On Sat, Dec 01, 2007 at 09:22:28PM -0500, Robert P. J. Day wrote:
>
> just perusing the simple code in init/noinitramfs.c, which is
> what's invoked if you choose not to build in initrd support:
No, that's invoked when you choose not to build initramfs. IOW: it is
used when you build with initrd.
> static int __init default_rootfs(void)
> {
> int err;
>
> err = sys_mkdir("/dev", 0755);
> if (err < 0)
> goto out;
>
> err = sys_mknod((const char __user *) "/dev/console",
> S_IFCHR | S_IRUSR | S_IWUSR,
> new_encode_dev(MKDEV(5, 1)));
> if (err < 0)
> goto out;
>
> err = sys_mkdir("/root", 0700);
> if (err < 0)
> goto out;
>
> return 0;
> ...
>
> so, if you choose not to select initrd support, then the above trivial
> initial root filesystem better be everything you need to completely
> finish the boot process, right? i just want to make sure i'm not
> overlooking anything subtle.
No, when you don't use initrd, you get initramfs. The trivial initramfs
contains the same what the above code has, but in a packed cpio
archive. If you choose to use initrd, you don't get that packed cpio
archive, so the above code makes a simple root filesystem on which the
initrd image is mounted.
The difference between initrd and initramfs is that initrd contains a
filesystem image that's being put in a ramdisk and initramfs contains a
cpio archive that's put into the page cache (using ramfs/tmpfs). The
advantage of initramfs is that it doesn't need any particular
filesystem compiled into the kernel (i.e.: everything can be modular)
and that the final filesystem only occupies exactly enough space (no
wasted empty space in the ramdisk).
Erik
--
They're all fools. Don't worry. Darwin may be slow, but he'll
eventually get them. -- Matthew Lammers in alt.sysadmin.recovery
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