Re: [Qemu-devel] [Qemu-block] [PATCH 03/14] job: Add error message for failing jobs

[Kevin Wolf <kwolf@redhat.com>]

Am 29.05.2018 um 16:43 hat Jeff Cody geschrieben:
> On Fri, May 25, 2018 at 06:33:16PM +0200, Kevin Wolf wrote:
> > So far we relied on job->ret and strerror() to produce an error message
> > for failed jobs. Not surprisingly, this tends to result in completely
> > useless messages.
> > 
> > This adds a Job.error field that can contain an error string for a
> > failing job, and a parameter to job_completed() that sets the field. As
> > a default, if NULL is passed, we continue to use strerror(job->ret).
> > 
> > All existing callers are changed to pass NULL. They can be improved in
> > separate patches.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  include/qemu/job.h |  7 ++++++-
> >  block/backup.c     |  2 +-
> >  block/commit.c     |  2 +-
> >  block/mirror.c     |  2 +-
> >  block/stream.c     |  2 +-
> >  job-qmp.c          |  9 ++-------
> >  job.c              | 15 +++++++++++++--
> >  7 files changed, 25 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/qemu/job.h b/include/qemu/job.h
> > index 8c8badf75e..b2e1dd00b9 100644
> > --- a/include/qemu/job.h
> > +++ b/include/qemu/job.h
> > @@ -124,6 +124,9 @@ typedef struct Job {
> >      /** Estimated progress_current value at the completion of the job */
> >      int64_t progress_total;
> >  
> > +    /** Error string for a failed job (NULL if job->ret == 0) */
> > +    char *error;
> > +
> >      /** ret code passed to job_completed. */
> >      int ret;
> >  
> > @@ -466,13 +469,15 @@ void job_transition_to_ready(Job *job);
> >  /**
> >   * @job: The job being completed.
> >   * @ret: The status code.
> > + * @error: The error message for a failing job (only with @ret < 0). If @ret is
> > + *         negative, but NULL is given for @error, strerror() is used.
> >   *
> >   * Marks @job as completed. If @ret is non-zero, the job transaction it is part
> >   * of is aborted. If @ret is zero, the job moves into the WAITING state. If it
> >   * is the last job to complete in its transaction, all jobs in the transaction
> >   * move from WAITING to PENDING.
> >   */
> > -void job_completed(Job *job, int ret);
> > +void job_completed(Job *job, int ret, Error *error);
> >  
> >  /** Asynchronously complete the specified @job. */
> >  void job_complete(Job *job, Error **errp);
> > diff --git a/block/backup.c b/block/backup.c
> > index 4e228e959b..5661435675 100644
> > --- a/block/backup.c
> > +++ b/block/backup.c
> > @@ -321,7 +321,7 @@ static void backup_complete(Job *job, void *opaque)
> >  {
> >      BackupCompleteData *data = opaque;
> >  
> > -    job_completed(job, data->ret);
> > +    job_completed(job, data->ret, NULL);
> >      g_free(data);
> >  }
> >  
> > diff --git a/block/commit.c b/block/commit.c
> > index 620666161b..e1814d9693 100644
> > --- a/block/commit.c
> > +++ b/block/commit.c
> > @@ -117,7 +117,7 @@ static void commit_complete(Job *job, void *opaque)
> >       * bdrv_set_backing_hd() to fail. */
> >      block_job_remove_all_bdrv(bjob);
> >  
> > -    job_completed(job, ret);
> > +    job_completed(job, ret, NULL);
> >      g_free(data);
> >  
> >      /* If bdrv_drop_intermediate() didn't already do that, remove the commit
> > diff --git a/block/mirror.c b/block/mirror.c
> > index dcb66ec3be..435268bbbf 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -581,7 +581,7 @@ static void mirror_exit(Job *job, void *opaque)
> >      blk_set_perm(bjob->blk, 0, BLK_PERM_ALL, &error_abort);
> >      blk_insert_bs(bjob->blk, mirror_top_bs, &error_abort);
> >  
> > -    job_completed(job, data->ret);
> > +    job_completed(job, data->ret, NULL);
> >  
> >      g_free(data);
> >      bdrv_drained_end(src);
> > diff --git a/block/stream.c b/block/stream.c
> > index a5d6e0cf8a..9264b68a1e 100644
> > --- a/block/stream.c
> > +++ b/block/stream.c
> > @@ -93,7 +93,7 @@ out:
> >      }
> >  
> >      g_free(s->backing_file_str);
> > -    job_completed(job, data->ret);
> > +    job_completed(job, data->ret, NULL);
> >      g_free(data);
> >  }
> >  
> > diff --git a/job-qmp.c b/job-qmp.c
> > index 7f38f63336..410775df61 100644
> > --- a/job-qmp.c
> > +++ b/job-qmp.c
> > @@ -136,14 +136,9 @@ void qmp_job_dismiss(const char *id, Error **errp)
> >  static JobInfo *job_query_single(Job *job, Error **errp)
> >  {
> >      JobInfo *info;
> > -    const char *errmsg = NULL;
> >  
> >      assert(!job_is_internal(job));
> >  
> > -    if (job->ret < 0) {
> > -        errmsg = strerror(-job->ret);
> > -    }
> > -
> >      info = g_new(JobInfo, 1);
> >      *info = (JobInfo) {
> >          .id                 = g_strdup(job->id),
> > @@ -151,8 +146,8 @@ static JobInfo *job_query_single(Job *job, Error **errp)
> >          .status             = job->status,
> >          .current_progress   = job->progress_current,
> >          .total_progress     = job->progress_total,
> > -        .has_error          = !!errmsg,
> > -        .error              = g_strdup(errmsg),
> > +        .has_error          = !!job->error,
> > +        .error              = g_strdup(job->error),
> >      };
> >  
> >      return info;
> > diff --git a/job.c b/job.c
> > index f026661b0f..fc39eaaa5e 100644
> > --- a/job.c
> > +++ b/job.c
> > @@ -369,6 +369,7 @@ void job_unref(Job *job)
> >  
> >          QLIST_REMOVE(job, job_list);
> >  
> > +        g_free(job->error);
> >          g_free(job->id);
> >          g_free(job);
> >      }
> > @@ -661,6 +662,9 @@ static void job_update_rc(Job *job)
> >      }
> >      if (job->ret) {
> >          job_state_transition(job, JOB_STATUS_ABORTING);
> > +        if (!job->error) {
> > +            job->error = g_strdup(strerror(-job->ret));
> > +        }
> >      }
> >  }
> >  
> > @@ -855,10 +859,17 @@ static void job_completed_txn_success(Job *job)
> >      }
> >  }
> >  
> > -void job_completed(Job *job, int ret)
> > +void job_completed(Job *job, int ret, Error *error)
> >  {
> >      assert(job && job->txn && !job_is_completed(job));
> > +
> >      job->ret = ret;
> > +    if (error) {
> > +        assert(job->ret < 0);
> 
> The assert here implies that only job->ret values < 0 are valid for error.
> Elsewhere, we just check for non-zero values for error (for example, [1]).
> Maybe we should relax this to just assert(job->ret) here?

A positive error is usually a bug. I wouldn't even be sure if it should
be considered success (e.g. someone returned the result of bdrv_pwrite()
like the two places fixed at the start of this series) or we forgot to
negate errno.

I think it's better to be strict and catch such bugs.

Kevin