Date: Thu, 24 Sep 2020 07:19:03 -0500 From: Kyle Evans <kevans@freebsd.org> To: Stefan Esser <se@freebsd.org> Cc: Warner Losh <imp@bsdimp.com>, "Rodney W. Grimes" <rgrimes@freebsd.org>, Alan Somers <asomers@freebsd.org>, Mateusz Guzik <mjguzik@gmail.com>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r365643 - head/bin/cp Message-ID: <CACNAnaEzjd6JpS3Ruqct5B%2BQg3mNfvc7QNc2dOFg15NA3Fpzkg@mail.gmail.com> In-Reply-To: <545173d1-a6e1-333a-11c1-a791bbeadd76@freebsd.org> References: <CACNAnaH-L%2Bw=SJW1Cw1M63LQi19d%2Bf_8Sv%2BdYUTyE%2BjYQU6nbA@mail.gmail.com> <202009231656.08NGujEs042900@gndrsh.dnsmgr.net> <CANCZdfoDpG85jSYs36-oWpxwYymTnVJ2dpAXyk9%2B3Ps7enODmw@mail.gmail.com> <fc0903cf-fd1f-1c39-13f0-4902c5bc1cd9@freebsd.org> <CANCZdfpHfRK6Hm8H6%2BUcSyo-jVaTYXjpF7M1NRNqoJmQ4w5xJA@mail.gmail.com> <545173d1-a6e1-333a-11c1-a791bbeadd76@freebsd.org>
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On Thu, Sep 24, 2020 at 3:08 AM Stefan Esser <se@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@freebsd.org
> > <mailto:se@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.
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