linux-kernel - Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting root

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Message-ID: <Pine.LNX.4.64.0804250921090.27978@sbz-30.cs.Helsinki.FI>
Date:	Fri, 25 Apr 2008 09:30:52 +0300 (EEST)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>
cc:	Greg KH <greg@...ah.com>, Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, dsd@...too.org,
	linux-usb@...r.kernel.org, vegardno@....uio.no,
	James.Bottomley@...senPartnership.com, linux-scsi@...r.kernel.org
Subject: Re: [RFC/PATCH] usb-storage: wait for device scanning before mounting
 root

On Thu, 24 Apr 2008, Matthew Dharm wrote:
> This also has all sorts of races between do_mounts 'waiting' and the actual
> USB device enumeration.  It's entirely possible that the kernel loads via
> BIOS, the USB drivers are loaded, that forces devices to disconnect/reset,
> and they take a while to re-enumerate.  During that delay, the kernel gets
> to do_mount; now, no devices show in this "waiting for scan" count.

So how does that happen? ->storage_probe fails and driver core calls it 
later at some point?

On Thu, 24 Apr 2008, Matthew Dharm wrote:
> The right way to do this is via initrd and something like devlabel to wait
> for a specific device to appear.  On some systems, you may want to wait for
> several devices to appear.

You should be able to boot from an external USB disk without initrd. 
That's why we have the current root_delay= hack.

		Pekka
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