tracing: Add generic tracing_lseek() function

Trace event triggers added a lseek that uses the ftrace_filter_lseek()
function. Unfortunately, when function tracing is not configured in
that function is not defined and the kernel fails to build.

This is the second time that function was added to a file ops and
it broke the build due to requiring special config dependencies.

Make a generic tracing_lseek() that all the tracing utilities may
use.

Also, modify the old ftrace_filter_lseek() to return 0 instead of
1 on WRONLY. Not sure why it was a 1 as that does not make sense.

This also changes the old tracing_seek() to modify the file pos
pointer on WRONLY as well.

Reported-by: kbuild test robot <[e-mail]>
Tested-by: Tom Zanussi <[e-mail]>
Acked-by: Tom Zanussi <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>

include/linux/ftrace.h

···
 ftrace_regex_release(struct inode *inode, struct file *file) { return -ENODEV; }
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
-loff_t ftrace_filter_lseek(struct file *file, loff_t offset, int whence);
-
 /* totally disable ftrace - can not re-enable after this */
 void ftrace_kill(void);
 

kernel/trace/ftrace.c

···
 
 static struct pid * const ftrace_swapper_pid = &init_struct_pid;
 
-loff_t
-ftrace_filter_lseek(struct file *file, loff_t offset, int whence)
-{
-	loff_t ret;
-
-	if (file->f_mode & FMODE_READ)
-		ret = seq_lseek(file, offset, whence);
-	else
-		file->f_pos = ret = 1;
-
-	return ret;
-}
-
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 #ifndef CONFIG_FTRACE_MCOUNT_RECORD
···
  * routine, you can use ftrace_filter_write() for the write
  * routine if @flag has FTRACE_ITER_FILTER set, or
  * ftrace_notrace_write() if @flag has FTRACE_ITER_NOTRACE set.
- * ftrace_filter_lseek() should be used as the lseek routine, and
+ * tracing_lseek() should be used as the lseek routine, and
  * release must call ftrace_regex_release().
  */
 int
···
 	.open = ftrace_filter_open,
 	.read = seq_read,
 	.write = ftrace_filter_write,
-	.llseek = ftrace_filter_lseek,
+	.llseek = tracing_lseek,
 	.release = ftrace_regex_release,
 };
 
···
 	.open = ftrace_notrace_open,
 	.read = seq_read,
 	.write = ftrace_notrace_write,
-	.llseek = ftrace_filter_lseek,
+	.llseek = tracing_lseek,
 	.release = ftrace_regex_release,
 };
 
···
 	.open		= ftrace_graph_open,
 	.read		= seq_read,
 	.write		= ftrace_graph_write,
-	.llseek		= ftrace_filter_lseek,
+	.llseek		= tracing_lseek,
 	.release	= ftrace_graph_release,
 };
 
···
 	.open		= ftrace_graph_notrace_open,
 	.read		= seq_read,
 	.write		= ftrace_graph_write,
-	.llseek		= ftrace_filter_lseek,
+	.llseek		= tracing_lseek,
 	.release	= ftrace_graph_release,
 };
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
···
 	.open		= ftrace_pid_open,
 	.write		= ftrace_pid_write,
 	.read		= seq_read,
-	.llseek		= ftrace_filter_lseek,
+	.llseek		= tracing_lseek,
 	.release	= ftrace_pid_release,
 };
 

kernel/trace/trace.c

···
 	return count;
 }
 
-static loff_t tracing_seek(struct file *file, loff_t offset, int origin)
+loff_t tracing_lseek(struct file *file, loff_t offset, int whence)
 {
+	int ret;
+
 	if (file->f_mode & FMODE_READ)
-		return seq_lseek(file, offset, origin);
+		ret = seq_lseek(file, offset, whence);
 	else
-		return 0;
+		file->f_pos = ret = 0;
+
+	return ret;
 }
 
 static const struct file_operations tracing_fops = {
 	.open		= tracing_open,
 	.read		= seq_read,
 	.write		= tracing_write_stub,
-	.llseek		= tracing_seek,
+	.llseek		= tracing_lseek,
 	.release	= tracing_release,
 };
 
···
 	.open		= tracing_snapshot_open,
 	.read		= seq_read,
 	.write		= tracing_snapshot_write,
-	.llseek		= tracing_seek,
+	.llseek		= tracing_lseek,
 	.release	= tracing_snapshot_release,
 };
 

kernel/trace/trace.h

···
 int register_tracer(struct tracer *type);
 int is_tracing_stopped(void);
 
+loff_t tracing_lseek(struct file *file, loff_t offset, int whence);
+
 extern cpumask_var_t __read_mostly tracing_buffer_mask;
 
 #define for_each_tracing_cpu(cpu)	\

kernel/trace/trace_events_trigger.c

···
 	.open = event_trigger_open,
 	.read = seq_read,
 	.write = event_trigger_write,
-	.llseek = ftrace_filter_lseek,
+	.llseek = tracing_lseek,
 	.release = event_trigger_release,
 };
 

kernel/trace/trace_stack.c

···
 	.open = stack_trace_filter_open,
 	.read = seq_read,
 	.write = ftrace_filter_write,
-	.llseek = ftrace_filter_lseek,
+	.llseek = tracing_lseek,
 	.release = ftrace_regex_release,
 };