Re: "legacy" usb stack fixes

From: Julian Elischer <julian_at_elischer.org>
Date: Thu, 11 Sep 2008 09:23:10 -0700
Rink Springer wrote:
> On Thu, Sep 11, 2008 at 10:13:22AM +0200, Hans Petter Selasky wrote:
>> I also see crashes with my new stuff and the umass driver when the USB device 
>> is un-plugged too early. The backtraces I've got so far does not indicate a 
>> USB problem, though ....
> 
> That is correct, this is a bug in CAM. More specifically, CAM does not
> handle the removal of busses well. There are two possible options:
> 
> 1) Obviously, fix CAM to handle this scenarion
>    DragonflyBSD seems to have a lot of fixes in this area, which I
>    intend to take a look at 'some day' (no thanks to $reallife...)
> 
> 2) Create a CAM bus per USB bus
>   I think this is reasonable, and it makes a lot more sense than the
>    one-bus-per-device approach that we have now. The idea is that
>    every USB controller hub creates a CAM bus, and umass(4) attaches to
>    this bus instead of creating its own. Of course, until CAM is fixed,
>    detaching PCMCIA or equivalent USB cards will still cause panics, but
>    it would be a lot better than it is now...
> 

This is how it was originally. There was a reason that it was
changed, so make sure you look into the history to figure out
what the tradeoff was.

> Personally, I'd like to see option 2 implemented in the USB2 stack, as
> it avoids the issue and makes a lot more sense from user perspective
> (I'm probably onot the only one who gets scared by 'camcontrol devlist'
> if you have a single MP3 player which advertises 2 disks :-))
> 
> Regards,
> 
Received on Thu Sep 11 2008 - 14:23:10 UTC

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