proc: add proc_mark_important server code

This is based on a fragment of Guillem Jovers patch presented here:

http://lists.gnu.org/archive/html/bug-hurd/2006-02/msg00081.html

It has been refreshed, updated and the copyright year is adjusted
properly. It has been complemented with the necessary features to
address the issues the original patch set out to address, namely
that killall5 freezes the proc translator before it tries to walk
over /proc/*/stat to decide which process to kill. Prior to this
patch (and the one marking the procfs server as important
process), killall5 would deadlock trying to walk over the proc
file system.

Ironically it would not have killed any process later on even if
it had the chance, since two values obtained from /proc/*/stat
are currently hardcoded to zero in our procfs. Patches addressing
the problem as a whole are prepared and will be sent as a follow
up.

* proc/proc.h (struct proc): Add p_important field.
* proc/pgrp.c (S_proc_getpgrppids): Exclude important system processes.
(S_proc_mark_important): New function.
* proc/mgt.c (create_startup_proc): Mark init as important.

1 files changed, 1 insertions, 0 deletions

diff --git a/proc/proc.h b/proc/proc.h
index b7a95662..ed47cccb 100644
--- a/proc/proc.h
+++ b/proc/proc.h
@@ -84,6 +84,7 @@ struct proc
   unsigned int p_noowner:1;	/* has no owner known */
   unsigned int p_loginleader:1;	/* leader of login collection */
   unsigned int p_dead:1;	/* process is dead */
+  unsigned int p_important:1;	/* has called proc_mark_important */
 };
 
 typedef struct proc *pstruct_t;