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qcow2: Forbid discard in qcow2 v2 images with backing files
A discard request deallocates the selected clusters so they read back as zeroes. This is done by clearing the cluster offset field and setting QCOW_OFLAG_ZERO in the L2 entry. This flag is however only supported when qcow_version >= 3. In older images the cluster is simply deallocated, exposing any possible stale data from the backing file. Since discard is an advisory operation it's safer to simply forbid it in this scenario. Note that we are adding this check to qcow2_co_pdiscard() and not to qcow2_cluster_discard() or discard_in_l2_slice() because the last two are also used by qcow2_snapshot_create() to discard the clusters used by the VM state. In this case there's no risk of exposing stale data to the guest and we really want that the clusters are always discarded. Signed-off-by: Alberto Garcia <berto@igalia.com> Message-Id: <20200331114345.29993-1-berto@igalia.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Alberto Garcia
Max Reitz
parent
53ef8a92eb
commit
80f5c01183
@ -3784,6 +3784,12 @@ static coroutine_fn int qcow2_co_pdiscard(BlockDriverState *bs,
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int ret;
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BDRVQcow2State *s = bs->opaque;
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/* If the image does not support QCOW_OFLAG_ZERO then discarding
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* clusters could expose stale data from the backing file. */
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if (s->qcow_version < 3 && bs->backing) {
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return -ENOTSUP;
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}
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if (!QEMU_IS_ALIGNED(offset | bytes, s->cluster_size)) {
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assert(bytes < s->cluster_size);
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/* Ignore partial clusters, except for the special case of the
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@ -193,8 +193,8 @@ echo "== Verify image content =="
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verify_io()
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{
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if ($QEMU_IMG info -U -f "$IMGFMT" "$TEST_IMG" | grep "compat: 0.10" > /dev/null); then
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# For v2 images, discarded clusters are read from the backing file
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# Keep the variable empty so that the backing file value can be used as
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# In v2 images clusters are not discarded when there is a backing file.
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# Keep the variable empty so that the previous value can be used as
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# the default below
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discarded=
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else
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@ -230,14 +230,16 @@ verify_io()
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echo read -P 70 0x78000 0x6000
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echo read -P 7 0x7e000 0x2000
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echo read -P ${discarded:-8} 0x80000 0x6000
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echo read -P ${discarded:-89} 0x80000 0x1000
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echo read -P ${discarded:-8} 0x81000 0x5000
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echo read -P 80 0x86000 0x2000
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echo read -P ${discarded:-8} 0x88000 0x2000
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echo read -P 81 0x8a000 0xe000
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echo read -P 90 0x98000 0x6000
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echo read -P 9 0x9e000 0x2000
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echo read -P ${discarded:-10} 0xa0000 0x6000
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echo read -P ${discarded:-109} 0xa0000 0x1000
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echo read -P ${discarded:-10} 0xa1000 0x5000
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echo read -P 100 0xa6000 0x2000
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echo read -P ${discarded:-10} 0xa8000 0x2000
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echo read -P 101 0xaa000 0xe000
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@ -187,8 +187,10 @@ read 24576/24576 bytes at offset 491520
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24 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 516096
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8 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 24576/24576 bytes at offset 524288
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24 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 4096/4096 bytes at offset 524288
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4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 20480/20480 bytes at offset 528384
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20 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 548864
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8 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 557056
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@ -199,8 +201,10 @@ read 24576/24576 bytes at offset 622592
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24 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 647168
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8 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 24576/24576 bytes at offset 655360
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24 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 4096/4096 bytes at offset 655360
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4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 20480/20480 bytes at offset 659456
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20 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 679936
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8 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 8192/8192 bytes at offset 688128
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@ -160,18 +160,16 @@ TEST_IMG=$BACKING_IMG _make_test_img 1G
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$QEMU_IO -c 'write 0k 64k' "$BACKING_IMG" | _filter_qemu_io
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# compat=0.10 is required in order to make the following discard actually
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# unallocate the sector rather than make it a zero sector - we want COW, after
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# all.
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_make_test_img -o 'compat=0.10' -b "$BACKING_IMG" 1G
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_make_test_img -b "$BACKING_IMG" 1G
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# Write two clusters, the second one enforces creation of an L2 table after
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# the first data cluster.
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$QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io
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# Discard the first cluster. This cluster will soon enough be reallocated and
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# Free the first cluster. This cluster will soon enough be reallocated and
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# used for COW.
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$QEMU_IO -c 'discard 0k 64k' "$TEST_IMG" | _filter_qemu_io
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poke_file "$TEST_IMG" "$l2_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"
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poke_file "$TEST_IMG" "$(($rb_offset+10))" "\x00\x00"
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# Now, corrupt the image by marking the second L2 table cluster as free.
