lxd-agent: Add validation script for RSS calculation

Add a validation script for RSS calculation that:

- Compares RSS calculation with free command output

- Uses awk with proper regex anchors for accurate parsing

- Provides detailed calculation breakdown for debugging

- Validates results are within 5% of standard tools

Co-authored-by: Simon Deziel <simon.deziel@canonical.com>
Signed-off-by: MrMartyK <martykareem@outlook.com>

lxd-agent/tests/test_rss_calculation.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+set -eu
+
+echo "=== RSS Calculation Validation Test ==="
+
+# Run free command to get baseline
+FREE_USED=$(free | awk '/^Mem:/ {print $3}')
+echo "Used memory from free command: $FREE_USED kB"
+
+# Get meminfo values
+MEM_TOTAL=$(awk '/^MemTotal:/ {print $2}' /proc/meminfo)
+MEM_FREE=$(awk '/^MemFree:/ {print $2}' /proc/meminfo)
+BUFFERS=$(awk '/^Buffers:/ {print $2}' /proc/meminfo)
+CACHED=$(awk '/^Cached:/ {print $2}' /proc/meminfo)
+SHMEM=$(awk '/^Shmem:/ {print $2}' /proc/meminfo)
+
+# Calculate RSS using our formula
+RSS=$((MEM_TOTAL - (MEM_FREE + BUFFERS + CACHED - SHMEM)))
+echo "RSS from our calculation: $RSS kB"
+
+# Display all values for debugging
+echo
+echo "Values from /proc/meminfo:"
+echo "  MemTotal:  $MEM_TOTAL kB"
+echo "  MemFree:   $MEM_FREE kB"
+echo "  Buffers:   $BUFFERS kB"
+echo "  Cached:    $CACHED kB"
+echo "  Shmem:     $SHMEM kB"
+echo "Formula: MemTotal - (MemFree + Buffers + Cached - Shmem)"
+echo "       = $MEM_TOTAL - ($MEM_FREE + $BUFFERS + $CACHED - $SHMEM)"
+echo "       = $MEM_TOTAL - $((MEM_FREE + BUFFERS + CACHED - SHMEM))"
+echo "       = $RSS kB"
+echo
+
+# Calculate difference percentage using shell math
+DIFF_RAW=$((RSS - FREE_USED))
+# Calculate percentage difference: (RSS - FREE_USED) / FREE_USED * 100
+DIFF_PCT=$(awk "BEGIN {print ($DIFF_RAW / $FREE_USED) * 100}")
+# Get absolute value of percentage difference for comparison
+ABS_DIFF_PCT=$(awk "BEGIN {print ($DIFF_PCT < 0) ? -$DIFF_PCT : $DIFF_PCT}")
+
+echo "Difference: $DIFF_RAW kB ($DIFF_PCT%)"
+echo "Absolute difference: $(printf "%.2f" "$ABS_DIFF_PCT")%"
+
+# Test passes if difference is less than 5%
+# Use awk to compare float values since bash can only handle integers
+if (( $(awk "BEGIN {print ($ABS_DIFF_PCT < 5.0) ? 1 : 0}") )); then
+    echo "✅ Test PASSED - difference within 5%"
+    exit 0
+else
+    echo "❌ Test FAILED - difference exceeds 5%"
+    exit 1
+fi