Re: handling timeouts on usb_bulk_msg

[Rogier Wolff <R.E.Wolff@xxxxxxxxxxxx>]

On Mon, Nov 05, 2007 at 04:10:35PM -0500, Alan Stern wrote:
> On Mon, 5 Nov 2007, Andrew Greensted wrote:
> 
> > Hi All,
> > 
> > I've written a custom device driver based on the usb-skeleton.c file in
> > the kernel source.
> > 
> > I want the driver to act in a similar way to when you read from a serial
> > port. ie, when you do this:
> > 
> > cat /dev/ttyS0
> > 
> > it will wait for data to appear on the port and output to the terminal.
> > It doesn't timeout, or close the connection when no data is available.
> > In my case the data source is an IN endpoint from a custom usb board.
> > 
> > The problem is how do I stop cat (or any other program) closing the
> > connection when the read function timesout (the condition when no data
> > is yet available).
> > 
> > I've tried checking to see if the return value from usb_bulk_msg is
> > ETIMEDOUT and returning 0 (no bytes read) from my read function rather
> > than the error, but cat still exits.

If you return "0" on the timeout, standard unix interfaces define this
as end-of-file. So cat is correct in interpreting this as EOF and
exiting.

In your driver, you should NOT return if you get the ETIMEDOUT return, 
and simply call usb_bulk_msg again. This is entirely acceptable. 

You will find that doing something about signals is worth the trouble.

	Roger. 

-- 
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