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

[Jeff Cody <jcody@redhat.com>]

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().