Module auto-unloading (was Re: CVS commit: src/sys/arch/x86/x86)

[Jared McNeill <jmcneill%invisible.ca@localhost>]

We could use the reference counter in struct cfdriver to keep driver 
modules "busy", but I'm not sure if the system can figure out what's 
unneeded if a "needed" driver might be one for a hotpluggable device. 
Would you treat those drivers differently? What about drivers (if_ath_pci 
comes to mind) that can be used both for fixed or hotplug devices?

I played around with driver module autoloading a while back, and it worked 
pretty well but the implementation I came up with required duplicating 
match data in <module>.plist.

On Tue, 18 Oct 2011, Warner Losh wrote:

> On Oct 18, 2011, at 4:39 AM, Jared McNeill wrote:
> > I would argue that any manually loaded module shouldn't be autounloaded. What 
> > do you think about flagging modules as autoloaded and only autounloading the 
> > autoloaded ones?
>
> If I "manually" load a dozen drivers at boot because I have a dozen different boards with 
> different devices.  I'd kinda like the system to "automatically" figure out what isn't 
> needed and unload those drivers.
>
> Warner
>
> > On Tue, 18 Oct 2011, Jukka Ruohonen wrote:
> >
> > > On Tue, Oct 18, 2011 at 08:43:46AM +0200, Marc Balmer wrote:
> > > > Am 18.10.11 06:27, schrieb Jukka Ruohonen:
> > > > > On Tue, Oct 18, 2011 at 12:07:45AM +0000, Jared D. McNeill wrote:
> > > > > > Module Name:    src
> > > > > > Committed By:   jmcneill
> > > > > > Date:           Tue Oct 18 00:07:45 UTC 2011
> > > > > >
> > > > > > Modified Files:
> > > > > >         src/sys/arch/x86/x86: vmt.c
> > > > > >
> > > > > > Log Message:
> > > > > > don't allow module autounload
> > > > >
> > > > > I wonder should autounloading be prohibited for all driver-class modules?
> > > >
> > > > Why?  When the parent goes away, why not autounload a driver?
> > >
> > > I am not sure. But have we thought about all the consequences and corner-
> > > cases? Unloading happens while modifying hardware state? Deferred calls
> > > in the drivers? And so on? To me it also seems that if I manually load
> > > a driver-module, I expect it to stay loaded until I unload it.
> > >
> > > - Jukka.