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qemu-img: Add --target-is-zero to convert

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In many cases the target of a convert operation is a newly provisioned
target that the user knows is blank (reads as zero). In this situation
there is no requirement for qemu-img to wastefully zero out the entire
device.

Add a new option, --target-is-zero, allowing the user to indicate that
an existing target device will return zeros for all reads.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20200205110248.2009589-2-david.edmondson@oracle.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
David Edmondson 2020-02-05 11:02:48 +00:00 committed by Max Reitz
parent facda5443f
commit 168468fe19
3 changed files with 33 additions and 6 deletions
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9
docs/interop/qemu-img.rst
View File

@ -214,6 +214,13 @@ Parameters to convert subcommand:
will still be printed. Areas that cannot be read from the source will be
treated as containing only zeroes.
.. option:: --target-is-zero
Assume that reading the destination image will always return
zeros. This parameter is mutually exclusive with a destination image
that has a backing file. It is required to also use the ``-n``
parameter to skip image creation.
Parameters to dd subcommand:
.. program:: qemu-img-dd
@ -366,7 +373,7 @@ Command description:
4
Error on reading data
.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
Convert the disk image *FILENAME* or a snapshot *SNAPSHOT_PARAM*
to disk image *OUTPUT_FILENAME* using format *OUTPUT_FMT*. It can

4
qemu-img-cmds.hx
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@ -39,9 +39,9 @@ SRST
ERST
DEF("convert", img_convert,
"convert [--object objectdef] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-B backing_file] [-o options] [-l snapshot_param] [-S sparse_size] [-m num_coroutines] [-W] [--salvage] filename [filename2 [...]] output_filename")
"convert [--object objectdef] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-B backing_file] [-o options] [-l snapshot_param] [-S sparse_size] [-m num_coroutines] [-W] [--salvage] filename [filename2 [...]] output_filename")
SRST
.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] [--salvage] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] [--salvage] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
ERST
DEF("create", img_create,

26
qemu-img.c
View File

@ -70,6 +70,7 @@ enum {
OPTION_PREALLOCATION = 265,
OPTION_SHRINK = 266,
OPTION_SALVAGE = 267,
OPTION_TARGET_IS_ZERO = 268,
};
typedef enum OutputFormat {
@ -1984,10 +1985,9 @@ static int convert_do_copy(ImgConvertState *s)
int64_t sector_num = 0;
/* Check whether we have zero initialisation or can get it efficiently */
if (s->target_is_new && s->min_sparse && !s->target_has_backing) {
if (!s->has_zero_init && s->target_is_new && s->min_sparse &&
!s->target_has_backing) {
s->has_zero_init = bdrv_has_zero_init(blk_bs(s->target));
} else {
s->has_zero_init = false;
}
if (!s->has_zero_init && !s->target_has_backing &&
@ -2086,6 +2086,7 @@ static int img_convert(int argc, char **argv)
{"force-share", no_argument, 0, 'U'},
{"target-image-opts", no_argument, 0, OPTION_TARGET_IMAGE_OPTS},
{"salvage", no_argument, 0, OPTION_SALVAGE},
{"target-is-zero", no_argument, 0, OPTION_TARGET_IS_ZERO},
{0, 0, 0, 0}
};
c = getopt_long(argc, argv, ":hf:O:B:Cco:l:S:pt:T:qnm:WU",
@ -2209,6 +2210,14 @@ static int img_convert(int argc, char **argv)
case OPTION_TARGET_IMAGE_OPTS:
tgt_image_opts = true;
break;
case OPTION_TARGET_IS_ZERO:
/*
* The user asserting that the target is blank has the
* same effect as the target driver supporting zero
* initialisation.
*/
s.has_zero_init = true;
break;
}
}
@ -2247,6 +2256,11 @@ static int img_convert(int argc, char **argv)
warn_report("This will become an error in future QEMU versions.");
}
if (s.has_zero_init && !skip_create) {
error_report("--target-is-zero requires use of -n flag");
goto fail_getopt;
}
s.src_num = argc - optind - 1;
out_filename = s.src_num >= 1 ? argv[argc - 1] : NULL;
@ -2380,6 +2394,12 @@ static int img_convert(int argc, char **argv)
}
s.target_has_backing = (bool) out_baseimg;
if (s.has_zero_init && s.target_has_backing) {
error_report("Cannot use --target-is-zero when the destination "
"image has a backing file");
goto out;
}
if (s.src_num > 1 && out_baseimg) {
error_report("Having a backing file for the target makes no sense when "
"concatenating multiple input images");