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

[Mohammed Gamal]

On Tue, Apr 20, 2010 at 12:54 AM, jvrao <address@hidden> wrote:
> Mohammed Gamal wrote:
>> On Tue, Apr 13, 2010 at 9:08 PM, jvrao <address@hidden> wrote:
>>> jvrao wrote:
>>>> Alexander Graf wrote:
>>>>> On 12.04.2010, at 13:58, Jamie Lokier wrote:
>>>>>
>>>>>> Mohammed Gamal wrote:
>>>>>>> On Mon, Apr 12, 2010 at 12:29 AM, Jamie Lokier <address@hidden> wrote:
>>>>>>>> Javier Guerra Giraldez wrote:
>>>>>>>>> On Sat, Apr 10, 2010 at 7:42 AM, Mohammed Gamal <address@hidden> 
>>>>>>>>> wrote:
>>>>>>>>>> On Sat, Apr 10, 2010 at 2:12 PM, Jamie Lokier <address@hidden> 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.
>>>>>>>
>>>>>>> What do the rest of you guys think?
>>>>>> I only noted NFS because most old OSes do not support CIFS or 9P -
>>>>>> especially all the old unixes.
>>>>>>
>>>>>> I don't think old versions of MS-DOS and Windows (95, 98, ME, Nt4?)
>>>>>> even support current CIFS.  They need extra server settings to work
>>>>>> - such as setting passwords on the server to non-encrypted and other 
>>>>>> quirks.
>>>>>>
>>>>>> Meanwhile Windows Vista/2008/7 works better with SMB2, not CIFS, to
>>>>>> properly see symlinks and hard links.
>>>>>>
>>>>>> So there is no really nice out of the box file service which works
>>>>>> easily with all guest OSes.
>>>>>>
>>>>>> I'm guessing that out of all the filesystems, CIFS is the most widely
>>>>>> supported in recent OSes (released in the last 10 years).  But I'm not
>>>>>> really sure what the state of CIFS is for non-Windows, non-Linux,
>>>>>> non-BSD guests.
>>>>> So what? If you want to have direct host fs access, install guest 
>>>>> drivers. If you can't, set up networking and use CIFS or NFS or whatever.
>>>>>
>>>>>> I'm not sure why 9P is being pursued.  Does anything much support it,
>>>>>> or do all OSes except quite recent Linux need a custom driver for 9P?
>>>>>> Even Linux only got the first commit in the kernel 5 years ago, so
>>>>>> probably it was only about 3 years ago that it will have begun
>>>>>> appearing in stable distros, if at all.  Filesystem passthrough to
>>>>>> Linux guests installed in the last couple of years is a useful
>>>>>> feature, and I know that for many people that is their only use of
>>>>>> KVM, but compared with CIFS' broad support it seems like quite a
>>>>>> narrow goal.
>>>>> The goal is to have something simple and fast. We can fine-tune 9P to 
>>>>> align with the Linux VFS structures, making it really little overhead 
>>>>> (and little headache too). For Windows guests, nothing prevents us to 
>>>>> expose yet another 9P flavor. That again would be aligned well with 
>>>>> Windows's VFS and be slim and fast there.
>>>>>
>>>>> The biggest problem I see with CIFS is that it's a huge beast. There are 
>>>>> a lot of corner cases where it just doesn't fit in. See my previous mail 
>>>>> for more details.
>>>>>
>>>> As Alex mentioned, 9P is chosen for its mere simplicity and easy 
>>>> adaptability.
>>>> NFS and CIFS does not give that flexibility. As we mentioned in the patch 
>>>> series, we are
>>>> already seeing better numbers with 9P. Looking ahead 9P can embed KVM/QEMU 
>>>> knowledge
>>>> to share physical resources like memory/cache between the host and the 
>>>> guest.
>>>>
>>>> I think looking into the windows side of 9P client would be great option 
>>>> too.
>>>> The current patch on the mailing list supports .U (unix) protocol and will 
>>>> be introducing
>>>> .L (Linux) variant as we move forward.
>>> Hi Mohammed,
>>> Please let us know once you decide on where your interest lies.
>>> Will be glad to have you on VirtFS (9P) though. :)
>>>
>>>
>>> - JV
>>>
>>
>> It seems the community is more keen on getting 9P support merged than
>> getting CIFS supported, and they have made good points to support
>> their argument. I'm not sure whether work on this project could fit in
>> as a GSoC project and if there is much remaining work that could make
>> it fit in that direction. But I'd be glad to volunteer anyway :)
>
> I was thinking over the wk-end what fits your schedule and your interest 
> areas. :)
>
> One thing I can think of is, making NFS server export VirtFS mount on the 
> guest to
> the external world. This works fine now if we enable loose cache option in 9P 
> mount.
> But I think we should identify and make this exports work even otherwise.
> Please let me know if this is something that you want to sign up. :)
>
> Thanks,
> JV
>

This'd be something interesting to do. I wonder if that would fit in
the GSoC timeframe, or whether it'd be a little too short. So how long
you'd estimate something like that would take?

Regards,
Mohammed