Support swap files in qemu or bare-metal mode

This can help alleviate memory pressure when bootstrapping
with high core counts.

rootfs.py

@@ -12,6 +12,7 @@ you can run bootstap inside chroot.
 # SPDX-FileCopyrightText: 2021 Bastian Bittorf <bb@npl.de>
 # SPDX-FileCopyrightText: 2021 Melg Eight <public.melg8@gmail.com>
 # SPDX-FileCopyrightText: 2021-23 fosslinux <fosslinux@aussies.space>
+# SPDX-FileCopyrightText: 2023-24 Gábor Stefanik <netrolller.3d@gmail.com>
 
 import argparse
 import os
@@ -31,6 +32,7 @@ def create_configuration_file(args):
         config.write(f"CHROOT={args.chroot or args.bwrap}\n")
         config.write(f"UPDATE_CHECKSUMS={args.update_checksums}\n")
         config.write(f"JOBS={args.cores}\n")
+        config.write(f"SWAP_SIZE={args.swap}\n")
         config.write(f"INTERNAL_CI={args.internal_ci or False}\n")
         config.write(f"BARE_METAL={args.bare_metal}\n")
         if (args.bare_metal or args.qemu) and not args.kernel:
@@ -44,7 +46,7 @@ def create_configuration_file(args):
             config.write("KERNEL_BOOTSTRAP=False\n")
         config.write(f"BUILD_KERNELS={args.update_checksums or args.build_kernels}\n")
 
-# pylint: disable=too-many-statements
+# pylint: disable=too-many-statements,too-many-branches
 def main():
     """
     A few command line arguments to customize bootstrap.
@@ -86,6 +88,8 @@ def main():
     parser.add_argument("--early-preseed",
                         help="Skip early stages of live-bootstrap.", nargs=None)
     parser.add_argument("--internal-ci", help="INTERNAL for github CI")
+    parser.add_argument("-s", "--swap", help="Swap space to allocate in Linux",
+                        default=0)
 
     # QEMU arguments
     parser.add_argument("-q", "--qemu", help="Use QEMU",
@@ -143,6 +147,13 @@ def main():
     else:
         args.target_size = 0
 
+    # Swap file size validation
+    if args.qemu or args.bare_metal:
+        args.swap = (int(str(args.swap).rstrip('gGmM')) *
+            (1024 if str(args.swap).lower().endswith('g') else 1))
+    else:
+        args.swap = 0
+
     # bootstrap.cfg
     try:
         os.remove(os.path.join('steps', 'bootstrap.cfg'))

steps/improve/swap.sh

@@ -0,0 +1,19 @@
+
+#!/bin/sh
+#
+# SPDX-FileCopyrightText: 2024 Gábor Stefanik <netrolller.3d@gmail.com>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# Set up swap
+
+. /steps/bootstrap.cfg
+. /steps/env
+
+if ! test -f /swapfile
+then
+    echo "Making swap..."
+    dd if=/dev/zero of=/swapfile bs=1M count=${SWAP_SIZE}
+    mkswap /swapfile
+fi
+swapon /swapfile

steps/manifest

@@ -119,6 +119,7 @@ build: linux-4.9.10 ( BUILD_LINUX == True )
 jump: break ( INTERNAL_CI == pass1 )
 jump: linux ( CHROOT == False )
 improve: finalize_fhs
+improve: swap ( SWAP_SIZE != 0 )
 build: musl-1.2.4
 build: curl-8.5.0
 improve: populate_device_nodes