[Toybox] pull: fix modprobe, login, switch_root, improve init, reboot

[Isaac Dunham]

On Thu, Oct 01, 2015 at 04:42:34AM -0500, Rob Landley wrote:
> Still going through old posts, I'm up to:
> 
> On 08/09/2015 12:24 AM, Isaac Dunham wrote:
> >>> > > If hard-coding "modprobe -bq $MODALIAS" int mdev is desireable, I can send
> >>> > > that; but I suspect it's not quite fit for inclusion.
> >> > 
> >> > I'd be interested in seeing the patch.
> > Attached!
> > 
> > Thanks,
> > Isaac Dunham
> > 
> >>From 0acde7ff07603e7b485bc19ec4a49b3010c49966 Mon Sep 17 00:00:00 2001
> > From: Isaac Dunham <ibid.ag at gmail.com>
> > Date: Mon, 3 Aug 2015 13:28:36 -0700
> > Subject: [PATCH] mdev: autoload modules on hotplug.
> > 
> > ---
> >  toys/pending/mdev.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/toys/pending/mdev.c b/toys/pending/mdev.c
> > index a13a53d..b273d4a 100644
> > --- a/toys/pending/mdev.c
> > +++ b/toys/pending/mdev.c
> > @@ -58,6 +58,8 @@ static void make_device(char *path)
> >    } else {
> >      // if (!path), do hotplug
> >  
> > +    if ((temp = getenv("MODALIAS")))
> > +      xexec((char *[]){"modprobe", temp, 0});
> >      if (!(temp = getenv("SUBSYSTEM")))
> >        return;
> >      type = strcmp(temp, "block") ? S_IFCHR : S_IFBLK;
> 
> The problem here is that does xexec, which is an exec so it replaces the
> current process, meaning the rest of processing doesn't happen.
> 
> Do you mean xrun() maybe? (Spawns child process and waits for it to
> return, reporting exit code.) Or is modalias really the only thing this
> call is expected to do?
 
(This was a preliminary patch that works for me but might not be
appropriate for upstream.)

modprobe $MODALIAS is the only thing this is expected to do.
As far as I know (which is not very far), there are no cases where a single
uevent calls for loading a module and creating a device.

I suppose that it's improper to rely on that without finding docs;
but it somehow seems wrong to do a fully blocking call to modprobe, and
serially with that check if we need to create a device.

Maybe (1) try to fork(); (2) if we succeed, xexec() modprobe; (3) do the
whole mknod/chmod/... bit if appropriate; (4) on completion of that,
call wait().
Note that a forkbomb, which could temporarily result in fork() failing,
should not make the hotplugger die if it's long-running. Making module
loading fail temporarily seems like it would be better.

> (I note that I have a todo item to implement demon mode doing the
> netlink thing, in which case xexec() would again be the wrong thing...)

Agreed. But then, wouldn't xrun() also be the wrong thing?


Thanks,
Isaac Dunham

 1443753265.0