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>

diff --git a/block/Kconfig b/block/Kconfig
index 0cbb3b8..7cdaa1d 100644 (file)
--- 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