Re: USB mini-summit at LinuxCon Vancouver

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Hi,

On 08/11/2011 04:56 PM, Alan Stern wrote:
On Thu, 11 Aug 2011, Hans de Goede wrote:

The alternative seems to be to define a device-sharing protocol for USB
drivers.  Kernel drivers would implement a new callback (asking them to
give up control of the device), and usbfs would implement new ioctls by
which a program could ask for and relinquish control of a device.  The
amount of rewriting needed would be relatively small.

A few loose ends would remain, such as how to handle suspends, resumes,
resets, and disconnects.  Assuming usbfs is the only driver that will
want to share a device in this way, we could handle them.

Hans, what do you think?


First of all thanks for the constructive input!

When you say: "device-sharing protocol", do you mean 2 drivers been
attached, but only 1 being active. Or just some additional glue to make
hand-over between them work better?

I was thinking that the webcam driver would always be attached, but
from time to time usbfs would ask to use the device.  When the webcam
driver gives away control, it remains bound to the device but does not
send any URBs.  If it needs to send an URB, first it has to ask usbfs
to give control back.


Oh, interesting...

<snip lots of good stuff>

I'm not claiming that this is a better solution than putting everything
in the kernel.  Just that it is a workable alternative which would
involve a lot less coding.

This is definitely an interesting proposal, something to think about ...

I have 2 concerns wrt this approach:

1) It feels less clean then just having a single driver; and
2) I agree it will be less coding, but I doubt it will really be that much
less work. It will likely need less new code (but a lot can be more or
less copy pasted), but it will need changes across a wider array of
subsystems / userspace components, requiring a lot of coordinating,
getting patches merged in different projects, etc. So in the end I
think it too will be quite a bit of work.

I guess that what I'm trying to say here is, that if we are going to
spend a significant amount of time on this, we might just as well
go for the best solution we can come up with even if that is some
more work.

Regards,

Hans
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