From: Olaf Hering <olh@suse.de>
initramfs can not be used in current 2.6 kernels, the files will never be
executed because prepare_namespace doesn't care about them. The only way to
workaround that limitation is a root=0:0 cmdline option to force rootfs as
root filesystem. This will break further booting because rootfs is not the
final root filesystem.
This patch checks for the presence of /init which comes from the cpio archive
(and thats the only way to store files into the rootfs). This binary/script
has to do all the work of prepare_namespace().
---
25-akpm/Documentation/early-userspace/README | 26 ++++++++++++++++++++++++++
25-akpm/init/main.c | 7 +++++++
2 files changed, 33 insertions(+)
diff -puN Documentation/early-userspace/README~initramfs-search-for-init-orig Documentation/early-userspace/README
--- 25/Documentation/early-userspace/README~initramfs-search-for-init-orig 2004-03-22 00:38:02.064936960 -0800
+++ 25-akpm/Documentation/early-userspace/README 2004-03-22 00:38:02.067936504 -0800
@@ -71,5 +71,31 @@ custom initramfs images that meet your n
For questions and help, you can sign up for the early userspace
mailing list at http://www.zytor.com/mailman/listinfo/klibc
+How does it work?
+=================
+
+The kernel has currently 3 ways to mount the root filesystem:
+
+a) all required device and filesystem drivers compiled into the kernel, no
+ initrd. init/main.c:init() will call prepare_namespace() to mount the
+ final root filesystem, based on the root= option and optional init= to run
+ some other init binary than listed at the end of init/main.c:init().
+
+b) some device and filesystem drivers built as modules and stored in an
+ initrd. The initrd must contain a binary '/linuxrc' which is supposed to
+ load these driver modules. It is also possible to mount the final root
+ filesystem via linuxrc and use the pivot_root syscall. The initrd is
+ mounted and executed via prepare_namespace().
+
+c) using initramfs. The call to prepare_namespace() must be skipped.
+ This means that a binary must do all the work. Said binary can be stored
+ into initramfs either via modifying usr/gen_init_cpio.c or via the new
+ initrd format, an cpio archive. It must be called "/init". This binary
+ is responsible to do all the things prepare_namespace() would do.
+
+ To remain backwards compatibility, the /init binary will only run if it
+ comes via an initramfs cpio archive. If this is not the case,
+ init/main.c:init() will run prepare_namespace() to mount the final root
+ and exec one of the predefined init binaries.
Bryan O'Sullivan <bos@serpentine.com>
diff -puN init/main.c~initramfs-search-for-init-orig init/main.c
--- 25/init/main.c~initramfs-search-for-init-orig 2004-03-22 00:38:02.065936808 -0800
+++ 25-akpm/init/main.c 2004-03-22 00:38:02.068936352 -0800
@@ -604,6 +604,13 @@ static int init(void * unused)
smp_init();
do_basic_setup();
+ /*
+ * check if there is an early userspace init, if yes
+ * let it do all the work
+ */
+ if (sys_access("/init", 0) == 0)
+ execute_command = "/init";
+ else
prepare_namespace();
/*
_