tree d4e2f930850eb3981307a3eec8c86399dcebf68a
parent 482c083492ddaa32ef5864bae3d143dc8bcdf7d1
author NeilBrown <neilb@suse.de> 1303115142 +1000
committer NeilBrown <neilb@suse.de> 1303115142 +1000

md: provide generic support for handling unplug callbacks.

When an md device adds a request to a queue, it can call
mddev_check_plugged.
If this succeeds then we know that the md thread will be woken up
shortly, and ->plug_cnt will be non-zero until then, so some
processing can be delayed.

If it fails, then no unplug callback is expected and the make_request
function needs to do whatever is required to make the request happen.

Signed-off-by: NeilBrown <neilb@suse.de>