Re: Keep initrd tasks running?

[John Richard Moser <nigelenki@comcast.net>]

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Jeff Bailey wrote:
> Le mardi 18 octobre 2005 à 15:13 -0400, John Richard Moser a écrit :
> 
>>I have no idea who's the best to ask for this.
>>
>>I want to start a task in an initrd and have it stay running after init
>>is started.  Pretty much:
> 
> 
>>What's the feasibility of this without the system balking and vomiting
>>chunks everywhere?  I'm pretty sure 'exec /sbin/init' from linuxrc
>>(PID=1) will replace the process image of sh (linuxrc) with init,
>>keeping PID=1; but I'm worried this may terminate children too.  Haven't
>>tried.
> 
> 
> This is much more easily supported in Breezy.  usplash is started at the
> top of the initramfs (from the init-top hook) and lives until we start
> gdm.
> 

So in short it's possible?

> The biggest constraint is that you don't have write access to the target
> root filesystem (since it's mounted readonly).  However, /dev is a tmpfs
> that is move mounted to the new root system.  If you need to have
> sockets open or store data, you can use that.  usplash does this for its
> socket.
> 

That's not much of a problem for me.  What I'm contemplating is a FUSE
file system driver that gets started in the initrd, and a kernel that
has a file system driver built-in for something stupid like cramfs or MINIX.

The idea is that (as proof of concept) it should be possible to supply
something like ext3 as a FUSE driver, and boot off it as the rootfs
without building ext3 into the kernel or ever modprobing it.  Besides
just being damn cool, and a show of quasi-hybrid microkernelism at work
(uh oh now Linus is going to remove FUSE from mainline :), it'd allow
some real visible macro-benchmarking of FUSE.

> Note that the initramfs startup sequence isn't at all similar to the old
> initrd startups.  It should be easy for you to cleanly add what you want
> under /etc/mkinitramfs/scripts and not have to modify the
> initramfs-tools package.  /usr/share/doc/initramfs-tools/HACKING
> contains some starter information.
> 
> Hope this helps!
> 
> Tks,
> Jeff Bailey
> 
> 
> 
> 

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