initfamfs: bring back to life. Was also easy!

README.adoc

@@ -2617,6 +2617,8 @@ cat "$(./getvar run_dir)/run.sh"
 
 Instead, we used the QEMU `-initrd` option to point to the `.cpio` filesystem that Buildroot generated for us.
 
+Try removing that `-initrd` option to watch the kernel panic without rootfs at the end of boot.
+
 When using `.cpio`, there can be no filesystem persistency across boots, since all file operations happen in memory in a tmpfs:
 
 ....
@@ -2674,25 +2676,25 @@ Related: https://stackoverflow.com/questions/6405083/initrd-and-booting-the-linu
 
 TODO: broken when we started building the Linux manually with `./build-linux` instead of Buildroot. Was working before, see e.g. 56738a1c70e50bf7b6d5fbe02372c5d277a8286f.
 
-initramfs is just like <<initrd>>, but you also glue the image directly to the kernel image itself.
+initramfs is just like <<initrd>>, but you also glue the image directly to the kernel image itself using the kernel's build system.
-
-So the only argument that QEMU needs is the `-kernel`, no `-drive` not even `-initrd`! Pretty cool.
 
 Try it out with:
 
-....
-./build-buildroot --initramfs -l
-./run --initramfs
-....
-
-The `-l` (ell) should only be used the first time you move to / from a different root filesystem method (ext2 or cpio) to initramfs to overcome: https://stackoverflow.com/questions/49260466/why-when-i-change-br2-linux-kernel-custom-config-file-and-run-make-linux-reconfi
-
 ....
 ./build-buildroot --initramfs
+./build-linux --initramfs
 ./run --initramfs
 ....
 
-It is interesting to see how this increases the size of the kernel image if you do a:
+Notice how we had to rebuild the Linux kernel this time around as well after Buildroot, since in that build we will be gluing the CPIO to the kernel image.
+
+Now, once again, if we look at the QEMU run command generated, we see all that QEMU needs is the `-kernel` option, no `-drive` not even `-initrd`! Pretty cool:
+
+....
+cat "$(./getvar run_dir)/run.sh"
+....
+
+It is also interesting to observe how this increases the size of the kernel image if you do a:
 
 ....
 ls -lh "$(./getvar linux_image)"
@@ -2700,7 +2702,16 @@ ls -lh "$(./getvar linux_image)"
 
 before and after using initramfs, since the `.cpio` is now glued to the kernel image.
 
-In the background, it uses `BR2_TARGET_ROOTFS_INITRAMFS`, and this makes the kernel config option `CONFIG_INITRAMFS_SOURCE` point to the CPIO that will be embedded in the kernel image.
+Don't forget that to stop using initramfs, you must rebuild the kernel without `--initramfs`:
+
+....
+./build-linux
+./run
+....
+
+Also consider using <<linux-kernel-build-variants>> if you need to switch between initramfs and non initramfs often.
+
+Setting up initramfs is very easy: our scripts just set `CONFIG_INITRAMFS_SOURCE` to point to the CPIO path.
 
 http://nairobi-embedded.org/initramfs_tutorial.html shows a full manual setup.
 
@@ -5415,10 +5426,10 @@ Where the data comes from and how to modify it:
 
 In this repo, leaking host information, and to make builds more reproducible, we are setting:
 
-- user and date to dummy values
+- user and date to dummy values with `KBUILD_BUILD_USER` and `KBUILD_BUILD_TIMESTAMP`
-- hostname to the kernel git commit
+- hostname to the kernel git commit with `KBUILD_BUILD_HOST` and  `KBUILD_BUILD_VERSION`
 
-So the file contains something like:
+A sample result is:
 
