[Gllug] Hotplug and diet Libc

Dave Jones davej at suse.de
Tue Apr 30 16:49:34 UTC 2002

On Tue, Apr 30, 2002 at 01:49:19PM +0200, John Hearns wrote:
 > I've just read a very good article on Linux Hotplug,
 > in the April Linux Journal (sorry, not online).
 > http://linux-hotplug.sourceforge.net

Yep, most people liked Greg's articles so much they let Linux Journal
know. LJ seemed to take notice, and offered him a monthly column
aparently on device drivers, looking forward to more interesting
writings from him.

 > I was very interested in the plans for the 2.5 series
 > to implement a small user-space environment at boot time-
 > (diet)Hotplug.
 > This is something I hadn't heard of before.
 > http://lwn.net/2001/0712/kernel.php
 > Obviously something to be very aware of!

To most users, this will be completely transparent. It's unlikely to
even show up in the options when you build a kernel.  The idea is
essentially glue a cpio archive to the end of the kernel image,
unpack it to ramfs, run init(1) from there, which will do whatever
early userspace trickery deemed necessary, and then hand off control
to the real init(1) that lives on the hard disk.

Neat idea that's going to clean up quite a few icky areas of the kernel.

One tricky bit is going to be throwing this stuff away after you've
used it. A compulsory initrd is a nice idea, but quite a few users of
low-end low memory boxes aren't going to be too amused to have a hundred
KB or so of early-userspace still sitting around in memory. No doubt
it'll get figured out. Still early days yet.

 > This also uses something called diet libc - 
 > a stripped down, lean libc
 > http://www.fefe.de/dietlibc/

diethotplug uses this currently, but there have actually been proposals
for a 'kernel libc' for the early boot stuff, which seems more about
control than anything else. Again, time will tell.


| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

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