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

[Kevin Wolf]

Am 24.02.2021 um 16:59 hat Stefano Garzarella geschrieben:
> 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);
>     }

Yes, I think this is the best solution. Use the error when we have it,
fall back to strerror() when we don't have it.

Kevin