#!/bin/bash
#
# fdswap
#
if [ "$2" = "" ]; then 
	echo "
    Usage: $0 /path/to/oldfile /path/to/newfile [pids]
    Example: $0 /var/log/daemon.log /var/log/newvolume/daemon.log 1234
    Example: $0 /dev/pts/53 /dev/null 2345"; exit 0
fi

if gdb --version > /dev/null 2>&1; then true
else echo "Unable to find gdb."; exit 1
fi

src="$1"; dst="$2"; shift; shift 
pids=$* 

for pid in ${pids:=$( /sbin/fuser $src | cut -d ':' -f 2 )}; 
do
    echo "src=$src, dst=$dst"
    echo "$src has $pid using it" 
    cmd=$(mktemp)
    { 
        echo "attach $pid" 
        echo 'call (int)open("'$dst'", 66, 0666)'
        for ufd in $(LANG=C ls -l /proc/$pid/fd | \
        grep "$src"\$ | awk ' { print $9; } '); 
        do echo 'call (int)dup2($1,'"$ufd"')'; done 
        echo 'call (int)close($1)'
        echo 'detach'; echo 'quit' 
        sleep 5
    } | tee /dev/tty >$cmd
    gdb -x $cmd
done