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qemu-img: add --shrink flag for resize

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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>
This commit is contained in:
Pavel Butsykin 2017-09-18 15:42:27 +03:00 committed by Max Reitz
parent 69ff158b67
commit 4ffca8904a
5 changed files with 33 additions and 6 deletions
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4
qemu-img-cmds.hx
View File

@ -89,9 +89,9 @@ STEXI
ETEXI
DEF("resize", img_resize,
"resize [--object objectdef] [--image-opts] [-q] filename [+ | -]size")
"resize [--object objectdef] [--image-opts] [-q] [--shrink] filename [+ | -]size")
STEXI
@item resize [--object @var{objectdef}] [--image-opts] [-q] @var{filename} [+ | -]@var{size}
@item resize [--object @var{objectdef}] [--image-opts] [-q] [--shrink] @var{filename} [+ | -]@var{size}
ETEXI
STEXI

23
qemu-img.c
View File

@ -64,6 +64,7 @@ enum {
OPTION_TARGET_IMAGE_OPTS = 263,
OPTION_SIZE = 264,
OPTION_PREALLOCATION = 265,
OPTION_SHRINK = 266,
};
typedef enum OutputFormat {
@ -3436,6 +3437,7 @@ static int img_resize(int argc, char **argv)
},
};
bool image_opts = false;
bool shrink = false;
/* Remove size from argv manually so that negative numbers are not treated
* as options by getopt. */
@ -3454,6 +3456,7 @@ static int img_resize(int argc, char **argv)
{"object", required_argument, 0, OPTION_OBJECT},
{"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
{"preallocation", required_argument, 0, OPTION_PREALLOCATION},
{"shrink", no_argument, 0, OPTION_SHRINK},
{0, 0, 0, 0}
};
c = getopt_long(argc, argv, ":f:hq",
@ -3496,6 +3499,9 @@ static int img_resize(int argc, char **argv)
return 1;
}
break;
case OPTION_SHRINK:
shrink = true;
break;
}
}
if (optind != argc - 1) {
@ -3569,6 +3575,23 @@ static int img_resize(int argc, char **argv)
goto out;
}
if (total_size < current_size && !shrink) {
warn_report("Shrinking an image will delete all data beyond the "
"shrunken image's end. Before performing such an "
"operation, make sure there is no important data there.");
if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
error_report(
"Use the --shrink option to perform a shrink operation.");
ret = -1;
goto out;
} else {
warn_report("Using the --shrink option will suppress this message. "
"Note that future versions of qemu-img may refuse to "
"shrink images without this option.");
}
}
ret = blk_truncate(blk, total_size, prealloc, &err);
if (!ret) {
qprintf(quiet, "Image resized.\n");

6
qemu-img.texi
View File

@ -545,7 +545,7 @@ qemu-img rebase -b base.img diff.qcow2
At this point, @code{modified.img} can be discarded, since
@code{base.img + diff.qcow2} contains the same information.
@item resize [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size}
@item resize [--shrink] [--preallocation=@var{prealloc}] @var{filename} [+ | -]@var{size}
Change the disk image as if it had been created with @var{size}.
@ -553,6 +553,10 @@ Before using this command to shrink a disk image, you MUST use file system and
partitioning tools inside the VM to reduce allocated file systems and partition
sizes accordingly. Failure to do so will result in data loss!
When shrinking images, the @code{--shrink} option must be given. This informs
qemu-img that the user acknowledges all loss of data beyond the truncated
image's end.
After using this command to grow a disk image, you must use file system and
partitioning tools inside the VM to actually begin using the new space on the
device.

4
tests/qemu-iotests/102
View File

@ -54,7 +54,7 @@ _make_test_img $IMG_SIZE
$QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
# Remove data cluster from image (first cluster: image header, second: reftable,
# third: refblock, fourth: L1 table, fifth: L2 table)
$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
$QEMU_IO -c map "$TEST_IMG"
$QEMU_IMG map "$TEST_IMG"
@ -69,7 +69,7 @@ $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
qemu_comm_method=monitor _launch_qemu -drive if=none,file="$TEST_IMG",id=drv0
$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
_send_qemu_cmd $QEMU_HANDLE 'qemu-io drv0 map' 'allocated' \
| sed -e 's/^(qemu).*qemu-io drv0 map...$/(qemu) qemu-io drv0 map/'

2
tests/qemu-iotests/106
View File

@ -83,7 +83,7 @@ echo '=== Testing image shrinking ==='
for growth_mode in falloc full off; do
echo
echo "--- growth_mode=$growth_mode ---"
$QEMU_IMG resize -f "$IMGFMT" --preallocation=$growth_mode "$TEST_IMG" -${GROWTH_SIZE}K
$QEMU_IMG resize -f "$IMGFMT" --shrink --preallocation=$growth_mode "$TEST_IMG" -${GROWTH_SIZE}K
done
# success, all done