jcs.org
qemu with hax to log dma reads & writes
jcs.org/2018/11/12/vfio
qemu-img: add --shrink flag for resize
The flag is additional precaution against data loss. Perhaps in the future the
operation shrink without this flag will be blocked for all formats, but for now
we need to maintain compatibility with raw.
Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20170918124230.8152-2-pbutsykin@virtuozzo.com
[mreitz: Added a missing space to a warning]
Signed-off-by: Max Reitz <mreitz@redhat.com>
authored by
Pavel Butsykin
and committed by
Max Reitz
4ffca890
69ff158b
+33
-6
+2
-2
qemu-img-cmds.hx
+2
-2
qemu-img-cmds.hx
···
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ETEXI
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DEF("resize", img_resize,
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-
"resize [--object objectdef] [--image-opts] [-q] filename [+ | -]size")
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+
"resize [--object objectdef] [--image-opts] [-q] [--shrink] filename [+ | -]size")
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STEXI
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-
@item resize [--object @var{objectdef}] [--image-opts] [-q] @var{filename} [+ | -]@var{size}
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+
@item resize [--object @var{objectdef}] [--image-opts] [-q] [--shrink] @var{filename} [+ | -]@var{size}
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ETEXI
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STEXI
+23
qemu-img.c
+23
qemu-img.c
···
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OPTION_TARGET_IMAGE_OPTS = 263,
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OPTION_SIZE = 264,
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OPTION_PREALLOCATION = 265,
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OPTION_SHRINK = 266,
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};
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typedef enum OutputFormat {
···
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},
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};
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bool image_opts = false;
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+
bool shrink = false;
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/* Remove size from argv manually so that negative numbers are not treated
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* as options by getopt. */
···
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{"object", required_argument, 0, OPTION_OBJECT},
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{"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
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{"preallocation", required_argument, 0, OPTION_PREALLOCATION},
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+
{"shrink", no_argument, 0, OPTION_SHRINK},
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{0, 0, 0, 0}
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};
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c = getopt_long(argc, argv, ":f:hq",
···
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error_report("Invalid preallocation mode '%s'", optarg);
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return 1;
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}
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break;
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case OPTION_SHRINK:
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shrink = true;
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break;
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}
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}
···
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error_report("Preallocation can only be used for growing images");
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ret = -1;
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goto out;
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+
}
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+
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+
if (total_size < current_size && !shrink) {
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+
warn_report("Shrinking an image will delete all data beyond the "
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+
"shrunken image's end. Before performing such an "
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+
"operation, make sure there is no important data there.");
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+
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+
if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
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error_report(
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"Use the --shrink option to perform a shrink operation.");
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ret = -1;
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+
goto out;
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+
} else {
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warn_report("Using the --shrink option will suppress this message. "
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+
"Note that future versions of qemu-img may refuse to "
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+
"shrink images without this option.");
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+
}
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}
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ret = blk_truncate(blk, total_size, prealloc, &err);
+5
-1
qemu-img.texi
+5
-1
qemu-img.texi
···
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At this point, @code{modified.img} can be discarded, since
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@code{base.img + diff.qcow2} contains the same information.
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-
@item resize [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size}
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+
@item resize [--shrink] [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size}
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Change the disk image as if it had been created with @var{size}.
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Before using this command to shrink a disk image, you MUST use file system and
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partitioning tools inside the VM to reduce allocated file systems and partition
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sizes accordingly. Failure to do so will result in data loss!
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+
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+
When shrinking images, the @code{--shrink} option must be given. This informs
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+
qemu-img that the user acknowledges all loss of data beyond the truncated
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+
image's end.
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After using this command to grow a disk image, you must use file system and
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partitioning tools inside the VM to actually begin using the new space on the
+2
-2
tests/qemu-iotests/102
+2
-2
tests/qemu-iotests/102
···
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$QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
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# Remove data cluster from image (first cluster: image header, second: reftable,
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# third: refblock, fourth: L1 table, fifth: L2 table)
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-
$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
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+
$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
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$QEMU_IO -c map "$TEST_IMG"
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$QEMU_IMG map "$TEST_IMG"
···
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qemu_comm_method=monitor _launch_qemu -drive if=none,file="$TEST_IMG",id=drv0
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-
$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
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+
$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
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_send_qemu_cmd $QEMU_HANDLE 'qemu-io drv0 map' 'allocated' \
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| sed -e 's/^(qemu).*qemu-io drv0 map...$/(qemu) qemu-io drv0 map/'
+1
-1
tests/qemu-iotests/106
+1
-1
tests/qemu-iotests/106
···
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for growth_mode in falloc full off; do
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echo
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echo "--- growth_mode=$growth_mode ---"
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-
$QEMU_IMG resize -f "$IMGFMT" --preallocation=$growth_mode "$TEST_IMG" -${GROWTH_SIZE}K
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+
$QEMU_IMG resize -f "$IMGFMT" --shrink --preallocation=$growth_mode "$TEST_IMG" -${GROWTH_SIZE}K
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done
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# success, all done