Re: [woody-discussion] cramfs - compressed rom fs
On Fri, Mar 31, 2000 at 03:40:07PM +0000, bug1 wrote:
> Ive just been playing with cramfs, which is a compressed rom fs included
> in the 2.3.x series.
>
> I made a cramfs image with the same contents as the current root.img,
> cramfs doesnt support hard links, so i converted them to soft links.
>
> root.img (zipped) is 963018 Bytes
> cramfs img is 1081344 Bytes
That may be on i386, however the test I did for sparc's root.bin ended up
being 1.5 megs. Too large for a floppy. Perhaps with devfs, this wouldn't
be so bad though since all of /dev would be gone from the actual image.
> I tried testing it, i dd'ed the image to a floppy and copyed a 2.3
> kernel with compressed rom fs support built into the kernel to the
> rescue disk.
>
> The rescuedisk booted, loaded the root img, but then after init started
> busybox gave an error saying i didnt have enough memory, i have 64MB
> which is plenty.
>
> Maybe busybox doesnt like read only filesystems, i dont know. Ive heard
> devfs is really needed to use a rom rootfs, ihavent played with devfs
> yet....
Acutall busbox has no problems with read-only filesystems. The sparc
CDROM's will be booting from an iso9660 root filesystem. This works
perfectly well (although I do have to mount a ramdisk for /tmp and point
stuff in /var to /tmp).
> Compressed root romfs should be technically possible, wether its worth
> it is another question.
>
>
> ADVANTAGES to root cramfs
>
> 1) lowmem machines could use a floppy as a rootfs instead of a ramdisk
Probably the most important reason.
> 2) a rom root fs would provide a more generic base for booting from
> other mediums e.g. CD's
I've been working on making dboostrap work with ro file systems. Hopefully
this will make future use of this more easy.
>
> DISADVANTAGES to root cramfs
>
> 1) Size, takes up over 10% more space from the rootfs medium.
>
> 2) Speed, ramdisk based rootfs will always be more responsive than
> rootfs on disk/floppy or anywhere else.
>
>
> Im not sure wether cramfs is a good idea, but seems as i checked it out
> i thought i may as well report on my experience.
You went a little more in depth than I did. Since I couldn't fit the
root.bin on the floppy, I didn't try to boot it. Maybe I can check back
with this using devfs and remove the devices from the fs, but that would
require also using devfsd or making lots of changes in dbootstrap/busybox
to support the different device layout in devfs.
--
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/ Ben Collins -- ...on that fantastic voyage... -- Debian GNU/Linux \
` bcollins@debian.org -- bcollins@openldap.org -- bmc@visi.net '
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