Re: [PATCH v3 4/4] block: switch to use qemu_open/qemu_create for improved errors

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Jul 24, 2020 at 09:10:00AM -0500, Eric Blake wrote:
> On 7/24/20 8:25 AM, Daniel P. Berrangé wrote:
> > Currently at startup if using cache=none on a filesystem lacking
> > O_DIRECT such as tmpfs, at startup QEMU prints
> > 
> > qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: file system may not support O_DIRECT
> > qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Could not open '/tmp/foo.img': Invalid argument
> 
> Are we trying to get this in 5.1?

It is probably verging on too late to justify for the rc

> 
> > 
> > while at QMP level the hint is missing, so QEMU reports just
> > 
> >    "error": {
> >        "class": "GenericError",
> >        "desc": "Could not open '/tmp/foo.img': Invalid argument"
> >    }
> > 
> > which is close to useless for the end user trying to figure out what
> > they did wrong.
> > 
> > With this change at startup QEMU prints
> > 
> > qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Unable to open '/tmp/foo.img' flags 0x4000: filesystem does not support O_DIRECT
> > 
> > while at the QMP level QEMU reports a massively more informative
> > 
> >    "error": {
> >       "class": "GenericError",
> >       "desc": "Unable to open '/tmp/foo.img' flags 0x4002: filesystem does not support O_DIRECT"
> >    }
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> 
> > @@ -3335,7 +3331,7 @@ static bool setup_cdrom(char *bsd_path, Error **errp)
> >       for (index = 0; index < num_of_test_partitions; index++) {
> >           snprintf(test_partition, sizeof(test_partition), "%ss%d", bsd_path,
> >                    index);
> > -        fd = qemu_open_old(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE);
> > +        fd = qemu_open(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE, NULL);
> 
> Should qemu_open() always be setting O_BINARY|O_LARGEFILE, without us having
> to worry about them at each caller?  But that's a separate cleanup.

Hmm, I think both of these are dead code.

IIUC, O_BINARY  is a no-op on any platform except Windows, and this is
file-posix.c, and O_LARGEFILE is a no-op, if you have _FILE_OFFSET_BITS=64,
which we hardcode.

> Reviewed-by: Eric Blake <eblake@redhat.com>

Regards,
Daniel
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