Re: [gentoo-catalyst] How is initrd built?

[Eric Edgar]

You technically cannot extract the cpio archive as far as I can tell
because it really is multiple cpio archives concatenated together.

the kernel takes each one and overlays them ontop of eachother.
this makes it easy to create a new cpio archive and cat it to the end of
the existing archive to override any file.  It does make the initramfs
file itself bigger, but shouldnt take any more ram.

There is an --initramfs-overlay option that will allow you to do this
automatically as it points to a directory and copies its structure into
the initramfs.

cd ${INITRAMFS_OVERLAY}
find . -print | cpio --quiet -o -H newc | gzip -9 > ${CACHE_DIR}/cpio/initramfs-overlay.cpio.gz
cat old-oldinitramfs.cpio.gz initramfs-overlay.cpio.gz 	> new-initramfs.cpio.gz	

We did it this way because its easier to add or subtract components from
the initramfs. because udev is its own cpio file, busybox is its own
cpio file etc.  It would work as well if everything was one big cpio,
but then genkernel would be much slower as it has to do a lot more
copy operations.

Dont feel dumb.

On 10:35 Thu 07 Jul     , Paul Smith wrote:
> %% Chris Gianelloni <wolf31o2@g.o> writes:
>
>   cg> On Thu, 2005-07-07 at 09:50 -0400, Paul Smith wrote:
>   >> In the new version, the initrd doesn't appear to be an ext2 filesystem
>   >> anymore... it's some kind of compressed cpio file?!?!  Anyway, that's
>   >> what "file" tells me.
>
>   cg> It is an initramfs image.  You can work with it just like any
>   cg> other cpio archive.
>
> Well, yeah, I tried to do that, but it doesn't work.  What am I doing
> wrong (I haven't used cpio for years...)
>
> I unpack the tarball and then:
>
>   # gzcat isolinux/gentoo.igz | cpio -tv
>   drwxr-xr-x  11 root     root            0 Jul  6 20:09 .
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 dev
>   crw-rw----   1 root     root       5,   1 Jul  6 20:09 dev/console
>   crw-rw----   1 root     root       1,   3 Jul  6 20:09 dev/null
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 bin
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 etc
>   -rw-r--r--   1 root     root           93 Jul  6 20:09 etc/fstab
>   drwxr-xr-x   4 root     root            0 Jul  6 20:09 usr
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 usr/bin
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 usr/sbin
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 proc
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 temp
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 sys
>   drwxr-xr-x   3 root     root            0 Jul  6 20:09 var
>   drwxr-xr-x   3 root     root            0 Jul  6 20:09 var/lock
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 var/lock/dmraid
>   drwxr-xr-x   2 root     root            0 Jul  6 20:09 sbin
>
> Where's everything else?  If I actually extract the archive I get the
> same results: just this small directory skeleton and no actual contents
> other than the ones in bin.
>
> The file, of course, is huge and the system does boot properly so it's
> all in there somewhere, but...???
>
>
> I feel dumb :-/.
>
> --
> -------------------------------------------------------------------------------
>  Paul D. Smith <psmith@××××××.com>           HASMAT--HA Software Mthds & Tools
>  "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
> -------------------------------------------------------------------------------
>    These are my opinions---Nortel Networks takes no responsibility for them.
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