Re: [Qemu-devel] [PATCH] block: Fix bdrv_commit return value

[Jeff Cody]

On Fri, Jan 24, 2014 at 02:08:21PM +0100, Kevin Wolf wrote:
> bdrv_commit() could return 0 or 1 on success, depending on whether or
> now the last sector was allocated in the overlay and whether the overlay
> format had a .bdrv_make_empty callback.
> 
> Most callers ignored it, but qemu-img commit would print an error
> message while the operation actually succeeded.
> 
> Also clean up the handling of I/O errors to return the real error code
> instead of -EIO.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 3e0994b..7d22ca9 100644
> --- a/block.c
> +++ b/block.c
> @@ -2061,13 +2061,13 @@ int bdrv_commit(BlockDriverState *bs)
>              goto ro_cleanup;
>          }
>          if (ret) {
> -            if (bdrv_read(bs, sector, buf, n) != 0) {
> -                ret = -EIO;
> +            ret = bdrv_read(bs, sector, buf, n);
> +            if (ret < 0) {
>                  goto ro_cleanup;
>              }
>  
> -            if (bdrv_write(bs->backing_hd, sector, buf, n) != 0) {
> -                ret = -EIO;
> +            ret = bdrv_write(bs->backing_hd, sector, buf, n);
> +            if (ret < 0) {
>                  goto ro_cleanup;
>              }
>          }
> @@ -2075,6 +2075,9 @@ int bdrv_commit(BlockDriverState *bs)
>  
>      if (drv->bdrv_make_empty) {
>          ret = drv->bdrv_make_empty(bs);
> +        if (ret < 0) {
> +            goto ro_cleanup;
> +        }

QED has a .bdrv_make_empty implementation, but it is a stub that
always returns -ENOTSUP.

Prior to this patch, a commit of a QED snapshot would complete OK, but
return an error saying "Image is already committed" (Which almost
seems like a non-error error).

Now, we'll skip ahead to cleanup.

I think we should either: 1) filter out -ENOTSUP here, or 2) remove
the stub from QED

>          bdrv_flush(bs);
>      }
>  
> @@ -2082,9 +2085,11 @@ int bdrv_commit(BlockDriverState *bs)
>       * Make sure all data we wrote to the backing device is actually
>       * stable on disk.
>       */
> -    if (bs->backing_hd)
> +    if (bs->backing_hd) {
>          bdrv_flush(bs->backing_hd);
> +    }
>  
> +    ret = 0;
>  ro_cleanup:
>      g_free(buf);
>  
> -- 
> 1.8.1.4
>