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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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26
qemu-img.c
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@ -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");