 ....
 Linux version 4.19.0-dirty (lkmc@84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d) (gcc version 6.4.0 (Buildroot 2018.05-00002-gbc60382b8f)) #1 SMP Thu Jan 1 00:00:00 UTC 1970

build-buildroot

@@ -133,7 +133,7 @@ usually extra Buildroot targets.
             config_fragments = [
                 os.path.join(self.env['root_dir'], 'buildroot_config', 'default')
             ] + self.env['config_fragment']
-        if self.env['initrd']:
+        if self.env['initrd'] or self.env['initramfs']:
             configs.append('BR2_TARGET_ROOTFS_CPIO=y')
         # TODO Can't get rid of these for now with nice fragments on Buildroot:
         # http://stackoverflow.com/questions/44078245/is-it-possible-to-use-config-fragments-with-buildroots-config

build-linux

@@ -64,8 +64,6 @@ Run `make modules_install` after `make`.
 
     def build(self):
         build_dir = self.get_build_dir()
-        if self.env['initrd'] or self.env['initramfs']:
-            raise Exception('just trolling, --initrd and --initramfs are broken for now')
         os.makedirs(build_dir, exist_ok=True)
         tool = 'gcc'
         gcc = self.get_toolchain_tool(tool)
@@ -105,10 +103,12 @@ Run `make modules_install` after `make`.
             for i, config_fragment in enumerate(config_fragments):
                 config_fragments[i] = os.path.join(self.env['linux_config_dir'], config_fragment)
         config_fragments.extend(self.env['config_fragment'])
-        if self.env['config'] != []:
+        cli_configs = self.env['config']
+        if self.env['initramfs']:
+            cli_configs.append('CONFIG_INITRAMFS_SOURCE="{}"'.format(self.env['buildroot_cpio']))
+        if cli_configs:
             cli_config_fragment_path = os.path.join(build_dir, 'lkmc_cli_config_fragment')
-            cli_config_str = '\n'.join(self.env['config'])
+            self.sh.write_configs(cli_config_fragment_path, cli_configs, mode='w')
-            self.sh.write_string_to_file(cli_config_fragment_path, cli_config_str)
             config_fragments.append(cli_config_fragment_path)
         self.sh.cp(
             base_config_file,
@@ -136,6 +136,7 @@ Run `make modules_install` after `make`.
                     common_make_args +
                     self.sh.add_newlines(self.env['extra_make_args'])
                 ),
+                # https://github.com/cirosantilli/linux-kernel-module-cheat#proc-version
                 extra_env={
                     'KBUILD_BUILD_VERSION': '1',
                     'KBUILD_BUILD_TIMESTAMP': 'Thu Jan  1 00:00:00 UTC 1970',

common.py

@@ -255,14 +255,16 @@ Use the given directory as the Linux source tree.
 '''
         )
         self.add_argument(
-            '--initramfs', default=False,
+            '--initramfs',
+            default=False,
         )
         self.add_argument(
             '--initrd',
             default=False,
             help='''\
-Make Buildroot create a CPIO root filessytem, and make QEMU use it instead of
+For Buildroot: create a CPIO root filessytem.
-the default ext2.
+For QEMU use that CPUI root filesystem initrd instead of the default ext2.
+See: https://github.com/cirosantilli/linux-kernel-module-cheat#initrd
 '''
         )
 
@@ -477,6 +479,7 @@ Valid emulators: {}
         env['buildroot_images_dir'] = join(env['buildroot_build_dir'], 'images')
         env['buildroot_rootfs_raw_file'] = join(env['buildroot_images_dir'], 'rootfs.ext2')
         env['buildroot_qcow2_file'] = env['buildroot_rootfs_raw_file'] + '.qcow2'
+        env['buildroot_cpio'] = join(self.env['buildroot_images_dir'], 'rootfs.cpio')
         env['staging_dir'] = join(env['out_dir'], 'staging', env['arch'])
         env['buildroot_staging_dir'] = join(env['buildroot_build_dir'], 'staging')
         env['target_dir'] = join(env['buildroot_build_dir'], 'target')
@@ -601,6 +604,7 @@ Valid emulators: {}
         else:
             env['userland_quit_cmd'] = '/poweroff.out'
         env['quit_init'] = 'init={}'.format(env['userland_quit_cmd'])
+        self.env['ramfs'] = self.env['initrd'] or self.env['initramfs']
 
