Re: [PATCH 1 of 3] If Xen backend modules are not loaded, load them before starting Xend

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2009-12-22 at 19:57 +0000, Konrad Rzeszutek Wilk wrote: 
> On Tue, Dec 22, 2009 at 07:41:17PM +0000, Ian Campbell wrote:
> > On Tue, 2009-12-22 at 16:48 +0000, Konrad Rzeszutek Wilk wrote:
> > > @@ -28,6 +28,7 @@
> > >       grep '    xenfs$' /proc/filesystems >/dev/null && \
> > >     ! grep '^xenfs ' /proc/mounts >/dev/null;
> > >  then
> > > +       modprobe -q xenfs
> > >         mount -t xenfs xenfs /proc/xen
> > >  fi
> > >   
> > 
> > I think this one gets requested automatically if the filesystem isn't
> > currently present, see the call to request_module in
> > fs/filesystems.c:get_fs_type()
> 
> Hmm, in 2.6.32 it looks to be usuable only once the filesystem has
> loaded. This patch is for the case where the filesystem (xenfs) is compiled
> as a module - and had not been loaded. Hence hadn't had a chance to call
> fs/filesystem.c:register_filesystem().

Are you looking at __get_fs_type() and not get_fs_type()? The later is: 
        struct file_system_type *get_fs_type(const char *name)
        {
                struct file_system_type *fs;
                const char *dot = strchr(name, '.');
                int len = dot ? dot - name : strlen(name);
        
                fs = __get_fs_type(name, len);
                if (!fs && (request_module("%.*s", len, name) == 0))
                        fs = __get_fs_type(name, len);
        ....

So either the module is already loaded (or its statically compiled) or
it calls request_module to cause it to become loaded and the second
__get_fs_type succeeds. 

> Thought maybe I messing up this up. The "grep 'xenfs$' /proc/filesystem" checks
> for xenfs in /proc/filesystem so it should not even get to the "then" statement.

Yes, the script looks wrong to me before your patch as well, the check
of /proc/filesystem should be removed.

> Something is fishy here. Why don't we skip this patch and I will revist it
> after holidays.
> 

OK

Ian.