[PATCH] was: mdev doesn't remove devices

[Jason Schoon]

On 8/29/06, Rob Landley <rob at landley.net> wrote:
>
> On Monday 28 August 2006 5:21 pm, Jason Schoon wrote:
> > Since we're on the topic of mdev already, I have a patch I had to create
> > today that I thought I would run by the list.
> >
> > I am using mdev with a mdev.conf to launch a script file in certain
> cases
> > (basically it enables hotplugging on USB flash devices for me).
> >
> > In that script, I happened to add a line that sends its output to
> /dev/null
> > (i.e. 2>/dev/null).  Well, this just so happens to create an empty file,
> > which then causes mknod of /dev/null to fail with an "already exists."
>
> You're calling this from a hotplug script that's called before /dev/null
> exists.  This really sounds like pilot error to me.
>
> > So, my solution was to either make sure that my hotplug script never,
> ever
> > talks to a dev file (a poor assumption I feel),
>
> You're creating your devices via hotplug and you want to assume that
> random
> devices have already been created?
>
> > or to patch mdev to check if
> > something is a regular file, and delete it.  Attached is a patch that
> > accomplishes just that.  If someone else thinks that is a sane thing to
> do,
> > please apply.
>
> Isn't this really a special case for /dev/null?  Why not mknod /dev/null
> from
> your init script if your hotplug scripts are going to assume it exists
> before
> the hotplug scripts have been called?
>
> If you don't want to build in mknod, you can get mdev to do it:
>
>   ACTION=add DEVPATH=/sys/class/mem/null mdev
>
> Rob
>

/dev/null already exists.  I call mdev -s at system startup to populate my
initial set of devices.  The real problem is that in my mdev.conf I call out
to a script that redirects some output to /dev/null.  Everytime mdev -s
executed, it recreated a bogus /dev/null, and then when the mdev code itself
tried to do the mknod, it returns an EEXIST.

There are a lot of other ways I can prevent the problem.  I couldn't think
of a valid reason for a regular file to exist in /dev though, so I thought
this could be a generic sledgehammer fix, at the cost of a call to stat().
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