[PATCH 1/1] tracing/boot: Add ftrace.instance.*.alloc_snapshot option

[Masami Hiramatsu <mhiramat@kernel.org>]

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.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 kernel/trace/trace_boot.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 754e3cf2df3a..c22a152ef0b4 100644
--- 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