kdumpctl: Add kdumpctl estimate

Add a rough esitimation support, currently, following memory usage are
checked by this sub command:

- System RAM
- Kdump Initramfs size
- Kdump Kernel image size
- Kdump Kernel module size
- Kdump userspace user and other runtime allocated memory (currently
  simply using a fixed value: 64M)
- LUKS encryption memory usage

The output of kdumpctl estimate looks like this:
  # kdumpctl estimate
  Reserved crashkernel:    256M
  Recommanded crashkernel: 160M

  Kernel image size:   47M
  Kernel modules size: 12M
  Initramfs size:      19M
  Runtime reservation: 64M
  Large modules:
      xfs: 1892352
      nouveau: 2318336

And if the kdump target is encrypted:
  # kdumpctl estimate
  Encrypted kdump target requires extra memory, assuming using the keyslot with minimun memory requirement

  Reserved crashkernel:    256M
  Recommanded crashkernel: 655M

  Kernel image size:   47M
  Kernel modules size: 12M
  Initramfs size:      19M
  Runtime reservation: 64M
  LUKS required size:  512M
  Large modules:
      xfs: 1892352
      nouveau: 2318336
  WARNING: Current crashkernel size is lower than recommanded size 655M.

The "Recommanded" value is calculated based on memory usages mentioned
above, and will be adjusted accodingly to be no less than the value provided
by kdump_get_arch_recommend_size.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Pingfan Liu <piliu@redhat.com>

kdump-lib.sh

@@ -996,3 +996,74 @@ get_all_kdump_crypt_dev()
         [[ -n "$_crypt" ]] && echo $_crypt
     done
 }
+
+check_vmlinux()
+{
+    # Use readelf to check if it's a valid ELF
+    readelf -h $1 &>/dev/null || return 1
+}
+
+get_vmlinux_size()
+{
+    local size=0
+
+    while read _type _offset _virtaddr _physaddr _fsize _msize _flg _aln; do
+        size=$(( $size + $_msize ))
+    done <<< $(readelf -l -W $1 | grep "^  LOAD" 2>/dev/stderr)
+
+    echo $size
+}
+
+try_decompress()
+{
+    # The obscure use of the "tr" filter is to work around older versions of
+    # "grep" that report the byte offset of the line instead of the pattern.
+
+    # Try to find the header ($1) and decompress from here
+    for pos in `tr "$1\n$2" "\n$2=" < "$4" | grep -abo "^$2"`
+    do
+        if ! type -P $3 > /dev/null; then
+            ddebug "Signiature detected but '$3' is missing, skip this decompressor"
+            break
+        fi
+
+        pos=${pos%%:*}
+        tail -c+$pos "$img" | $3 > $5 2> /dev/null
+        if check_vmlinux $5; then
+            ddebug "Kernel is extracted with '$3'"
+            return 0
+        fi
+    done
+
+    return 1
+}
+
+# Borrowed from linux/scripts/extract-vmlinux
+get_kernel_size()
+{
+    # Prepare temp files:
+    local img=$1 tmp=$(mktemp /tmp/vmlinux-XXX)
+    trap "rm -f $tmp" 0
+
+    # Try to check if it's a vmlinux already
+    check_vmlinux $img && get_vmlinux_size $img && return 0
+
+    # That didn't work, so retry after decompression.
+    try_decompress '\037\213\010' xy    gunzip    $img $tmp || \
+    try_decompress '\3757zXZ\000' abcde unxz      $img $tmp || \
+    try_decompress 'BZh'          xy    bunzip2   $img $tmp || \
+    try_decompress '\135\0\0\0'   xxx   unlzma    $img $tmp || \
+    try_decompress '\211\114\132' xy    'lzop -d' $img $tmp || \
+    try_decompress '\002!L\030'   xxx   'lz4 -d'  $img $tmp || \
+    try_decompress '(\265/\375'   xxx   unzstd    $img $tmp
+
+    # Finally check for uncompressed images or objects:
+    [[ $? -eq 0 ]] && get_vmlinux_size $tmp && return 0
+
+    # Fallback to use iomem
+    local _size=0
+    for _seg in $(cat /proc/iomem  | grep -E "Kernel (code|rodata|data|bss)" | cut -d ":" -f 1); do
+	    _size=$(( $_size + 0x${_seg#*-} - 0x${_seg%-*} ))
+    done
+    echo $_size
+}

