chcorefilter

[Roland McGrath <roland@xxxxxxxxxx>]

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.  Where should it live?  In the upstream
kernel's scripts/?  (Then noone would ever see it for sure.)  
In util-linux-ng?  Or what?  Someone want to take it off my hands?


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

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