linux-kernel - USB stick as root device does not work

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Date:	Sun, 22 May 2011 16:13:17 +0200
From:	Micha Nelissen <micha@...i.hopto.org>
To:	linux-kernel@...r.kernel.org
Subject: USB stick as root device does not work

Hi,

Using USB stick as root device does not work for me. I specify
'root=/dev/sdb1 rootwait' on the kernel commandline, but the kernel does
not wait for the USB stick to be scanned and its partitions found. I
have a harddisk which is /dev/sda, and this USB stick would be /dev/sdb.

I think blk_lookup_devt returns the block device number even if it does
not exist yet, and init/do_mounts.c:473 therefore skips waiting:

        if ((ROOT_DEV == 0) && root_wait) {

due to ROOT_DEV having become non-zero already.

If I use the commandline: 'root=/dev/sdb1 rootdelay=5' then it does
mount and boot properly. However, using rootwait seems safer and faster
to me, that it's meant for this use case.

Thanks for any pointers,

Micha
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