Consider discard option when writing zeros
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 <nsoffer@redhat.com> Message-id: 20240628202058.1964986-3-nsoffer@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Nir Soffer
Stefan Hajnoczi
parent
249d0f8397
commit
d05ae948cc
@ -1862,6 +1862,11 @@ bdrv_co_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
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return -EINVAL;
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}
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/* If opened with discard=off we should never unmap. */
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if (!(bs->open_flags & BDRV_O_UNMAP)) {
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flags &= ~BDRV_REQ_MAY_UNMAP;
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}
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/* Invalidate the cached block-status data range if this write overlaps */
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bdrv_bsc_invalidate_range(bs, offset, bytes);
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@ -2315,10 +2320,6 @@ int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild *child, int64_t offset,
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trace_bdrv_co_pwrite_zeroes(child->bs, offset, bytes, flags);
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assert_bdrv_graph_readable();
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if (!(child->bs->open_flags & BDRV_O_UNMAP)) {
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flags &= ~BDRV_REQ_MAY_UNMAP;
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}
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return bdrv_co_pwritev(child, offset, bytes, NULL,
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BDRV_REQ_ZERO_WRITE | flags);
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}
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127
tests/qemu-iotests/tests/write-zeroes-unmap
Executable file
127
tests/qemu-iotests/tests/write-zeroes-unmap
Executable file
@ -0,0 +1,127 @@
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#!/usr/bin/env bash
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# group: quick
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#
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# Test write zeros unmap.
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#
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# Copyright (C) Red Hat, Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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seq="$(basename $0)"
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echo "QA output created by $seq"
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trap _cleanup_test_img exit
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# get standard environment, filters and checks
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cd ..
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. ./common.rc
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. ./common.filter
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_supported_fmt raw
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_supported_proto file
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_supported_os Linux
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create_test_image() {
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_make_test_img -f $IMGFMT 1m
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}
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filter_command() {
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_filter_testdir | _filter_qemu_io | _filter_qemu | _filter_hmp
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}
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print_disk_usage() {
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du -sh $TEST_IMG | _filter_testdir
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}
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echo
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echo "=== defaults - write zeros ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -z 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \
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| filter_command
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print_disk_usage
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echo
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echo "=== defaults - write zeros unmap ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \
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| filter_command
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print_disk_usage
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echo
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echo "=== defaults - write actual zeros ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT \
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| filter_command
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print_disk_usage
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echo
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echo "=== discard=off - write zeroes unmap ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=off \
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| filter_command
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print_disk_usage
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echo
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echo "=== detect-zeroes=on - write actual zeros ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,detect-zeroes=on \
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| filter_command
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print_disk_usage
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echo
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echo "=== detect-zeroes=on,discard=on - write actual zeros ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -P 0 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,detect-zeroes=on,discard=on \
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| filter_command
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print_disk_usage
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echo
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echo "=== discard=on - write zeroes ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -z 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=on \
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| filter_command
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print_disk_usage
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echo
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echo "=== discard=on - write zeroes unmap ==="
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echo
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create_test_image
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echo -e 'qemu-io none0 "write -zu 0 1m"\nquit' \
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| $QEMU -monitor stdio -drive if=none,file=$TEST_IMG,format=$IMGFMT,discard=on \
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| filter_command
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print_disk_usage
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81
tests/qemu-iotests/tests/write-zeroes-unmap.out
Normal file
81
tests/qemu-iotests/tests/write-zeroes-unmap.out
Normal file
@ -0,0 +1,81 @@
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QA output created by write-zeroes-unmap
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=== defaults - write zeros ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -z 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== defaults - write zeros unmap ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -zu 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== defaults - write actual zeros ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -P 0 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== discard=off - write zeroes unmap ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -zu 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== detect-zeroes=on - write actual zeros ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -P 0 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== detect-zeroes=on,discard=on - write actual zeros ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -P 0 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== discard=on - write zeroes ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -z 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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1.0M TEST_DIR/t.raw
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=== discard=on - write zeroes unmap ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
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QEMU X.Y.Z monitor - type 'help' for more information
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(qemu) qemu-io none0 "write -zu 0 1m"
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wrote 1048576/1048576 bytes at offset 0
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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(qemu) quit
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0 TEST_DIR/t.raw
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