blktrace: the ftrace interface needs CONFIG_TRACING

Impact: build fix

Also mention in the help text that blktrace now can be used using
the ftrace interface.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 0 deletions

diff --git a/block/Kconfig b/block/Kconfig
index 0cbb3b88b59a..7cdaa1d72252 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -50,6 +50,8 @@ config BLK_DEV_IO_TRACE
         select RELAY
         select DEBUG_FS
         select TRACEPOINTS
+        select TRACING
+        select STACKTRACE
         help
           Say Y here if you want to be able to trace the block layer actions
           on a given queue. Tracing allows you to see any traffic happening
@@ -58,6 +60,12 @@ config BLK_DEV_IO_TRACE
 
           git://git.kernel.dk/blktrace.git
 
+          Tracing also is possible using the ftrace interface, e.g.:
+
+            echo 1 > /sys/block/sda/sda1/trace/enable
+            echo blk > /sys/kernel/debug/tracing/current_tracer
+            cat /sys/kernel/debug/tracing/trace_pipe
+
           If unsure, say N.
 
 config BLK_DEV_BSG