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

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Message-ID: <20090504074522.13f1ed77@infradead.org>
Date:	Mon, 4 May 2009 07:45:22 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	David VomLehn <dvomlehn@...co.com>,
	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	<linux-usb@...r.kernel.org>, <greg@...ah.com>,
	<linux-scsi@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/5] initdev:kernel: Asynchronously-discovered device
 synchronization, v5

On Mon, 4 May 2009 10:30:06 -0400 (EDT)
Alan Stern <stern@...land.harvard.edu> wrote:

> On Sun, 3 May 2009, Arjan van de Ven wrote:
> 
> > > 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)
> 
> Which makes it imperative that the system knows when all the block
> devices have been probed, so it can stop waiting.
> 
> > > 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 ?
> 
> I suppose the usb-storage scanning thread could also be converted to 
> the async infrastructure, although I haven't heard of anybody working 
> on it.
> 
> But the USB hub driver's thread (khubd) cannot be converted.  It is 
> central to the discovery of USB-based block devices.  How would you 
> handle that?

take a ref in the driver_probe_done() sense, and release it when you
know you're done probing....

at that point all existing infrastructure will just work.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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