[RFC v2] tracing/events: block: also try to get dev_t via driver core for some events

Complements v2.6.31 commit 55782138e47d ("tracing/events: convert block trace points to TRACE_EVENT()") for cases where rq->rq_disk == NULL: block_rq_requeue, block_rq_insert, block_rq_issue; and for cases where bio == NULL: block_getrq, block_sleeprq. NB: The NULL pointer check for

[RFC v2] tracing/events: block: also try to get dev_t via driver core for some events

Complements v2.6.31 commit 55782138e47d ("tracing/events: convert block trace points to TRACE_EVENT()") for cases where rq->rq_disk == NULL: block_rq_requeue, block_rq_insert, block_rq_issue; and for cases where bio == NULL: block_getrq, block_sleeprq. NB: The NULL pointer check for