From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:53142)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <jcody@redhat.com>) id 1VI2i7-00012Z-3t
	for qemu-devel@nongnu.org; Fri, 06 Sep 2013 16:33:01 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <jcody@redhat.com>) id 1VI2i1-0004Nu-54
	for qemu-devel@nongnu.org; Fri, 06 Sep 2013 16:32:55 -0400
Received: from mx1.redhat.com ([209.132.183.28]:14808)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <jcody@redhat.com>) id 1VI2i0-0004N9-T5
	for qemu-devel@nongnu.org; Fri, 06 Sep 2013 16:32:49 -0400
Date: Fri, 6 Sep 2013 16:32:43 -0400
From: Jeff Cody <jcody@redhat.com>
Message-ID: <20130906203243.GA16486@localhost.localdomain>
References: <1377163743-25029-1-git-send-email-stefanha@redhat.com>
	<1377163743-25029-3-git-send-email-stefanha@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1377163743-25029-3-git-send-email-stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 2/2] osdep: warn if open(O_DIRECT) on fails
 with EINVAL
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Deepak C Shetty <deepakcs@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@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().