Re: [PATCH] qcow2: Use a GString in report_unsupported_feature()

[Alex Bennée]

Alberto Garcia <address@hidden> writes:

> This is a bit more efficient than having to allocate and free memory
> for each item.
>
> The default size (60) is enough for all the existing incompatible
> features.
>
> Suggested-by: Philippe Mathieu-Daudé <address@hidden>
> Signed-off-by: Alberto Garcia <address@hidden>
> ---
>  block/qcow2.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index cef9d72b3a..ecf6827420 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -453,16 +453,15 @@ static void cleanup_unknown_header_ext(BlockDriverState 
> *bs)
>  static void report_unsupported_feature(Error **errp, Qcow2Feature *table,
>                                         uint64_t mask)
>  {
> -    char *features = g_strdup("");
> -    char *old;
> +    GString *features = g_string_sized_new(60);

       g_autoptr(GString) features = g_string_sized_new(60);

will save you the clean-up later.

>  
>      while (table && table->name[0] != '\0') {
>          if (table->type == QCOW2_FEAT_TYPE_INCOMPATIBLE) {
>              if (mask & (1ULL << table->bit)) {
> -                old = features;
> -                features = g_strdup_printf("%s%s%.46s", old, *old ? ", " : 
> "",
> -                                           table->name);
> -                g_free(old);
> +                if (features->len > 0) {
> +                    g_string_append(features, ", ");
> +                }
> +                g_string_append_printf(features, "%.46s",
>      table->name);

We have a number of cases of this sort of idiom in the code base. I
wonder if it calls for a utility function:

       qemu_append_with_sep(features, ", ", "%.46s", table->name)

Anyway not mandatory for this patch so with the autoptr fix:

Reviewed-by: Alex Bennée <address@hidden>

>                  mask &= ~(1ULL << table->bit);
>              }
>          }
> @@ -470,14 +469,15 @@ static void report_unsupported_feature(Error **errp, 
> Qcow2Feature *table,
>      }
>  
>      if (mask) {
> -        old = features;
> -        features = g_strdup_printf("%s%sUnknown incompatible feature: %" 
> PRIx64,
> -                                   old, *old ? ", " : "", mask);
> -        g_free(old);
> +        if (features->len > 0) {
> +            g_string_append(features, ", ");
> +        }
> +        g_string_append_printf(features,
> +                               "Unknown incompatible feature: %" PRIx64, 
> mask);
>      }
>  
> -    error_setg(errp, "Unsupported qcow2 feature(s): %s", features);
> -    g_free(features);
> +    error_setg(errp, "Unsupported qcow2 feature(s): %s", features->str);
> +    g_string_free(features, TRUE);
>  }
>  
>  /*


-- 
Alex Bennée