When opening an image with discard=off, we punch hole in the image when writing zeroes, making the image sparse. This breaks users that want to ensure that writes cannot fail with ENOSPACE by using fully allocated images[1].
bdrv_co_pwrite_zeroes() correctly disables BDRV_REQ_MAY_UNMAP if we opened the child without discard=unmap or discard=on. But we don't go through this function when accessing the top node. Move the check down to bdrv_co_do_pwrite_zeroes() which seems to be used in all code paths. This change implements the documented behavior, punching holes only when opening the image with discard=on or discard=unmap. This may not be the best default but can improve it later. The test depends on a file system supporting discard, deallocating the entire file when punching hole with the length of the entire file. Tested with xfs, ext4, and tmpfs. [1] https://lists.nongnu.org/archive/html/qemu-discuss/2024-06/msg00003.html Signed-off-by: Nir Soffer <nsof...@redhat.com> --- block/io.c | 9 +- tests/qemu-iotests/tests/write-zeroes-unmap | 127 ++++++++++++++++++ .../qemu-iotests/tests/write-zeroes-unmap.out | 81 +++++++++++ 3 files changed, 213 insertions(+), 4 deletions(-) create mode 100755 tests/qemu-iotests/tests/write-zeroes-unmap create mode 100644 tests/qemu-iotests/tests/write-zeroes-unmap.out diff --git a/block/io.c b/block/io.c index 7217cf811b..301514c880 100644 --- a/block/io.c +++ b/block/io.c @@ -1860,10 +1860,15 @@ bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes, /* By definition there is no user buffer so this flag doesn't make sense */ if (flags & BDRV_REQ_REGISTERED_BUF) { return -EINVAL; } + /* If opened with discard=off we should never unmap. */ + if (!(bs->open_flags & BDRV_O_UNMAP)) { + flags &= ~BDRV_REQ_MAY_UNMAP; + } + /* Invalidate the cached block-status data range if this write overlaps */ bdrv_bsc_invalidate_range(bs, offset, bytes); assert(alignment % bs->bl.request_alignment == 0); head = offset % alignment; @@ -2313,14 +2318,10 @@ int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild *child, int64_t offset, { IO_CODE(); trace_bdrv_co_pwrite_zeroes(child->bs, offset, bytes, flags); assert_bdrv_graph_readable(); - if (!(child->bs->open_flags & BDRV_O_UNMAP)) { - flags &= ~BDRV_REQ_MAY_UNMAP; - } - return bdrv_co_pwritev(child, offset, bytes, NULL, BDRV_REQ_ZERO_WRITE | flags); } /* diff --git a/tests/qemu-iotests/tests/write-zeroes-unmap b/tests/qemu-iotests/tests/write-zeroes-unmap new file mode 100755 index 0000000000..7cfeeaf839 --- /dev/null +++ b/tests/qemu-iotests/tests/write-zeroes-unmap @@ -0,0 +1,127 @@ +#!/usr/bin/env bash +# group: quick +# +# Test write zeros unmap. +# +# Copyright (C) Red Hat, Inc. +# +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 2 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. +# + +seq="$(basename $0)" +echo "QA output created by $seq" + +trap _cleanup_test_img exit + +# get standard environment, filters and checks +cd .. +. ./common.rc +. ./common.filter + +_supported_fmt raw +_supported_proto file +_supported_os Linux + +create_test_image() { + _make_test_img -f $IMGFMT 1m +} + +filter_command() { + _filter_testdir | _filter_qemu_io | _filter_qemu | _filter_hmp +} + +print_disk_usage() { + du -sh $TEST_IMG | _filter_testdir +} + +echo +echo "=== defaults - write zeros ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -z 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \ + | filter_command +print_disk_usage + +echo +echo "=== defaults - write zeros unmap ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \ + | filter_command +print_disk_usage + + +echo +echo "=== defaults - write actual zeros ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \ + | filter_command +print_disk_usage + +echo +echo "=== discard=off - write zeroes unmap ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=off \ + | filter_command +print_disk_usage + +echo +echo "=== detect-zeroes=on - write actual zeros ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,detect-zeroes=on \ + | filter_command +print_disk_usage + +echo +echo "=== detect-zeroes=on,discard=on - write actual zeros ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,detect-zeroes=on,discard=on \ + | filter_command +print_disk_usage + +echo +echo "=== discard=on - write zeroes ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -z 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=on \ + | filter_command +print_disk_usage + +echo +echo "=== discard=on - write zeroes unmap ===" +echo + +create_test_image +echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \ + | $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=on \ + | filter_command +print_disk_usage diff --git a/tests/qemu-iotests/tests/write-zeroes-unmap.out b/tests/qemu-iotests/tests/write-zeroes-unmap.out new file mode 100644 index 0000000000..c931994897 --- /dev/null +++ b/tests/qemu-iotests/tests/write-zeroes-unmap.out @@ -0,0 +1,81 @@ +QA output created by write-zeroes-unmap + +=== defaults - write zeros === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -z 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== defaults - write zeros unmap === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -zu 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== defaults - write actual zeros === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -P 0 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== discard=off - write zeroes unmap === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -zu 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== detect-zeroes=on - write actual zeros === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -P 0 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== detect-zeroes=on,discard=on - write actual zeros === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -P 0 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== discard=on - write zeroes === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -z 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +1.0M TEST_DIR/t.raw + +=== discard=on - write zeroes unmap === + +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576 +QEMU X.Y.Z monitor - type 'help' for more information +(qemu) qemu-io none0 "write -zu 0 1m" +wrote 1048576/1048576 bytes at offset 0 +1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +(qemu) quit +0 TEST_DIR/t.raw -- 2.45.2
