[TUHS] UNIX of choice these days?

Norman Wilson norman at oclsc.org
Mon Sep 25 22:07:16 AEST 2017


Larry McVoy:
> +1 on what Ron said.  I don't get the rationale for going back to ptrace.
> Anyone know what it is?  Is there a perf issue?

Kurt H Maier:

  The usual rationale presented is that someone can exhaust the fd table
  and then you can't get anything done.  Instead of fixing that problem,
  the popular approach is to add more syscalls, like with getrandom(2).

====

Funny that that rationale isn't extended to its logical
conclusion: get rid of open and creat.  Then nobody needs
to worry about running out of file descriptors ever!

I too am saddened to see such a retrograde step, but perhaps
I'm biased.  When I arrived in 1127, the kernel had /proc but
still had ptrace as well.  Why?  Because no one was brave enough
to wade into sdb and adb.

After a couple of years, I felt brave enough, so I did it.
Once the revised sdb and adb had propagated to all our systems,
I removed the syscall.  I celebrated by physically removing
ptrace(2) from the Eighth Edition manual in the UNIX room: the
manual entry comprised two facing pages, which I glued together.

I can sympathize with FreeBSD excuse someone cited elsewhere,
that nobody used the code so it should go--I'm always in favour
of improving programs by chopping sutff out--but I think the
decision here was backwards.  The proper answer would have been
to teach ps et al to use /proc, not to invent a new complex of
system calls.

I dislike how Linux has tossed information about processes and
other system-related data into the same namespace (and now that
there is /sys as well as /proc, I wonder whether it's time to
divorce them, or even to move /proc into /sys/proc), but the
general direction of moving things into the file system makes
sense.  I have some qualms about adding more and more code to
the kernel that just does string processing (making the kernel
bigger and more complicated, and widening the attack surface
for bad guys), though; maybe most of that stuff belongs not in
the OS proper but in a user-mode program that reads /dev/mem
and presents as a file system.

Norman Wilson
Toronto ON



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