Re: [Qemu-devel] [GSoC 2010] Pass-through filesystem support.

From: Alexander Graf <agraf@suse.de>
To: Mohammed Gamal <m.gamal005@gmail.com>
Cc: Jamie Lokier <jamie@shareable.org>,
	Anthony Liguori <aliguori@us.ibm.com>,
	Cam Macdonell <cam@cs.ualberta.ca>,
	qemu-devel@nongnu.org, kvm-devel <kvm@vger.kernel.org>,
	Javier Guerra Giraldez <javier@guerrag.com>
Subject: Re: [Qemu-devel] [GSoC 2010] Pass-through filesystem support.
Date: Mon, 12 Apr 2010 10:59:45 +0200	[thread overview]
Message-ID: <4D687A08-BD58-4484-8BCC-90B81DE842F1@suse.de> (raw)
In-Reply-To: <s2z52d4a3891004120115j7c0cf886mfe2e9f0e94417d5@mail.gmail.com>

On 12.04.2010, at 10:15, Mohammed Gamal wrote:

> On Mon, Apr 12, 2010 at 12:29 AM, Jamie Lokier <jamie@shareable.org> wrote:
>> Javier Guerra Giraldez wrote:
>>> On Sat, Apr 10, 2010 at 7:42 AM, Mohammed Gamal <m.gamal005@gmail.com> wrote:
>>>> On Sat, Apr 10, 2010 at 2:12 PM, Jamie Lokier <jamie@shareable.org> wrote:
>>>>> To throw a spanner in, the most widely supported filesystem across
>>>>> operating systems is probably NFS, version 2 :-)
>>>> 
>>>> Remember that Windows usage on a VM is not some rare use case, and
>>>> it'd be a little bit of a pain from a user's perspective to have to
>>>> install a third party NFS client for every VM they use. Having
>>>> something supported on the VM out of the box is a better option IMO.
>>> 
>>> i don't think virtio-CIFS has any more support out of the box (on any
>>> system) than virtio-9P.
>> 
>> It doesn't, but at least network-CIFS tends to work ok and is the
>> method of choice for Windows VMs - when you can setup Samba on the
>> host (which as previously noted you cannot always do non-disruptively
>> with current Sambas).
>> 
>> -- Jamie
>> 
> 
> I think having support for both 9p and CIFS would be the best option.
> In that case the user will have the option to use either one,
> depending on how their guests support these filesystems. In that case
> I'd prefer to work on CIFS support while the 9p effort can still go
> on. I don't think both efforts are mutually exclusive.

I think that the 9p support is handled by the IBM guys pretty well already. They do need help, but I doubt they need as much help as a full GSoC student. You're definitely free to help them out regardless of GSoC :-).

As far as CIFS goes - we currently do use CIFS in the SUSE Studio infrastructure as data interface between host and build guests. About 80% of all backend bugs resulted from that decision. It just breaks in the most ridiculous ways. Just a few examples from our commit log:

  - loopback mounts on CIFS break after heavy I/O
  - moving symlinks fails
  - does not allow ':' in file names

So we're currently waiting for 9p eagerly, as that at least gives us easy control over the stack. And it's a lot less complicated.

Also since -net user does support samba exporting already, I don't see that much value in adding it. I'd rather like to see a virtio-9p driver for Windows.

Alex