event based initramfs

[Robert Collins]

On Fri, May 11, 2012 at 3:54 PM, Phillip Susi <psusi at ubuntu.com> wrote:
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> I was a bit confused when I saw this uds event.  It is unclear to me why we would want to add upstart to the initramfs.  I think it is important to remember that the the whole purpose of the initramfs is to help the kernel find the root fs, so things that aren't needed to access the root fs really shouldn't be there, lest it add bloat and slow down booting.  After listening to the audio of the session, it seems like there are a few issues people are trying to address with upstart in the initramfs:
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> 1)  Want to fix bugs with mdadm/luks
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> I don't see what this has to do with upstart at all.  If your root is encrypted, then you must prompt for the password before you can continue, so there is no reason to do this event driven rather than procedural.  Luks volumes not mounted at boot should be handled by udisks or something that can interact with the desktop.  mdadm, dmraid, and lvm have already been converted to event driven and handled via udev and are done the same in both the initramfs and in the real system.  The criticism I have of the current system there is that they are automatically added to the initramfs when installed.  The multipath-tools package has a separate -boot flavor that handles copying the binaries and udev rules to the initramfs only if you require it to boot.  I think mdadm, dmraid, cryptsetup, and lvm should follow that same model to avoid adding things to the initramfs that aren't needed there.

So a related issue is dmraid, which is very similar to mdadm. My last
two dmraid machines fail - every time - to activate on boot. The
reason being that the devices they depend upon don't come up fast
enough, and the configuration process isn't event-driven *enough* to
cope; so I type 'dmraid -ay' on every boot. (I've put some time into
fixing it, but as I reboot these machines very rarely, it hasn't hit
my 'fix it now dammit' threshold.) [My third most distant dmraid box
wouldn't boot because the BIOS raid signature wasn't recognised...
that one I fixed asap, I like my disk sizes being calculated correctly
:P]

I'm not saying we should put upstart in the initramfs, just supplying
some data for the discussion :)

-Rob