Re: [Qemu-devel] [PATCH 3/9] block: bdrv_reopen_prepare(): use error_setg_file_open()

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 10 Jun 2013 10:43:47 +0200
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Fri, Jun 07, 2013 at 03:52:29PM -0400, Luiz Capitulino wrote:
> > Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> > ---
> >  block.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/block.c b/block.c
> > index 79ad33d..c78f152 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -1291,8 +1291,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
> >              if (local_err != NULL) {
> >                  error_propagate(errp, local_err);
> >              } else {
> > -                error_set(errp, QERR_OPEN_FILE_FAILED,
> > -                          reopen_state->bs->filename);
> > +                error_setg_file_open(errp, errno, reopen_state->bs->filename);
> 
> Looking closer, my suggestion was wrong too.
> 
> I think QERR_OPEN_FILE_FAILED is simply the wrong error here.  We don't
> know that the error occurred when trying to open a file.

Right.

> errno does not necessarily contain the error value!

There are two ways to fix it (and they're not mutually exclusive):

 1. We could review all bdrv_reopen_prepare() methods and make sure they
    set errno on failure

 2. We set errno=0 before calling the bdrv_reopen_prepare() method and if
    there's an error and if errno != 0 we use it, otherwise we set a generic
    "failed to prepare to reopen image" error

Option 1 goes a bit beyond the time I'd like to spent on this series.
Option 2 is quite reasonable.

What do you think?