svn commit: r365643 - head/bin/cp

[Warner Losh]

On Sat, Sep 26, 2020 at 12:58 PM Benjamin Kaduk <bjkfbsd at gmail.com> wrote:

> On Sat, Sep 26, 2020 at 11:55 AM Warner Losh <imp at bsdimp.com> wrote:
>
>> And there's the rub: how did this file come to exist? I'm certain it isn't
>> booting or shutting down the system based on when devfs is mounted (before
>> init) and unmounted (it's not done by the shutdown scripts). Now, it's
>> always possible there's a hole in my understanding of the sequence of
>> events. But given the examination of code, it's crazy to think this could
>> be created by anything but some weird bug. That's why a step-by-step from
>> scratch guide is needed. Im happy to look into it, but I need a bit more
>> to
>> go on.
>>
>>
> I don't think it's terribly complicated; either set up a multi-boot system
> or
> pull the physical drive with / from one machine, and mount it while booted
> into a different environment.  Then, chroot into it and do ... just about
> anything.
> If you didn't mount devfs before chrooting, then you get a file /dev/null
> (and some
> really confused errors from, e.g., buildworld!).
>

I think there's two different things that are being talked about here.
Let's not confuse the two.

The first is making the build system not depend on /dev/null. You'll find
that's hard to do if you and try to do it since /dev/null is used about 200
times in the current build system in about a dozen different ways. Some are
easy, most are a bit tricky since you can't just close stdout/stderr
because then any files opened by the program will get those FDs and
printf/fprint(stderr, will collide.  This dependency won't be fixed any
time soon, though I could add a seatbelt to buildworld/buildkernel that
ensures that /dev/null is a character device.

The second is a report that /dev/null is created all the time through
normal means before devfs can be mounted.  However, several people have
looked and found no evidence on their system. This means there's something
special / unique to Rod's setup that's generating them (assuming it isn't a
simple chroot without devfs). What that is, and how they come to be, hasn't
been explained in enough detail to reproduce. That's what people are asking
Rod about: how do we get there? How did it happen? Once we know those
answers, we can fix it.

Warner