svn commit: r365643 - head/bin/cp

[Rodney W. Grimes]

> 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.

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.

> 
> 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.
> 

So we agree that it might be a good idea to reduce /dev
dependency in the build process.


-- 
Rod Grimes                                                 rgrimes at freebsd.org