Re: [Qemu-devel] [PATCH] qemu-img: fix error messages emitted by img_open()

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Jul 21, 2016 at 10:41:53AM +0200, Reda Sallahi wrote:
> img_open_file() and img_open_opts() were printing error messages with a
> duplicate part because of a wrong use of error_reportf_err() (e.g.
> qemu-img: Could not open 'foo': Could not open 'foo': No such file or directory)
> 
> This change uses error_report_err() instead to eliminate the duplicate part.
> 
> Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
> ---
>  qemu-img.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index 2e40e1f..dc6652d 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -268,7 +268,7 @@ static BlockBackend *img_open_opts(const char *optstr,
>      options = qemu_opts_to_qdict(opts, NULL);
>      blk = blk_new_open(NULL, NULL, options, flags, &local_err);
>      if (!blk) {
> -        error_reportf_err(local_err, "Could not open '%s': ", optstr);
> +        error_report_err(local_err);
>          return NULL;
>      }
>      blk_set_enable_write_cache(blk, !writethrough);
> @@ -295,7 +295,7 @@ static BlockBackend *img_open_file(const char *filename,
>  
>      blk = blk_new_open(filename, NULL, options, flags, &local_err);
>      if (!blk) {
> -        error_reportf_err(local_err, "Could not open '%s': ", filename);
> +        error_report(local_err);
>          return NULL;
>      }
>      blk_set_enable_write_cache(blk, !writethrough);

The duplication happens in the "Could not open 'foo'" case, but other
error cases do not include the filename in the error message.

We would lose information in those error cases since the filename is no
longer included by qemu-img.c in the error message.

I'm not aware of a clean way to distinguish Error objects.  Maybe
someone else can suggest one.  Otherwise it may be best to leave the
code as it is.

Stefan

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