Re: [Qemu-devel] [PATCH 2/2] osdep: warn if open(O_DIRECT) on fails with EINVAL

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Sep 06, 2013 at 04:32:43PM -0400, Jeff Cody wrote:
> On Thu, Aug 22, 2013 at 11:29:03AM +0200, Stefan Hajnoczi wrote:
> > Print a warning when opening a file O_DIRECT fails with EINVAL.  This
> > saves users a lot of time trying to figure out the EINVAL error, which
> > is typical when attempting to open a file O_DIRECT on Linux tmpfs.
> > 
> > Reported-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> >  util/osdep.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/util/osdep.c b/util/osdep.c
> > index 685c8ae..62072b4 100644
> > --- a/util/osdep.c
> > +++ b/util/osdep.c
> > @@ -207,6 +207,13 @@ int qemu_open(const char *name, int flags, ...)
> >      }
> >  #endif
> >  
> > +#ifdef O_DIRECT
> > +    if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
> > +        error_report("file system may not support O_DIRECT");
> > +        errno = EINVAL; /* in case it was clobbered */
> > +    }
> > +#endif /* O_DIRECT */
> > +
> >      return ret;
> >  }
> >  
> > -- 
> > 1.8.3.1
> > 
> > 
> 
> What about putting something similar in error_setg_file_open(), in
> util/error.c?  There are other occasions when O_DIRECT causes a file
> open to fail (e.g. live snapshots with 'cache=none' to a tmpfs
> filesystem).  That would give additional info then for QMP commands.
> Of course, it would then be necessary to also pass the open flags (or
> other equivalent info) to error_setg_file_open().

It would be nice to cover all file open cases.  But I think
error_setg_file_open() is a bit beyond the scope here.

error_setg_file_open() is not used in cases where O_DIRECT is relevant.
I checked all callers and they don't seem to allow O_DIRECT.  Some of
them even use qemu_fopen().

Stefan