tracing: Make a snapshot feature available from userspace
Ftrace has a snapshot feature available from kernel space and
latency tracers (e.g. irqsoff) are using it. This patch enables
user applictions to take a snapshot via debugfs.
Add "snapshot" debugfs file in "tracing" directory.
snapshot:
This is used to take a snapshot and to read the output of the
snapshot.
# echo 1 > snapshot
This will allocate the spare buffer for snapshot (if it is
not allocated), and take a snapshot.
# cat snapshot
This will show contents of the snapshot.
# echo 0 > snapshot
This will free the snapshot if it is allocated.
Any other positive values will clear the snapshot contents if
the snapshot is allocated, or return EINVAL if it is not allocated.
Link: http://lkml.kernel.org/r/20121226025300.3252.86850.stgit@liselsia
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: David Sharp <dhsharp@google.com>
Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
[
Fixed irqsoff selftest and also a conflict with a change
that fixes the update_max_tr.
]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index cdc9d28..3656756 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -253,6 +253,16 @@
help
Basic tracer to catch the syscall entry and exit events.
+config TRACER_SNAPSHOT
+ bool "Create a snapshot trace buffer"
+ select TRACER_MAX_TRACE
+ help
+ Allow tracing users to take snapshot of the current buffer using the
+ ftrace interface, e.g.:
+
+ echo 1 > /sys/kernel/debug/tracing/snapshot
+ cat snapshot
+
config TRACE_BRANCH_PROFILING
bool
select GENERIC_TRACER