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poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c
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poke_file "$TEST_IMG" "$(($rb_offset+12))" "\x00\x00"
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# Start a write operation requiring COW on the image stopping it right before
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# doing the read; then, trigger the corruption prevention by writing anything to
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# any unallocated cluster, leading to an attempt to overwrite the second L2
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@ -105,8 +105,6 @@ wrote 65536/65536 bytes at offset 0
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64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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wrote 65536/65536 bytes at offset 536870912
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64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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discard 65536/65536 bytes at offset 0
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64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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qcow2: Marking image as corrupt: Preventing invalid write on metadata (overlaps with active L2 table); further corruption events will be suppressed
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blkdebug: Suspended request '0'
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write failed: Input/output error
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@ -89,8 +89,9 @@ verify_io()
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{
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if ($QEMU_IMG info -f "$IMGFMT" "$TEST_IMG" |
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grep "compat: 0.10" > /dev/null); then
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# For v2 images, discarded clusters are read from the backing file
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discarded=11
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# In v2 images clusters are not discarded when there is a backing file
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# so the previous value is read
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discarded=22
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else
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# Discarded clusters are zeroed for v3 or later
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discarded=0
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97
tests/qemu-iotests/290
Executable file
97
tests/qemu-iotests/290
Executable file
@ -0,0 +1,97 @@
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#!/usr/bin/env bash
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#
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# Test how 'qemu-io -c discard' behaves on v2 and v3 qcow2 images
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#
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# Copyright (C) 2020 Igalia, S.L.
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# Author: Alberto Garcia <berto@igalia.com>
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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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# creator
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owner=berto@igalia.com
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seq=`basename $0`
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echo "QA output created by $seq"
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status=1 # failure is the default!
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_cleanup()
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{
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_cleanup_test_img
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}
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trap "_cleanup; exit \$status" 0 1 2 3 15
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# get standard environment, filters and checks
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. ./common.rc
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. ./common.filter
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_supported_fmt qcow2
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_supported_proto file
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_supported_os Linux
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_unsupported_imgopts 'compat=0.10' refcount_bits data_file
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echo
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echo "### Test 'qemu-io -c discard' on a QCOW2 image without a backing file"
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echo
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for qcow2_compat in 0.10 1.1; do
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echo "# Create an image with compat=$qcow2_compat without a backing file"
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_make_test_img -o "compat=$qcow2_compat" 128k
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echo "# Fill all clusters with data and then discard them"
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$QEMU_IO -c 'write -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io
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$QEMU_IO -c 'discard 0 128k' "$TEST_IMG" | _filter_qemu_io
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echo "# Read the data from the discarded clusters"
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$QEMU_IO -c 'read -P 0x00 0 128k' "$TEST_IMG" | _filter_qemu_io
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echo "# Output of qemu-img map"
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$QEMU_IMG map "$TEST_IMG" | _filter_testdir
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done
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echo
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echo "### Test 'qemu-io -c discard' on a QCOW2 image with a backing file"
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echo
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echo "# Create a backing image and fill it with data"
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BACKING_IMG="$TEST_IMG.base"
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TEST_IMG="$BACKING_IMG" _make_test_img 128k
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$QEMU_IO -c 'write -P 0xff 0 128k' "$BACKING_IMG" | _filter_qemu_io
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for qcow2_compat in 0.10 1.1; do
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echo "# Create an image with compat=$qcow2_compat and a backing file"
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_make_test_img -o "compat=$qcow2_compat" -b "$BACKING_IMG"
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echo "# Fill all clusters with data and then discard them"
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$QEMU_IO -c 'write -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io
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$QEMU_IO -c 'discard 0 128k' "$TEST_IMG" | _filter_qemu_io
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echo "# Read the data from the discarded clusters"
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if [ "$qcow2_compat" = "1.1" ]; then
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# In qcow2 v3 clusters are zeroed (with QCOW_OFLAG_ZERO)
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$QEMU_IO -c 'read -P 0x00 0 128k' "$TEST_IMG" | _filter_qemu_io
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else
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# In qcow2 v2 if there's a backing image we cannot zero the clusters
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# without exposing the backing file data so discard does nothing
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$QEMU_IO -c 'read -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io
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fi
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echo "# Output of qemu-img map"
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$QEMU_IMG map "$TEST_IMG" | _filter_testdir
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done
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# success, all done
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echo "*** done"
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rm -f $seq.full
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status=0
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61
tests/qemu-iotests/290.out
Normal file
61
tests/qemu-iotests/290.out
Normal file
@ -0,0 +1,61 @@
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QA output created by 290
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### Test 'qemu-io -c discard' on a QCOW2 image without a backing file
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# Create an image with compat=0.10 without a backing file
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072
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# Fill all clusters with data and then discard them
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wrote 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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discard 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Read the data from the discarded clusters
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read 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Output of qemu-img map
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Offset Length Mapped to File
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# Create an image with compat=1.1 without a backing file
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072
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# Fill all clusters with data and then discard them
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wrote 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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discard 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Read the data from the discarded clusters
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read 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Output of qemu-img map
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Offset Length Mapped to File
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### Test 'qemu-io -c discard' on a QCOW2 image with a backing file
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# Create a backing image and fill it with data
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Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=131072
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wrote 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Create an image with compat=0.10 and a backing file
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base
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# Fill all clusters with data and then discard them
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wrote 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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discard 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Read the data from the discarded clusters
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read 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Output of qemu-img map
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Offset Length Mapped to File
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0 0x20000 0x50000 TEST_DIR/t.qcow2
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# Create an image with compat=1.1 and a backing file
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=131072 backing_file=TEST_DIR/t.IMGFMT.base
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# Fill all clusters with data and then discard them
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wrote 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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discard 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Read the data from the discarded clusters
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read 131072/131072 bytes at offset 0
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128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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# Output of qemu-img map
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Offset Length Mapped to File
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*** done
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@ -296,3 +296,4 @@
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286 rw quick
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288 quick
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289 rw quick
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290 rw auto quick
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