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

[Jamie Lokier]

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.

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.

-- Jamie