svn commit: r365643 - head/bin/cp

[Rodney W. Grimes]

> On Wed, Sep 23, 2020 at 11:23:51AM -0600, Warner Losh wrote:
> > On Wed, Sep 23, 2020, 10:56 AM Rodney W. Grimes <freebsd at gndrsh.dnsmgr.net>
> > wrote:
> > 
> > > > cp is already fixed, people are still feeling the fallout of being
> > > > within those revisions and needing to bootstrap their own cp. We can
> > > > reduce the number of components these invocations rely on trivially to
> > > > shell built-in mechanics, why not do so?
> > >
> > > I would even go further, I would like to see the dependency on
> > > /dev/null removed from the build, and the boot process.
> > >
> > 
> > A worthy goal, but one I'm afraid is out of our reach. A quick grep shows
> > just over 200 instances of /dev/null in the Makefile and mk file (800 if
> > you don't filter Makefile.in and Makefile.am). Maybe a third of those are
> > due to tests and other false positives. It would be quite the effort to
> > eliminate them all. And /dev/tty and /dev/zero likely will be troublesome
> > too, as they are used by running programs.
> > 
> > and how would you throw away output you know is bad / bogus without
> > /dev/null?
> > 
> > >From the build because it means I would no longer have to
> > > mount /dev in my chroots, and from the boot because I
> > > hate to say it, but we often scribble in /dev before
> > > devfs is mounted and if you look at root file systems
> > > mounted on other systems you well often find a /dev/null
> > > FILE that got created during the boot process from a >/dev/null
> > > before devfs was mounted.
> > >
> > 
> > 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.
> I would like to see some evidence for this actually occuring.
> 
> We mount devfs instance before root (yes), to get the device nodes
> available, so we can specify device name for root mount from loader.
> After mounting root we do a rearrangement to move devfs to /dev, which
> is somewhat tricky due to e.g. namecache.
> 
> I do not see how could anything in userspace even touch the underlying
> directory on rootfs of the /dev devfs mount.
> 
> OTOH, it is a usual problem with /tmp getting dirty, and the garbage
> hidden with tmpfs/md UFS mount over /tmp.

I consistantly find a /dev/null FILE on most systems when I take
a volume out of one machine and mount it as a non-boot volume.

I believe you can also see these in the underlying file system
on UFS with dump, or with zfs send.


-- 
Rod Grimes                                                 rgrimes at freebsd.org