[PATCH v2] blktrace: Don't output messages if NOTIFY isn't set.

[Tao Ma]

Now if we enable blktrace, cfq has too many messages output to the
trace buffer. It is fine if we don't specify any action mask.
But if I do like this:
blktrace /dev/sdb -a issue -a complete -o - | blkparse -i -
I only want to see 'D' and 'C', while with the following command
dd if=/mnt/ocfs2/test of=/dev/null bs=4k count=1 iflag=direct

I will get(with a 2.6.37 vanilla kernel):
  8,16   0        0     0.000000000     0  m   N cfq3805 alloced
  8,16   0        0     0.000004126     0  m   N cfq3805 insert_request
  8,16   0        0     0.000004884     0  m   N cfq3805 add_to_rr
  8,16   0        0     0.000008417     0  m   N cfq workload slice:300
  8,16   0        0     0.000009557     0  m   N cfq3805 set_active wl_prio:0 wl_type:2
  8,16   0        0     0.000010640     0  m   N cfq3805 fifo=          (null)
  8,16   0        0     0.000011193     0  m   N cfq3805 dispatch_insert
  8,16   0        0     0.000012221     0  m   N cfq3805 dispatched a request
  8,16   0        0     0.000012802     0  m   N cfq3805 activate rq, drv=1
  8,16   0        1     0.000013181  3805  D   R 114759 + 8 [dd]
  8,16   0        2     0.000164244     0  C   R 114759 + 8 [0]
  8,16   0        0     0.000167997     0  m   N cfq3805 complete rqnoidle 0
  8,16   0        0     0.000168782     0  m   N cfq3805 set_slice=100
  8,16   0        0     0.000169874     0  m   N cfq3805 arm_idle: 8 group_idle: 0
  8,16   0        0     0.000170189     0  m   N cfq schedule dispatch
  8,16   0        0     0.000397938     0  m   N cfq3805 slice expired t=0
  8,16   0        0     0.000399763     0  m   N cfq3805 sl_used=1 disp=1 charge=1 iops=0 sect=8
  8,16   0        0     0.000400227     0  m   N cfq3805 del_from_rr
  8,16   0        0     0.000400882     0  m   N cfq3805 put_queue

See, there are 19 lines while I only need 2. I don't think it is
appropriate for a user.

So this patch will disable any messages if the BLK_TC_NOTIFY isn't set.
Now the output for the same command will look like:
  8,16   0        1     0.000000000  4908  D   R 114759 + 8 [dd]
  8,16   0        2     0.000146827     0  C   R 114759 + 8 [0]

Yes, it is what I want to see.

Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
---
 kernel/trace/blktrace.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 153562d..d95721f 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -138,6 +138,13 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
 		     !blk_tracer_enabled))
 		return;
 
+	/*
+	 * If the BLK_TC_NOTIFY action mask isn't set, don't send any note
+	 * message to the trace.
+	 */
+	if (!(bt->act_mask & BLK_TC_NOTIFY))
+		return;
+
 	local_irq_save(flags);
 	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
 	va_start(args, fmt);
-- 
1.6.3.GIT

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