Re: [PATCH] block: Remove trailing newline in format used by error_report API

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 2/28/20 6:32 PM, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <philmd@redhat.com> writes:
> 
>> The error_report API doesn't want trailing newline characters.
>> Remove it, to avoid and error when moving the code around:
>>
>>   ERROR: Error messages should not contain newlines
> 
> Commit 312fd5f2909 has a Coccinelle script.  It should be committed and
> re-run.
> 
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>  block.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block.c b/block.c
>> index 1bdb9c679d..e466d15914 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -5994,7 +5994,7 @@ void bdrv_img_create(const char *filename, const char *fmt,
>            bs = bdrv_open(full_backing, NULL, backing_options, back_flags,
>                           &local_err);
>            g_free(full_backing);
>            if (!bs && size != -1) {
>>              /* Couldn't open BS, but we have a size, so it's nonfatal */
>>              warn_reportf_err(local_err,
>>                              "Could not verify backing image. "
>> -                            "This may become an error in future versions.\n");
>> +                            "This may become an error in future versions.");
>>              local_err = NULL;
>>          } else if (!bs) {
>>              /* Couldn't open bs, do not have size */
> 
> warn_reportf_err() is a convenience function to error_prepend(),
> warn_report() and free @local_err.

OK now I see.

Why warn_reportf_err() doesn't take a 'Error **err' instead, to set err
to NULL after freeing *err?

> 
> When @local_err holds a message like "pants on fire", the code before
> the patch prints something like
> 
>     qemu-system-x86_64: warning: Could not verify backing image. This may become an error in future versions.
>     pants on fire
> 
> The patch "improves" it to
> 
>     qemu-system-x86_64: warning: Could not verify backing image. This may become an error in future versions.pants on fire
> 
> General advice: this misuse of warn_reportf_err() is an excusable
> mistake, but when you *test* the error path, you can't *not* see that
> the actual message is crap.  Test your errors!
> 
> Actual improvement:
> 
>                warn_reportf_err(local_err, "Could not verify backing image: ");
>                error_printf("This may become an error in future versions.\n");
> 
> This should print
> 
>     qemu-system-x86_64: warning: Could not verify backing image: pants on fire
>     This may become an error in future versions.
>