hi all,
in my driver i need to provide synchronous read/write
operations to the application. moreover, operation
cancellation is also needed.
-what is the most recommended way to wait for completion of an urb?
Submit using usb_submit_urb(), then if you don't need operation cancellation, use <linux/completion.h> primitives to wait.
If you need cancelation, <linux/wait.h> primitives are one option, like:
- wait_event_interruptible() - wait_event_interruptible_timeout()
Yes, there's no wait_event_timeout() without the option of breaking out on interrupts; sigh. But it seems like you don't need that option.
When those primitives complete "early", then call usb_unlink_urb() and then use wait_event() to catch the canceled URB. (Even if you gave up just a smidgeon too early, and it already completed...)
You can use a struct completion with these, and have the urb completion handler calling complete().
There's another wait/synchronize primitive that I found at one point, I think the block layer used it, which involved a bit less inlined code and didn't necessarily require everything to be interruptible. I lost track of it though.
-i was planning to use a modified version of usb_start_wait_urb() used inside usb_bulk_msg()
is any better methods possible?
Absolutely. That code needs to be replaced, it's not even correct in certain cases.
- Dave
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