ftrace: inject markers via trace_marker file

Allow a user to inject a marker (TRACE_PRINT entry) into the trace ring
buffer. The related file operations are derived from code by Frédéric
Weisbecker <fweisbec@gmail.com>.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 75 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7e7154f77009..eee1fd964898 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2879,6 +2879,66 @@ tracing_entries_write(struct file *filp, const char __user *ubuf,
         return cnt;
 }
 
+static int tracing_open_mark(struct inode *inode, struct file *filp)
+{
+        int ret;
+
+        ret = tracing_open_generic(inode, filp);
+        if (ret)
+                return ret;
+
+        if (current_trace == &no_tracer)
+                return -ENODEV;
+
+        return 0;
+}
+
+static int mark_printk(const char *fmt, ...)
+{
+        int ret;
+        va_list args;
+        va_start(args, fmt);
+        ret = trace_vprintk(0, fmt, args);
+        va_end(args);
+        return ret;
+}
+
+static ssize_t
+tracing_mark_write(struct file *filp, const char __user *ubuf,
+                                        size_t cnt, loff_t *fpos)
+{
+        char *buf;
+        char *end;
+        struct trace_array *tr = &global_trace;
+
+        if (current_trace == &no_tracer || !tr->ctrl || tracing_disabled)
+                return -EINVAL;
+
+        if (cnt > TRACE_BUF_SIZE)
+                cnt = TRACE_BUF_SIZE;
+
+        buf = kmalloc(cnt + 1, GFP_KERNEL);
+        if (buf == NULL)
+                return -ENOMEM;
+
+        if (copy_from_user(buf, ubuf, cnt)) {
+                kfree(buf);
+                return -EFAULT;
+        }
+
+        /* Cut from the first nil or newline. */
+        buf[cnt] = '\0';
+        end = strchr(buf, '\n');
+        if (end)
+                *end = '\0';
+
+        cnt = mark_printk("%s\n", buf);
+        kfree(buf);
+        *fpos += cnt;
+
+        return cnt;
+}
+
 static struct file_operations tracing_max_lat_fops = {
         .open           = tracing_open_generic,
         .read           = tracing_max_lat_read,
@@ -2910,6 +2970,11 @@ static struct file_operations tracing_entries_fops = {
         .write          = tracing_entries_write,
 };
 
+static struct file_operations tracing_mark_fops = {
+        .open           = tracing_open_mark,
+        .write          = tracing_mark_write,
+};
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 static ssize_t
@@ -3027,6 +3092,12 @@ static __init void tracer_init_debugfs(void)
                 pr_warning("Could not create debugfs "
                            "'trace_entries' entry\n");
 
+        entry = debugfs_create_file("trace_marker", 0220, d_tracer,
+                                    NULL, &tracing_mark_fops);
+        if (!entry)
+                pr_warning("Could not create debugfs "
+                           "'trace_marker' entry\n");
+
 #ifdef CONFIG_DYNAMIC_FTRACE
         entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
                                     &ftrace_update_tot_cnt,
@@ -3040,11 +3111,6 @@ static __init void tracer_init_debugfs(void)
 #endif
 }
 
-#define TRACE_BUF_SIZE 1024
-#define TRACE_PRINT_BUF_SIZE \
-        (sizeof(struct trace_field) - offsetof(struct trace_field, print.buf))
-#define TRACE_CONT_BUF_SIZE sizeof(struct trace_field)
-
 int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 {
         static DEFINE_SPINLOCK(trace_buf_lock);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 648433d18ccb..42f65d0097f0 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -124,6 +124,10 @@ struct trace_entry {
 };
 
 #define TRACE_ENTRY_SIZE        sizeof(struct trace_entry)
+#define TRACE_BUF_SIZE          1024
+#define TRACE_PRINT_BUF_SIZE \
+        (sizeof(struct trace_field) - offsetof(struct trace_field, print.buf))
+#define TRACE_CONT_BUF_SIZE     sizeof(struct trace_field)
 
 /*
  * The CPU trace array - it consists of thousands of trace entries