Re: [PATCH v6 4/5] qemu-img: Add convert --bitmaps option

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

21.05.2020 22:21, Eric Blake wrote:
> Make it easier to copy all the persistent bitmaps of (the top layer
> of) a source image along with its guest-visible contents, by adding a
> boolean flag for use with qemu-img convert.  This is basically
> shorthand, as the same effect could be accomplished with a series of
> 'qemu-img bitmap --add' and 'qemu-img bitmap --merge -b source'
> commands, or by their corresponding QMP commands.
> 
> Note that this command will fail in the same scenarios where 'qemu-img
> measure' omits a 'bitmaps size:' line, namely, when either the source
> or the destination lacks persistent bitmap support altogether.
> 
> See also https://bugzilla.redhat.com/show_bug.cgi?id=1779893
> 
> While touching this, clean up a couple coding issues spotted in the
> same function: an extra blank line, and merging back-to-back 'if
> (!skip_create)' blocks.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---

[..]

> diff --git a/qemu-img.c b/qemu-img.c
> index 0778d8f56614..8ecebe178890 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -78,6 +78,7 @@ enum {
>       OPTION_ENABLE = 272,
>       OPTION_DISABLE = 273,
>       OPTION_MERGE = 274,

[..]

> 
>   static int img_convert(int argc, char **argv)
> @@ -2160,6 +2195,8 @@ static int img_convert(int argc, char **argv)
>       int64_t ret = -EINVAL;
>       bool force_share = false;
>       bool explict_min_sparse = false;
> +    bool bitmaps = false;
> +    size_t nbitmaps = 0;
> 
>       ImgConvertState s = (ImgConvertState) {
>           /* Need at least 4k of zeros for sparse detection */
> @@ -2179,6 +2216,7 @@ static int img_convert(int argc, char **argv)
>               {"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},
> +            {"bitmaps", no_argument, 0, OPTION_BITMAPS},
>               {0, 0, 0, 0}
>           };
>           c = getopt_long(argc, argv, ":hf:O:B:Cco:l:S:pt:T:qnm:WU",
> @@ -2304,6 +2342,9 @@ static int img_convert(int argc, char **argv)
>                */
>               s.has_zero_init = true;
>               break;
> +        case OPTION_BITMAPS:
> +            bitmaps = true;
> +            break;
>           }
>       }
> 
> @@ -2365,7 +2406,6 @@ static int img_convert(int argc, char **argv)
>           goto fail_getopt;
>       }
> 
> -
>       /* ret is still -EINVAL until here */
>       ret = bdrv_parse_cache_mode(src_cache, &src_flags, &src_writethrough);
>       if (ret < 0) {
> @@ -2525,6 +2565,27 @@ static int img_convert(int argc, char **argv)
>           }
>       }
> 
> +    /* Determine how many bitmaps need copying */
> +    if (bitmaps) {
> +        BdrvDirtyBitmap *bm;
> +
> +        if (s.src_num > 1) {
> +            error_report("Copying bitmaps only possible with single source");
> +            ret = -1;
> +            goto out;
> +        }
> +        if (!bdrv_supports_persistent_dirty_bitmap(blk_bs(s.src[0]))) {
> +            error_report("Source lacks bitmap support");
> +            ret = -1;
> +            goto out;
> +        }
> +        FOR_EACH_DIRTY_BITMAP(blk_bs(s.src[0]), bm) {
> +            if (bdrv_dirty_bitmap_get_persistence(bm)) {
> +                nbitmaps++;
> +            }
> +        }
> +    }
> +
>       /*
>        * The later open call will need any decryption secrets, and
>        * bdrv_create() will purge "opts", so extract them now before
> @@ -2533,9 +2594,7 @@ static int img_convert(int argc, char **argv)
>       if (!skip_create) {
>           open_opts = qdict_new();
>           qemu_opt_foreach(opts, img_add_key_secrets, open_opts, &error_abort);
> -    }
> 
> -    if (!skip_create) {
>           /* Create the new image */
>           ret = bdrv_create(drv, out_filename, opts, &local_err);
>           if (ret < 0) {
> @@ -2573,6 +2632,13 @@ static int img_convert(int argc, char **argv)
>       }
>       out_bs = blk_bs(s.target);
> 
> +    if (nbitmaps > 0 && !bdrv_supports_persistent_dirty_bitmap(out_bs)) {

We will not fail, if target doesn't support bitmaps, source supports them but has no bitmaps? Doesn't seem to be a problem, but a bit less strict than you write in commit message.

So, maybe, s/nbitmaps > 0/bitmaps/

> +        error_report("Format driver '%s' does not support bitmaps",
> +                     out_fmt);

Hmm seems, out_fmt may be NULL at this point, consider the path:
const char *out_fmt = NULL
...
[no -O option]
--target-image-opts, so out_fmt doesn't default to "raw" but remains NULL
...

So, with s/out_fmt/out_bs->drv->format_name/ (and with or without s/nbitmaps > 0/bitmaps/):


Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>


-- 
Best regards,
Vladimir