RFC: root mount enhancement (round 2)

[Poul-Henning Kamp]

In message <34EF2360-1B68-4E0C-8CCE-409CE141D0B8 at mac.com>, Marcel Moolenaar wri
tes:

>don't want to enhance: A USB disk cannot always be used as a root
>file system by virtue of the USB stack releasing the root mount
>lock after creating the umass device, but before CAM has created
>the corresponding da device. 

This is a bug which is entirely unrelated to how we find the
root filesystem:  It should simply be fixed by CAM grabing a
root mount lock when activated from USB and releasing it
only when all it's stuff is done.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.