svn commit: r365643 - head/bin/cp

[Rodney W. Grimes]

> On Fri, 2020-09-25 at 10:55 -0700, Rodney W. Grimes wrote:
> > > I was under the impression from previous reading and kib's response
> > > that this is a complete non-issue, there's no way you can go
> > > multi-user without a mounted /dev and we go to somewhat great
> > > lengths to make sure we're good.
> > 
> > Though kib can assert that, it does not change the fact that I
> > frequently find /dev/null FILES on unmounted root file systems.
> > 
> > But lets not mix the 2 separate things of boot time /dev dependency
> > and build time /dev dependency.
> 
> If you look in sys/kern/vfs_mountroot.c you can see that the code to
> mount /dev is invoked unconditionally as the first step of mounting
> root, and that all the calls it makes to get devfs mounted have their
> results checked with KASSERTs.
> 
> That's pretty strong evidence that devfs is mounted before rc scripts
> run.  That creates a situation where you are making an extraordinary
> claim, so you need to provide extraordinary evidence to support it.  A
> sequence of actions that allows others to recreate the situation would
> do the trick.

I have provided ways one can look for this file in
other messages of the threads.  A dump of a UFS root
can show it up, and iirc you can find it in a
zfs send of a boot dataset.

> 
> (A question that occurs to me:  could it be that the files you've seen
> got created at shutdown after devfs was unmounted, rather than at
> startup?  I don't know enough about the shutdown sequence to know
> whether that's possible.)

Its not "the files" it is "a file, /dev/null".  And yes, it could
be very possible that it is during shutdown.  Sadly the files is
usually of 0 length so leave little clue as to what is creating them.

> -- Ian
-- 
Rod Grimes                                                 rgrimes at freebsd.org