linux-kernel - Re: [PATCH] net/9p: autoload transport modules

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Date:   Tue, 2 Nov 2021 16:32:21 +0100
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/9p: autoload transport modules

On 2021-11-02 23:58+0900, Dominique Martinet wrote:
> Thomas Weißschuh wrote on Tue, Nov 02, 2021 at 03:49:32PM +0100:
> > > I guess it wouldn't hurt to have 9p-tcp 9p-unix and 9p-fd aliases to the
> > > 9pnet module, but iirc these transports were more closely tied to the
> > > rest of 9pnet than the rest so it might take a while to do and I don't
> > > have much time for this right now...
> > > I'd rather not prepare for something I'll likely never get onto, so
> > > let's do this if there is progress.
> > > 
> > > Of course if you'd like to have a look that'd be more than welcome :-)
> > 
> > If you are still testing anyways, you could also try the attached patch.
> > (It requires the autload patch)
> > 
> > It builds fine and I see no reason for it not to work.
> 
> Thanks! I'll give it a spin.
> 
> 
> I was actually just testing the autoload one and I can't get it to work
> on my minimal VM, I guess there's a problem with the usermodhelper call
> to load module..
> 
> with 9p/9pnet loaded,
> running "mount -t 9p -o trans=virtio tmp /mnt"
> request_module("9p-%s", "virtio") returns -2 (ENOENT)

Can you retry without 9p/9pnet loaded and see if they are loaded by the mount
process?
The same autoloading functionality exists for filesystems using
request_module("fs-%s") in fs/filesystems.c
If that also doesn't work it would indicate an issue with the kernel setup in general.

> Looking at the code it should be running "modprobe -q -- 9p-virtio"
> which finds the module just fine, hence my supposition usermodhelper is
> not setup correctly
> 
> Do you happen to know what I need to do for it?

What is the value of CONFIG_MODPROBE_PATH?
And the contents of /proc/sys/kernel/modprobe?

> I've run out of time for today but will look tomorrow if you don't know.
> 
> (And since it doesn't apparently work out of the box on these minimal
> VMs I think I'll want the trans_fd module split to sit in linux-next
> for a bit longer than a few days, so will be next merge window)

Sure.

Thomas