         # Kernel modules.
         env['kernel_modules_build_dir'] = join(env['kernel_modules_build_base_dir'], env['arch'])

gem5-bench-dhrystone

@@ -10,7 +10,7 @@ cmd="./run --arch '$arch' --emulator gem5 --eval-busybox '/gem5.sh'"
 
 # These cache sizes roughly match the ARM Cortex A75
 # https://en.wikipedia.org/wiki/ARM_Cortex-A75
-restore='-l 1 -- --cpu-type=HPI --restore-with-cpu=HPI --caches --l2cache --l1d_size=64kB --l1i_size=64kB --l2_size=256kB'
+restore='--gem5-restore 1 -- --cpu-type=HPI --restore-with-cpu=HPI --caches --l2cache --l1d_size=64kB --l1i_size=64kB --l2_size=256kB'
 
 # Generate a checkpoint after Linux boots, using the faster and less detailed CPU.
 # The boot takes a while, be patient young Padawan.

run

@@ -117,7 +117,7 @@ gem.op5 --debug-flags=Exec fs.py --cpu-type=HPI --caches
             '--kdb', default=False,
         )
         self.add_argument(
-            '-l', '--gem5-restore', type=int,
+            '--gem5-restore', type=int,
             help='''\
 Restore the nth most recently taken gem5 checkpoint according to directory
 timestamps.
@@ -231,12 +231,8 @@ Run QEMU with VNC instead of the default SDL. Connect to it with:
             vnc = ['-vnc', ':0', LF]
         else:
             vnc = []
-        if self.env['initrd'] or self.env['initramfs']:
-            ramfs = True
-        else:
-            ramfs = False
         if self.env['eval'] is not None:
-            if ramfs:
+            if self.env['ramfs']:
                 initarg = 'rdinit'
             else:
                 initarg = 'init'
@@ -504,9 +500,9 @@ Run QEMU with VNC instead of the default SDL. Connect to it with:
                 if not qemu_executable_prebuilt:
                     cmd.extend(qemu_user_and_system_options)
                 if self.env['initrd']:
-                    extra_emulator_args.extend(['-initrd', os.path.join(self.env['buildroot_images_dir'], 'rootfs.cpio')])
+                    extra_emulator_args.extend(['-initrd', self.env['buildroot_cpio'], LF])
                 rr = self.env['record'] or self.env['replay']
-                if ramfs:
+                if self.env['ramfs']:
                     # TODO why is this needed, and why any string works.
                     root = 'root=/dev/anything'
                 else:

shell_helpers.py

@@ -269,9 +269,9 @@ class ShellHelpers:
             else:
                 os.unlink(path)
 
-    def write_configs(self, config_path, configs, config_fragments=None):
+    def write_configs(self, config_path, configs, config_fragments=None, mode='a'):
         '''
-        Write extra KEY=val configs into the given config file.
+        Append extra KEY=val configs into the given config file.
         '''
         if config_fragments is None:
             config_fragments = []
@@ -283,7 +283,7 @@ class ShellHelpers:
                     with open(config_fragment, 'r') as config_fragment_file:
                         for line in config_fragment_file:
                             config_file.write(line)
-        self.write_string_to_file(config_path, '\n'.join(configs), mode='a')
+        self.write_string_to_file(config_path, '\n'.join(configs), mode=mode)
 
     def write_string_to_file(self, path, string, mode='w'):
         if mode == 'a':
@@ -292,5 +292,5 @@ class ShellHelpers:
             redirect = '>'
         self.print_cmd("cat << 'EOF' {} {}\n{}\nEOF".format(redirect, path, string))
         if not self.dry_run:
-            with open(path, 'a') as f:
+            with open(path, mode) as f:
                 f.write(string)