chcorefilter

[Roland McGrath <roland@xxxxxxxxxx>]

Hi folks.  This is not a proper patch because I haven't done the polish
work for this and don't intend to bother.  But here it is just in case you
would like to take it up.

The /proc/PID/coredump_filter mechanism makes it easy to tweak the
per-process setting to control ELF core dump style details.  
This setting is per-process (per-mm) and inherited by children.

But as a user, the /proc interface is insane.  It prints a magical hex
value (without a leading 0x, to make it sneaky), which you'll be damn lucky
to figure out from reading Documentation/filesystems/proc.txt.  Then you
get to set it to another such magical value, which is in decimal unless you
add a leading 0x (cat /proc/x/coredump_filter > /proc/y/coredump_filter
does not copy the setting, go team).

I have kicking around this half-assed bash script that I don't care to
bother making really presentable.  I don't want to maintain or distribute
it or anything myself, and util-linux-ng seems like a good fit.  If you
think some other project should cover the need for this utility instead,
please point me to it.

The script itself is trivial, and not quite complete for real quality of
command line interface standards and so forth.  I think it serves at least
as adequate documentation of what a useful utility for this would do.  I
certainly won't mind if you want to do it a different way, give it a
different name and interface, etc.  I do think users would be well-served
by having some human-comprehensible procedure for fiddling these settings
from scripts and command lines.


Thanks,
Roland

#!/bin/bash
#
# Usage: chcorefilter - PID...		prints [pmfse]+ string for each PID
#        chcorefilter [pmfse]+ PID...	changes filter bits for each PID
#
# Each bit set says a flavor of mapping that should be included in core dumps.
# The setting for a process is inherited by its new children.
#
#	p	anonymous Private memory
#	m	anonymous shared Memory
#	f	private File mapping
#	s	Shared file mapping
#	e	ELF headers (first page of ELF-looking untouched file mapping)
#
# Default setting upstream is 'pm', Fedora >= 8 default is 'pme'.
# GDB < 6.7 will be confused by the core files from +e settings.
#
# A fancier command would take +e or -e to set/clear just some
# bits relative to the current setting.
#

get_filter()
{
  local pid=$1
  local f
  f=`cat /proc/$pid/coredump_filter` || exit
  ((f=0x$f))

  local s=''
  ((($f & 1) == 0)) || s="${s}p"
  ((($f & 2) == 0)) || s="${s}m"
  ((($f & 4) == 0)) || s="${s}f"
  ((($f & 8) == 0)) || s="${s}s"
  ((($f & 16) == 0)) || s="${s}e"

  filter_dec=$f
  filter_str=${s:-.}
}

set_filter()
{
  local pid=$1
  local val=$2
  printf "0x%x\n" $val > /proc/$pid/coredump_filter || exit
}

if [ $# -eq 0 ]; then
  exec sed '1d;/^#/!q' $0
fi

if [ "x$1" = x- ]; then
  shift
  for pid; do
    get_filter $pid
    if [ $# -gt 1 ]; then
      echo "${pid}: ${filter_str}"
    else
      echo "$filter_str"
    fi
  done
  exit 0
fi

arg="$1"
shift

case "$arg" in
-*) op='&=~'; arg=${arg#?} ;;
+*) op='|=' ; arg=${arg#?} ;;
.)  op='='  ; arg=${arg#?} ;;
*)  op='=' ;;
esac

val=0
until [ -z "$arg" ]; do
  case "$arg" in
    p*) ((val |= 1));;	# anonymous Private memory
    m*) ((val |= 2));;	# anonymous shared Memory
    f*) ((val |= 4));;	# private File mapping
    s*) ((val |= 8));;	# Shared file mapping
    e*) ((val |= 16));;	# ELF headers
    *) bogon; break ;;
  esac
  arg=${arg#?}
done

for pid; do
  get_filter $pid
  ((filter_dec $op $val))
  set_filter $pid $filter_dec
done