Add tests and documentation for Pdeathsig behavior in rootlesskit

Signed-off-by: fahed dorgaa <fahed.dorgaa@gmail.com>

Author: fahedouch

hack/integration-pdeathsig.sh

@@ -0,0 +1,100 @@
+#!/bin/bash
+# Test script to verify Pdeathsig behavior using rootlesskit itself
+# This script:
+# 1. Uses rootlesskit to spawn a long-running process
+# 2. Kills the rootlesskit parent process
+# 3. Verifies that the child process is killed as expected
+
+source $(realpath $(dirname $0))/common.inc.sh
+
+INFO "Starting Pdeathsig test using rootlesskit..."
+
+# Create a temporary directory for test artifacts
+TEMP_DIR=$(mktemp -d)
+INFO "Created temporary directory: $TEMP_DIR"
+
+# Create a marker file that will be touched by the child process if it's still alive
+MARKER_FILE="$TEMP_DIR/child_still_alive"
+
+# Create a script that will be executed by rootlesskit
+CHILD_SCRIPT="$TEMP_DIR/child_script.sh"
+cat > "$CHILD_SCRIPT" << 'EOF'
+#!/bin/bash
+echo "Child process started with PID: $$"
+echo "Parent PID: $PPID"
+
+# Register a trap to handle signals
+trap 'echo "Child received signal, exiting"; exit 1' TERM INT
+
+# Run for 30 seconds, checking if parent is still alive
+for i in {1..30}; do
+    echo "Child still running (iteration $i)..."
+
+    # Check if parent has changed (died)
+    CURRENT_PPID=$(ps -o ppid= -p $$)
+    if [ "$CURRENT_PPID" != "$PPID" ]; then
+        echo "Parent changed from $PPID to $CURRENT_PPID"
+        if [ "$CURRENT_PPID" = "1" ]; then
+            echo "Parent is now init (PID 1), parent has died"
+            echo "Child should be killed by Pdeathsig, but if you see this message, it wasn't"
+            touch MARKER_FILE_PLACEHOLDER
+            exit 1
+        fi
+    fi
+
+    sleep 1
+done
+
+# If we reach here, the child wasn't killed
+echo "Child completed normally (this shouldn't happen if Pdeathsig is working)"
+touch MARKER_FILE_PLACEHOLDER
+EOF
+
+# Replace the placeholder with the actual marker file path
+sed -i "s|MARKER_FILE_PLACEHOLDER|$MARKER_FILE|g" "$CHILD_SCRIPT"
+chmod +x "$CHILD_SCRIPT"
+
+# Start rootlesskit with the child script
+INFO "Starting rootlesskit..."
+$ROOTLESSKIT "$CHILD_SCRIPT" &
+ROOTLESSKIT_PID=$!
+INFO "Rootlesskit started with PID: $ROOTLESSKIT_PID"
+
+# Wait a moment for the child to start
+sleep 2
+
+# Find the child process
+CHILD_PID=$(pgrep -P $ROOTLESSKIT_PID)
+if [ -z "$CHILD_PID" ]; then
+    ERROR "Failed to find child process"
+    exit 1
+fi
+INFO "Found child process with PID: $CHILD_PID"
+
+# Kill the rootlesskit process
+INFO "Killing rootlesskit process (PID: $ROOTLESSKIT_PID)..."
+kill -9 $ROOTLESSKIT_PID
+
+# Wait a moment for the child to be killed
+sleep 2
+
+# Check if the child process is still running
+if ps -p $CHILD_PID > /dev/null; then
+    ERROR "FAIL: Child process (PID: $CHILD_PID) is still running after parent was killed"
+    kill -9 $CHILD_PID  # Clean up
+    exit 1
+else
+    INFO "PASS: Child process (PID: $CHILD_PID) was killed as expected"
+fi
+
+# Check if the marker file exists
+if [ -f "$MARKER_FILE" ]; then
+    ERROR "FAIL: Marker file exists, which means the child process wasn't killed by Pdeathsig"
+    exit 1
+else
+    INFO "PASS: Marker file doesn't exist, which means the child process was killed by Pdeathsig"
+fi
+
+INFO "Test completed successfully!"
+rm -rf "$TEMP_DIR"
+exit 0