Re: hald reading block devices

[David Zeuthen <david fubar dk>]

On Mon, 2004-08-23 at 09:12 -0400, Alan Cox wrote:
> > HAL needs to run as root to invoke callouts. See this diagram
> >  http://freedesktop.org/~david/hal-spec/hal-spec.html#ov_hal_linux26
> 
> Needs some rights. Root is kind of going away in SELinux.
> 

Sure.

> > and surrounding text for more information, background etc. Presumably we
> > can move to callouts (such as fstab-sync) to a separate helper process
> > and by then drop a lot of privileges etc. Until that happens we need to
> > run as root because the callouts may need privileges.
> 
> Yep. So all your callouts touch complex shared files with locking rules
> and possible race attacks (or without sane locking rules sometimes).  Hard
> to avoid though
> 

Not anymore; in hal HEAD (will be out in the next release pretty, some
of it is already in the rawhide version) all callouts per device run
sequentially and a device isn't processed before the callouts from the
parent is complete. 

But in general, yeah, if you touch an important file, like /etc/fstab,
you should of course use locking.

> Take a look at how magicdev does things. Magicdev sucks but it does the basic
> open device, unlock door and poll stuff although it doesn't use the newer
> media stuff
> 

Hmm, IIRC hal does basically pretty much the same as magicdev. Would the
newer media stuff mean that we can indeed detect media changes without
ruining everything?

Btw, Alan, please file a bug against hal so we can it to work with your
cd changer or at least make sure that it doesn't screw anything up the
way you describe.

Thanks,
David