' "$TEST_IMG" | _filter_qemu_io > # Now, corrupt the image by marking the second L2 table cluster as free. > poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c > -# Start a write operation requiring COW on the image stopping it right before > -# doing the read; then, trigger the corruption prevention by writing > anything to > -# any unallocated cluster, leading to an attempt to overwrite the second L2 > +# Start a write operation requiring COW on the image; > +# this write will reuse the host offset released by a previous discard. > +# Stop it right before doing the read. > +# Then, trigger the corruption prevention by writing anything to > +# another unallocated cluster, leading to an attempt to overwrite the second > L2 > # table. Finally, resume the COW write and see it fail (but not crash). > echo "open -o file.driver=blkdebug $TEST_IMG > break cow_read 0 > -aio_write 0k 1k > +aio_write 64k 1k > wait_break 0 > -write 64k 64k > +write 128k 64k don't understand why you need these changes. works for me, without them, if write to backing at 0 offset, of course. As I understand, discard create unallocated holes in top qcow2 for old qcow2 version. > resume 0" | $QEMU_IO | _filter_qemu_io > > echo > diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out > index d67c6234a4..ec8f15d2f0 100644 > --- a/tests/qemu-iotests/060.out > +++ b/tests/qemu-iotests/060.out > @@ -97,7 +97,10 @@ read 512/512 bytes at offset 0 > > === Testing overlap while COW is in flight === > > -Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 > +Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1073741824 > +wrote 65536/65536 bytes at offset 65536 > +64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) > +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 > backing_file=TEST_DIR/t.IMGFMT.base > 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 536870912 > -- Best regards, Vladimir
