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>