Waiting to get a free request entry in queue for block io operation
void trace_block_sleeprq(struct request_queue * q, struct bio * bio, int rw);
q
queue for operation
bio
pending block IO operation
rw
low bit indicates a read (0) or a write (1)
In the case where a request struct cannot be provided for queue q the process needs to wait for an request struct to become available. This tracepoint event is generated each time the process goes to sleep waiting for request struct become available.