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Date:      Sun, 24 Aug 2008 06:00:10 +0000
From:      "Poul-Henning Kamp" <phk@phk.freebsd.dk>
To:        "M. Warner Losh" <imp@bsdimp.com>
Cc:        freebsd-usb@freebsd.org
Subject:   Re: usb4bsd patch review 
Message-ID:  <13745.1219557610@critter.freebsd.dk>
In-Reply-To: Your message of "Sat, 23 Aug 2008 22:39:51 CST." <20080823.223951.-962047221.imp@bsdimp.com> 

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In message <20080823.223951.-962047221.imp@bsdimp.com>, "M. Warner Losh" writes
:
>In message: <10826.1219511738@critter.freebsd.dk>
>            "Poul-Henning Kamp" <phk@phk.freebsd.dk> writes:
>: In message <20080823.100155.1310242209.imp@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@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.



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