kdumpctl

@@ -1249,6 +1249,97 @@ rebuild() {
 	return $?
 }
 
+do_estimate() {
+	local kdump_mods
+	local -A large_mods
+	local baseline
+	local kernel_size mod_size initrd_size baseline_size runtime_size reserved_size estimated_size recommanded_size
+	local size_mb=$(( 1024 * 1024 ))
+
+	setup_initrd
+	if [ ! -f "$TARGET_INITRD" ]; then
+		derror "kdumpctl estimate: kdump initramfs is not built yet."
+		exit 1
+	fi
+
+	kdump_mods="$(lsinitrd "$TARGET_INITRD" -f /usr/lib/dracut/hostonly-kernel-modules.txt | tr '\n' ' ')"
+	baseline=$(kdump_get_arch_recommend_size)
+	if [[ "${baseline: -1}" == "M" ]]; then
+		baseline=${baseline%M}
+	elif [[ "${baseline: -1}" == "G" ]]; then
+		baseline=$(( ${baseline%G} * 1024 ))
+	elif [[ "${baseline: -1}" == "T" ]]; then
+		baseline=$(( ${baseline%Y} * 1048576 ))
+	fi
+
+	# The default value when using crashkernel=auto
+	baseline_size=$((baseline * size_mb))
+	# Current reserved crashkernel size
+	reserved_size=$(cat /sys/kernel/kexec_crash_size)
+	# A pre-estimated value for userspace usage and kernel
+	# runtime allocation, 64M should good for most cases
+	runtime_size=$((64 * size_mb))
+	# Kernel image size
+	kernel_size=$(get_kernel_size "$KDUMP_KERNEL")
+	# Kdump initramfs size
+	initrd_size=$(du -b "$TARGET_INITRD" | awk '{print $1}')
+	# Kernel modules static size after loaded
+	mod_size=0
+	while read -r _name _size _; do
+		if [[ ! " $kdump_mods " == *" $_name "* ]]; then
+			continue
+		fi
+		mod_size=$((mod_size + _size))
+
+		# Mark module with static size larger than 2M as large module
+		if [[ $((_size / size_mb)) -ge 1 ]]; then
+			large_mods[$_name]=$_size
+		fi
+	done <<< "$(< /proc/modules)"
+
+	# Extra memory usage required for LUKS2 decryption
+	crypt_size=0
+	for _dev in $(get_all_kdump_crypt_dev); do
+		_crypt_info=$(cryptsetup luksDump "/dev/block/$_dev")
+		[[ $(echo "$_crypt_info" | sed -n "s/^Version:\s*\(.*\)/\1/p" ) == "2" ]] || continue
+		for _mem in $(echo "$_crypt_info" | sed -n "s/\sMemory:\s*\(.*\)/\1/p" | sort -n ); do
+			crypt_size=$((crypt_size + _mem * 1024))
+			break
+		done
+	done
+	[[ $crypt_size -ne 0 ]] && echo -e "Encrypted kdump target requires extra memory, assuming using the keyslot with minimun memory requirement\n"
+
+	estimated_size=$((kernel_size + mod_size + initrd_size + runtime_size + crypt_size))
+	if [[ $baseline_size -gt $estimated_size ]]; then
+		recommanded_size=$baseline_size
+	else
+		recommanded_size=$estimated_size
+	fi
+
+	echo "Reserved crashkernel:    $((reserved_size / size_mb))M"
+	echo "Recommanded crashkernel: $((recommanded_size / size_mb))M"
+	echo
+	echo "Kernel image size:   $((kernel_size / size_mb))M"
+	echo "Kernel modules size: $((mod_size / size_mb))M"
+	echo "Initramfs size:      $((initrd_size / size_mb))M"
+	echo "Runtime reservation: $((runtime_size / size_mb))M"
+	[[ $crypt_size -ne 0 ]] && \
+	echo "LUKS required size:  $((crypt_size / size_mb))M"
+	echo -n "Large modules:"
+	if [[ "${#large_mods[@]}" -eq 0 ]]; then
+		echo " <none>"
+	else
+		echo ""
+		for _mod in "${!large_mods[@]}"; do
+			echo "    $_mod: ${large_mods[$_mod]}"
+		done
+	fi
+
+	if [[ $reserved_size -le $recommanded_size ]]; then
+		echo "WARNING: Current crashkernel size is lower than recommanded size $((recommanded_size / size_mb))M."
+	fi
+}
+
 if [ ! -f "$KDUMP_CONFIG_FILE" ]; then
 	derror "Error: No kdump config file found!"
 	exit 1
@@ -1304,8 +1395,11 @@ main ()
 	  showmem)
 		show_reserved_mem
 		;;
+	  estimate)
+		do_estimate
+		;;
 	  *)
-		dinfo $"Usage: $0 {start|stop|status|restart|reload|rebuild|propagate|showmem}"
+		dinfo $"Usage: $0 {estimate|start|stop|status|restart|reload|rebuild|propagate|showmem}"
 		exit 1
 	esac
 }

kdumpctl.8

@@ -44,6 +44,11 @@ impossible to use password authentication during kdump.
 .TP
 .I showmem
 Prints the size of reserved memory for crash kernel in megabytes.
+.TP
+.I estimate
+Estimate a suitable crashkernel value for current machine. This is a
+best-effort estimate. It will print a recommanded crashkernel value
+based on current kdump setup, and list some details of memory usage.
 
 .SH "SEE ALSO"
 .BR kdump.conf (5),