[uClibc] Buildroot & inittar patch

Thomas Cameron tom at drdabbles.us
Tue Dec 14 17:09:46 UTC 2004

> when I read that message in the linux-kernel ml, I thought of 
> the same... but 
> what do you gain with it? is there a real overhead spared 
> with tarfs filesystem 
> that you waste with gzipped ext2fs?

Simplicity, for one. All you do is feed a .tar.gz to the kernel, and it will
create a tmpfs filesystem for the initial filesystem. For me, this means I
can have a read-write filesystem that is limited in size only by memory
constraints or those I manually implement.

Another note of interest, which also answers half of your next question, is
that tmpfs is read-write, while images based on cramfs and squashfs. This
means any changes to the filesystem done by a user can cimply be tarred up,
and saved over the original inittar file. Again, this is convenient for
simplicity's sake, You no longer have to package such tools as genext2fs, or
any of the others.

> In the same subject what are the pros and cons of using these 
> filesystems in the 
> initrds:
> . gzipped ext2fs
> . cramfs
> . squashfs
> . tarfs
> What stops one from using any other filesystem? overhead?

Overhead is one issue, yes. For instance, if you create a root image with an
ext2 filesystem and an exact duplicate based on the minix filesystem you
will notice that the minix image is smaller. It's structures are smaller,
and it has fewer features than ext2.

With regard to cramfs, squashfs, and a host of other compressed filesystems,
these are read-only. The same applies to the crypto-loop filesystem images
that some projects use. This means you have to package tools into the image
to recreate itself when changes are made. This, of course, takes up space
and adds complexity.

In the end, however, the answer is the same as any other in Linux Land. It
all comes down to personal preference. Many of us are creatures of habit,
and many of us are bit-squeezers. I like to make things as simple and small
as possible, and therefore I have chosen to use tmpfs as my root filesystem.
YMMV, as always.

> regards,
> pedro venda.
> -- 
> Pedro João Lopes Venda
> email: pjlv at mega.ist.utl.pt
> http://arrakis.dhis.org

Tom Cameron

More information about the uClibc mailing list