Re: [Qemu-devel] [PATCH v2 09/20] cow: correctly propagate errors

[Jeff Cody <jcody@redhat.com>]

On Fri, Feb 14, 2014 at 05:45:40PM +0100, Kevin Wolf wrote:
> Am 11.02.2014 um 18:03 hat Paolo Bonzini geschrieben:
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> >  block/cow.c | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/block/cow.c b/block/cow.c
> > index 7fc0b12..43a2150 100644
> > --- a/block/cow.c
> > +++ b/block/cow.c
> > @@ -82,7 +82,7 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags,
> >          char version[64];
> >          snprintf(version, sizeof(version),
> >                 "COW version %d", cow_header.version);
> > -        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
> > +        error_set(errp, QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
> >              bs->device_name, "cow", version);
> >          ret = -ENOTSUP;
> >          goto fail;
> > @@ -330,7 +330,6 @@ static int cow_create(const char *filename, QEMUOptionParameter *options,
> >      struct stat st;
> >      int64_t image_sectors = 0;
> >      const char *image_filename = NULL;
> > -    Error *local_err = NULL;
> >      int ret;
> >      BlockDriverState *cow_bs;
> >  
> > @@ -344,18 +343,13 @@ static int cow_create(const char *filename, QEMUOptionParameter *options,
> >          options++;
> >      }
> >  
> > -    ret = bdrv_create_file(filename, options, &local_err);
> > +    ret = bdrv_create_file(filename, options, errp);
> >      if (ret < 0) {
> > -        qerror_report_err(local_err);
> > -        error_free(local_err);
> >          return ret;
> >      }
> >  
> > -    ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR,
> > -                         &local_err);
> > +    ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR, errp);
> >      if (ret < 0) {
> > -        qerror_report_err(local_err);
> > -        error_free(local_err);
> >          return ret;
> >      }
> 
> This is technically correct, but I think general policy is that using
> the local_err pattern is preferred anyway.
>

If I recall correct, I think there are several places that pass errp
along.  How about this for a rule of thumb policy: use the local_err
method if the function does not indicate error outside of the passed
Error pointer.