svn commit: r365643 - head/bin/cp

[Kyle Evans]

On Thu, Sep 24, 2020 at 3:08 AM Stefan Esser <se at freebsd.org> wrote:
>
> Am 24.09.20 um 08:54 schrieb Warner Losh:
> >
> >
> > On Thu, Sep 24, 2020 at 12:41 AM Stefan Esser <se at freebsd.org
> > <mailto:se at freebsd.org>> wrote:
> >
> >     Am 23.09.20 um 19:23 schrieb Warner Losh> But for this issue, we're not
> >     mounting devfs early enough.  We should
> >      > fix that. Removing /dev/null from the boot process likely is
> >     never going
> >      > to happen because we use it all over the place to discard output...
> >      > There's ~200 instances of it in the boot rc scripts, so getting
> >     rid of
> >      > it there would also be quite the effort, with the same question.
> >
> >     Removal of /dev/null from rc.d scripts should be quite simple,
> >     since most cases could just use ">-" (close file descriptor)
> >     instead. Other usage could be substituted with ":>" followed
> >     by chown.
> >
> >
> > So closing fd1 and fd2 doesn't cause them to be available for these
> > programs to get as an fd on open, causing other issues?
> >
> > But >- isn't documented in sh(1) as doing the close thing. On a whim I
> > did the following:
> > $ echo fred >-
> > $ ls -last ./-
> > 4 -rw-r--r--  1 imp  imp  5 Sep 24 00:50 ./-
> > $ cat ./-
> > fred
> > $
> > which suggests maybe you now have a lot of files named - instead...
>
> Yes, sorry, please ignore what I wrote - I was thinking of ">&-" of
> course, but that is not gracefully accepted by many commands (they
> are aborted when trying to write to the closed file descriptor).
>
> I had thought about piping into a command that ignores STDIN, first,
> e.g. "| :", but that generates a SIGPIPE when trying to flush the
> FILE buffer (i.e. after 4 KB, which might be sufficient for most
> cases, but it is not a general solution).
>
> A program that reads from STDIN and generates no output could be used,
> though, e.g. "| sed d".
>
> But this would cause lots of extra forked processes and increase the
> start-up time and is not acceptable.
>
> >     but e.g. rc.d/syscons
> >     uses ${kbddev} (i.e. /dev/ttyv0) and rc.d/zvol performs swapon
> >     on /dev/zvol/${name}, rc.d/random uses /dev/random and so on.
> >
> > So those interactions should be disaled by rc variables...  Or we should
> > be failing the operation...
>
> Going multi-user should not be stopped by any of the rc scripts
> failing due to lack of /dev. But since most developers will only
> test with /dev available, there is a risk that changes to rc files
> will not gracefully handle a missing /dev.
>

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.

I agree with the previous goal of ripping the /dev dependency out of
the build, but this is also much, much easier said than done.