Simplify parallel fuzzing

[remexre]

It's a bit of a pain to have to start multiple instances of cargo afl to parallelize; it'd be nice to have cargo afl be able to manage multiple instances itself.

[abonander]

The hardest part I think would be designing a terminal UI showing the overall fuzz progress and statistics; the master instance unfortunately only shows its own stats.

[dbrgn]

In case this is useful to others, I wrote this script, which launches multiple sessions in tmux:

#!/usr/bin/env bash
#
# Requirements:
#
# - nproc
# - tmux

set -euo pipefail

# Detect cores
ALL_CORES=$(nproc)
USED_CORES=$((ALL_CORES - 2))
if [[ "$USED_CORES" -lt 2 ]]; then
    echo "Error: USED_CORES < 2"
    exit 1
fi

# Usage
function print_usage() {
    echo "Usage: $0 [-j PROCS]"
    echo ""
    echo "Options:"
    echo "  -j PROCS    Number of parallel jobs to use (default: $USED_CORES)"
    echo "  -h,--help   Print this help and exit"
}

# Parse arguments
while [[ "$#" -gt 0 ]]; do
    case $1 in
        -j) USED_CORES=$2; shift ;;
        -h|--help) print_usage; exit 0 ;;
    esac
    shift
done
echo "Using $USED_CORES out of $ALL_CORES cores"

# Local variables
in_dir=in
sync_dir=sync_dir
tmux_window=afl

# Start main node
tmux new -d -s "afl01" -n $tmux_window "cargo afl fuzz -i $in_dir -o $sync_dir -M fuzzer01 target/debug/fuzz-target"
echo "Spawned main instance afl01"

# Start secondary instances
for i in $(seq -f "%02.0f" 2 "$USED_CORES"); do
    tmux new -d -s "afl$i" -n $tmux_window cargo afl fuzz -i $in_dir -o $sync_dir -S "fuzzer$i" target/debug/fuzz-target
    echo "Spawned secondary instance afl$i"
done

# Show status output
echo ""
echo "Tmux sessions:"
tmux ls | grep afl
echo ""
echo "Tmux cheatsheet (shell):"
echo "  Attach:"
echo "    tmux attach -t afl01"
echo "  Kill all sessions:"
echo "    tmux kill-server"
echo ""
echo "Tmux chatsheet (inside tmux):"
echo "  List sessions:"
echo "    Ctrl-b s"
echo "  Switch to next session:"
echo "    Ctrl-b )"
echo "  Switch to prev session:"
echo "    Ctrl-b ("
echo "  Detach:"
echo "    Ctrl-b d"

This works, but I'm missing some kind of "progress overview" over all parallel tasks (especially when using 30 cores in parallel), so a "native" solution would definitely be welcome. As a workaround, I use the session list (C-b s) and then cycle through the active sessions with up/down.