Re: [PATCH 1/5] initdev:kernel: Asynchronously-discovered device synchronization, v5

Arjan van de Ven
2009-05-03T23:19:57Z

On Sat, 2 May 2009 13:55:45 -0400 (EDT)
Alan Stern <stern@rowland.harvard.edu> wrote:

> On Sat, 2 May 2009, James Bottomley wrote:
>
> > OK, so in your scheme, I get why console devices: they need to be
> > present early before we start dumping console output otherwise it
> > can get lost.
> >
> > However, I don't see the need for either network or block.
> >
> > For network, the only early discovery use is net root (which can be
> > done fully asynchronously)
>
> Are you referring to the "rootwait" kernel parameter? Is there a
> reason why this is a boot-time parameter instead of always being
> set? I mean, under what circumstances would you _not_ want to wait
> until the root device is present?

if you have an initrd ;-)
>
> Perhaps with some enterprise systems, it is preferred to have the
> system fail with an explicit error message rather than wait
> indefinitely...

actually, in an enterprise system, you want to reboot.
The bootloader might boot a different kernel the next time
that is known to work.
(for example, the current kernel might have been booted with the "once"
grub option)
>
> > What I'm getting at is that I don't see the benefit of this in the
> > light of Arjan's async boot system, which can also tell us when all
> > discovery is complete ... what added benefit am I missing here?
>
> How does Arjan's async boot system tell use when all discovery is
> complete? AFAICS, it only tells you when all its async tasks are
> finished. But device discovery and registration sometimes use other
> asynchronous techniques which Arjan's code is unaware of.
> Examples: the USB khubd thread, the USB mass-storage scanning thread,
> and the SCSI async-scanning thread.

for normal device probing we already have infrastructure though...
wait_for_device_probe, driver_probe_done and friends...
(the scsi scanning thread is being converted to the async
infrastructure btw)

do we need to invent more ?

--
Arjan van de Ven Intel Open Source Technology Centre
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