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Re: [Qemu-devel] [PATCH 3/9] block: bdrv_reopen_prepare(): use error_set
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 3/9] block: bdrv_reopen_prepare(): use error_setg_file_open() |
Date: |
Mon, 10 Jun 2013 15:54:10 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 10.06.2013 um 15:21 hat Luiz Capitulino geschrieben:
> On Mon, 10 Jun 2013 10:43:47 +0200
> Stefan Hajnoczi <address@hidden> wrote:
>
> > On Fri, Jun 07, 2013 at 03:52:29PM -0400, Luiz Capitulino wrote:
> > > Signed-off-by: Luiz Capitulino <address@hidden>
> > > ---
> > > 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?
errno is definitely not reliable here and won't be. You must use -ret if
you want a meaningful error message.
I think Stefan's point was more that "Could not open" might not be the
right message for a reopen, so we'd have to use error_setg_errno()
directly with a different message here, like "Could not prepare reopen
for '%s'".
The _real_ solution, of course, is to make bdrv_prepare_reopen() a void
function and always set errp when something goes wrong.
Kevin
[Qemu-devel] [PATCH 5/9] blockdev: use error_setg_file_open(), Luiz Capitulino, 2013/06/07
[Qemu-devel] [PATCH 6/9] cpus: use error_setg_file_open(), Luiz Capitulino, 2013/06/07
[Qemu-devel] [PATCH 7/9] dump: qmp_dump_guest_memory(): use error_setg_file_open(), Luiz Capitulino, 2013/06/07
[Qemu-devel] [PATCH 8/9] savevm: qmp_xen_save_devices_state(): use error_setg_file_open(), Luiz Capitulino, 2013/06/07
[Qemu-devel] [PATCH 9/9] qerror: drop QERR_OPEN_FILE_FAILED macro, Luiz Capitulino, 2013/06/07