blktrace: add trace/ to /sys/block/sda

Impact: allow ftrace-plugin blktrace to trace device-mapper devices

To trace a single partition:
  # echo 1 > /sys/block/sda/sda1/enable

To trace the whole sda instead:
  # echo 1 > /sys/block/sda/enable

Thus we also fix an issue reported by Ted, that ftrace-plugin blktrace
can't be used to trace device-mapper devices.

Now:

  # echo 1 > /sys/block/dm-0/trace/enable
  echo: write error: No such device or address
  # mount -t ext4 /dev/dm-0 /mnt
  # echo 1 > /sys/block/dm-0/trace/enable
  # echo blk > /debug/tracing/current_tracer

Reported-by: Theodore Tso <tytso@mit.edu>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Shawn Du <duyuyang@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
LKML-Reference: <49E42665.6020506@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index d10989880520..8e7c5da3a3e6 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1644,3 +1644,8 @@ out:
         return ret ? ret : count;
 }
 
+int blk_trace_init_sysfs(struct device *dev)
+{
+        return sysfs_create_group(&dev->kobj, &blk_trace_attr_group);
+}
+