tracing: Add alloc_snapshot kernel command line parameter

If debugging the kernel, and the developer wants to use
tracing_snapshot() in places where tracing_snapshot_alloc() may
be difficult (or more likely, the developer is lazy and doesn't
want to bother with tracing_snapshot_alloc() at all), then adding

  alloc_snapshot

to the kernel command line parameter will tell ftrace to allocate
the snapshot buffer (if configured) when it allocates the main
tracing buffer.

I also noticed that ring_buffer_expanded and tracing_selftest_disabled
had inconsistent use of boolean "true" and "false" with "0" and "1".
I cleaned that up too.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 48 insertions, 33 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 57b4220d96a9..4021a5e66412 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -47,7 +47,7 @@
  * On boot up, the ring buffer is set to the minimum size, so that
  * we do not waste memory on systems that are not using tracing.
  */
-int ring_buffer_expanded;
+bool ring_buffer_expanded;
 
 /*
  * We need to change this state when a selftest is running.
@@ -121,12 +121,14 @@ static int tracing_set_tracer(const char *buf);
 static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
 static char *default_bootup_tracer;
 
+static bool allocate_snapshot;
+
 static int __init set_cmdline_ftrace(char *str)
 {
         strncpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);
         default_bootup_tracer = bootup_tracer_buf;
         /* We are using ftrace early, expand it */
-        ring_buffer_expanded = 1;
+        ring_buffer_expanded = true;
         return 1;
 }
 __setup("ftrace=", set_cmdline_ftrace);
@@ -147,6 +149,15 @@ static int __init set_ftrace_dump_on_oops(char *str)
 }
 __setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
 
+static int __init alloc_snapshot(char *str)
+{
+        allocate_snapshot = true;
+        /* We also need the main ring buffer expanded */
+        ring_buffer_expanded = true;
+        return 1;
+}
+__setup("alloc_snapshot", alloc_snapshot);
+
 
 static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
 static char *trace_boot_options __initdata;
@@ -951,7 +962,7 @@ int register_tracer(struct tracer *type)
         tracing_set_tracer(type->name);
         default_bootup_tracer = NULL;
         /* disable other selftests, since this will break it. */
-        tracing_selftest_disabled = 1;
+        tracing_selftest_disabled = true;
 #ifdef CONFIG_FTRACE_STARTUP_TEST
         printk(KERN_INFO "Disabling FTRACE selftests due to running tracer '%s'\n",
                type->name);
@@ -3318,7 +3329,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
          * we use the size that was given, and we can forget about
          * expanding it later.
          */
-        ring_buffer_expanded = 1;
+        ring_buffer_expanded = true;
 
         /* May be called before buffers are initialized */
         if (!tr->trace_buffer.buffer)
@@ -5396,53 +5407,57 @@ static void init_trace_buffers(struct trace_array *tr, struct trace_buffer *buf)
         }
 }
 
-static int allocate_trace_buffers(struct trace_array *tr, int size)
+static int
+allocate_trace_buffer(struct trace_array *tr, struct trace_buffer *buf, int size)
 {
         enum ring_buffer_flags rb_flags;
 
         rb_flags = trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;
 
-        tr->trace_buffer.buffer = ring_buffer_alloc(size, rb_flags);
-        if (!tr->trace_buffer.buffer)
-                goto out_free;
+        buf->buffer = ring_buffer_alloc(size, rb_flags);
+        if (!buf->buffer)
+                return -ENOMEM;
 
-        tr->trace_buffer.data = alloc_percpu(struct trace_array_cpu);
-        if (!tr->trace_buffer.data)
-                goto out_free;
+        buf->data = alloc_percpu(struct trace_array_cpu);
+        if (!buf->data) {
+                ring_buffer_free(buf->buffer);
+                return -ENOMEM;
+        }
 
-        init_trace_buffers(tr, &tr->trace_buffer);
+        init_trace_buffers(tr, buf);
 
         /* Allocate the first page for all buffers */
         set_buffer_entries(&tr->trace_buffer,
                            ring_buffer_size(tr->trace_buffer.buffer, 0));
 
-#ifdef CONFIG_TRACER_MAX_TRACE
-
-        tr->max_buffer.buffer = ring_buffer_alloc(1, rb_flags);
-        if (!tr->max_buffer.buffer)
-                goto out_free;
-
-        tr->max_buffer.data = alloc_percpu(struct trace_array_cpu);
-        if (!tr->max_buffer.data)
-                goto out_free;
+        return 0;
+}
 
-        init_trace_buffers(tr, &tr->max_buffer);
+static int allocate_trace_buffers(struct trace_array *tr, int size)
+{
+        int ret;
 
-        set_buffer_entries(&tr->max_buffer, 1);
-#endif
-        return 0;
+        ret = allocate_trace_buffer(tr, &tr->trace_buffer, size);
+        if (ret)
+                return ret;
 
- out_free:
-        if (tr->trace_buffer.buffer)
+#ifdef CONFIG_TRACER_MAX_TRACE
+        ret = allocate_trace_buffer(tr, &tr->max_buffer,
+                                    allocate_snapshot ? size : 1);
+        if (WARN_ON(ret)) {
                 ring_buffer_free(tr->trace_buffer.buffer);
-        free_percpu(tr->trace_buffer.data);
+                free_percpu(tr->trace_buffer.data);
+                return -ENOMEM;
+        }
+        tr->allocated_snapshot = allocate_snapshot;
 
-#ifdef CONFIG_TRACER_MAX_TRACE
-        if (tr->max_buffer.buffer)
-                ring_buffer_free(tr->max_buffer.buffer);
-        free_percpu(tr->max_buffer.data);
+        /*
+         * Only the top level trace array gets its snapshot allocated
+         * from the kernel command line.
+         */
+        allocate_snapshot = false;
 #endif
-        return -ENOMEM;
+        return 0;
 }
 
 static int new_instance_create(const char *name)