From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Wolf Subject: Re: cifs: Strange O_DIRECT behaviour on non-directio mounts Date: Wed, 16 Jul 2014 21:23:29 +0200 Message-ID: <20140716192329.GD8802@noname.redhat.com> References: <20140627111412.GC5223@noname.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" To: Steve French Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-cifs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Am 16.07.2014 um 20:15 hat Steve French geschrieben: > What is the server type? (you can view this by seeing the "NOS" field > in /proc/fs/cifs/DebugData or checking to see if "unix" is listed in > the mount when you do "cat /proc/mounts | grep cifs") > > When mounted to Samba for example, with cifs unix extensions > negotiated, the cifs client will send open flags (including O_DIRECT > IIRC) to the server on open. When mounted to Windows/NetApp etc. or > when using "nounix" on mount, the flag is not sent on open. As I wrote, this was another user whose problem I debugged over IRC, and he doesn't seem to be available any more, so I can't get any new information from him. What I do have is the line that 'mount' outputs: [12:08:21] kwolf: this is what is shown by mount: //192.168.128.200/storage-cs on /var/lib/one/datastores/107 type cifs (rw,username=yy,password=xx,iocharset=utf8,file_mode=0777,dir_mode=0777) The other information that I have is an strace snippet of the qemu process that tried using a file with O_DIRECT, but no directio mount option. open("/var/lib/one//datastores/1/4131/disk.0", O_RDWR|O_DIRECT|O_CLOEXEC) = 6 [...] pread(6, 0x7f2512bae200, 4096, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512bae400, 4096, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512bae800, 4096, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512baf000, 4096, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512badda0, 512, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512badda0, 1024, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512badda0, 2048, 0) = -1 EINVAL (Invalid argument) pread(6, 0x7f2512badda0, 4096, 0) = -1 EINVAL (Invalid argument) write(2, "qemu-system-x86_64: /build/build"..., 129qemu-system-x86_64: /build/buildd/qemu-2.0.0+dfsg/block.c:942: bdrv_open_common: Assertion `bdrv_opt_mem_align(bs) != 0' failed. ) = 129 Note that remounting with the 'cache=none' mount option, the reporter could successfully use the file even with O_DIRECT. This and the commit message of dca69288 made me think that this is not related to the server, but a client side issue. Kevin > On Fri, Jun 27, 2014 at 6:14 AM, Kevin Wolf wrote: > > Hi Steve, > > > > I just discussed a problem with a qemu user on IRC, which boiled down to > > him trying to open an image file on cifs with O_DIRECT, but not using a > > directio mount. I understand that this probably isn't going to work > > anytime soon (if at all), but it resulted in a rather unhelpful failure > > mode. > > > > What happens is that cifs lets the open() call succeed even with the > > unsupported O_DIRECT on that mount, but then fails any I/O on the file > > descriptor. I believe this was introduced in commit dca69288 (which I > > think is otherwise pretty useful). > > > > With the old behaviour, qemu detected what's going on and suggested to > > use a non-O_DIRECT mode to the user, but with the new one, it got rather > > unhappy after failing to find a working O_DIRECT alignment and ran into > > an assertion failure... > > > > Now I'll certainly fix the latter in qemu, but I also think that the > > behaviour of cifs is rather surprising. Any chance that you can make > > open() with O_DIRECT fail again on non-directio mounts? > > > > Thanks, > > Kevin > > > > -- > Thanks, > > Steve