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

[Stefano Garzarella]

On Wed, Feb 24, 2021 at 03:36:20PM +0100, Kevin Wolf wrote:
> 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.

Do you think is better to leave it as it was or do something like this?

    if (job->job.ret) {
        info->has_error = true;
        info->error = job->job.err ? g_strdup(error_get_pretty(job->job.err)) :
                        g_strdup(strerror(-job->job.ret);
    }

Thanks,
Stefano

> >      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