tracing/boot: Add ftrace.instance.*.alloc_snapshot option

Add ftrace.instance.*.alloc_snapshot option.

This option has been described in Documentation/trace/boottime-trace.rst
but not implemented yet.

ftrace.[instance.INSTANCE.]alloc_snapshot
   Allocate snapshot buffer.

The difference from kernel.alloc_snapshot is that the kernel.alloc_snapshot
will allocate the buffer only for the main instance, but this can allocate
buffer for any new instances.

Link: https://lkml.kernel.org/r/160234368948.400560.15313384470765915015.stgit@devnote2
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 754e3cf..c22a152 100644 (file)
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -284,6 +284,12 @@ trace_boot_enable_tracer(struct trace_array *tr, struct xbc_node *node)
                if (tracing_set_tracer(tr, p) < 0)
                        pr_err("Failed to set given tracer: %s\n", p);
        }
+
+       /* Since tracer can free snapshot buffer, allocate snapshot here.*/
+       if (xbc_node_find_value(node, "alloc_snapshot", NULL)) {
+               if (tracing_alloc_snapshot_instance(tr) < 0)
+                       pr_err("Failed to allocate snapshot buffer\n");
+       }
 }
 
 static void __init