Example of ARM based linux board using initramfs and serial console

Thomas Charron twaffle at gmail.com
Fri Jul 11 13:27:12 EDT 2008


On 7/11/08, Ben Scott <dragonhawk at gmail.com> wrote:
> On Fri, Jul 11, 2008 at 11:53 AM, Thomas Charron <twaffle at gmail.com> wrote:
> >  There IS something that I can't recall the exact specifics of, but
> > it's along the lines of a 'magic identifier' in the filesystem that
> > says it can be a root FS by the kernel.
>  We're still talking Linux, right?
>  To the best of my knowledge, there is no such thing.  Any filesystem
> can be mounted as a root filesystem.  There's no magic in the
> filesystem.  (The kernel will panic if it then cannot find an initial
> program to start, but it will still mount the filesystem first.)
>  You may be thinking of the "rdev" field in the kernel boot image
> file.  It gives major and minor numbers for the default root device,
> which are used if you don't specify a "root=" argument on the kernel
> command line.

  I was talking specifically about an initramfs, which specifically
uses cpio.  initramfs.c checks for a magic flag in the header which
tells the kernel this is indeed a cpio compressed filesystem,
specifically for mounting as the initial root filesystem by the
kernel.  Sorry I wasn't more specific when I said 'filesystem',
perhaps I should have clarified with 'initramfs filesystem'.

-- 
-- Thomas


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