usb4bsd patch review

[Poul-Henning Kamp]

In message <20080823.223951.-962047221.imp at bsdimp.com>, "M. Warner Losh" writes
:
>In message: <10826.1219511738 at critter.freebsd.dk>
>            "Poul-Henning Kamp" <phk at phk.freebsd.dk> writes:
>: In message <20080823.100155.1310242209.imp at bsdimp.com>, "M. Warner Losh" writes
>: :
>: 
>: >While this may be a good idea, I'm hesitant about races that it may
>: >introduce.  This is the classic point of attack: do something between
>: >steps of a formerly atomic operation that was made non-atomic.  I
>: >can't think of anything off the top of my head, but I'm still
>: >concerned.
>: 
>: We have ways of closing the race if need be, but they're all slightly
>: kludgy, but I am not overly concerned about those races as long as
>: the default is to not give access.
>
>I guess I'm worried about a device that comes and goes and comes back
>and there being some difference between the two that causes us to
>bogusly do something to the new device that was appropriate for the
>old one, but not the new one...

That scenario is always present as far as I can tell...

-- 
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.