Re: [PATCH] blockjob: report a better error message

[Kevin Wolf <kwolf@redhat.com>]

Am 23.02.2021 um 14:11 hat Stefano Garzarella geschrieben:
> When a block job fails, we report 'strerror(-job->job.ret)' error
> message, also if the job set an error object.
> Let's report a better error message using 'error_get_pretty(job->job.err)'.
> 
> If an error object was not set, strerror(-job->ret) is used as fallback,
> as explained in include/qemu/job.h:
> 
> typedef struct Job {
>     ...
>     /**
>      * Error object for a failed job.
>      * If job->ret is nonzero and an error object was not set, it will be set
>      * to strerror(-job->ret) during job_completed.
>      */
>     Error *err;
> }

This is true, but there is a short time where job->ret is already set,
but not turned into job->err yet if necessary. The latter is done in a
bottom half scheduled after the former has happened.

It doesn't matter for block_job_event_completed(), which is called only
after both, but block_job_query() could in theory be called in this
window.

> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  blockjob.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/blockjob.c b/blockjob.c
> index f2feff051d..a696f3408d 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -319,7 +319,8 @@ BlockJobInfo *block_job_query(BlockJob *job, Error **errp)
>      info->auto_finalize = job->job.auto_finalize;
>      info->auto_dismiss  = job->job.auto_dismiss;
>      info->has_error = job->job.ret != 0;
> -    info->error     = job->job.ret ? g_strdup(strerror(-job->job.ret)) : NULL;
> +    info->error     = job->job.ret ?
> +                        g_strdup(error_get_pretty(job->job.err)) : NULL;

So I think we can't rely on job->job.err being non-NULL here.

>      return info;
>  }
>  
> @@ -356,7 +357,7 @@ static void block_job_event_completed(Notifier *n, void *opaque)
>      }
>  
>      if (job->job.ret < 0) {
> -        msg = strerror(-job->job.ret);
> +        msg = error_get_pretty(job->job.err);
>      }
>  
>      qapi_event_send_block_job_completed(job_type(&job->job),

Kevin