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 <fengguang.wu@intel.com>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 59bf5b56ccc0..e32a2f48dde1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3183,19 +3183,23 @@ tracing_write_stub(struct file *filp, const char __user *ubuf,
         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,
 };
 
@@ -4940,7 +4944,7 @@ static const struct file_operations snapshot_fops = {
         .open           = tracing_snapshot_open,
         .read           = seq_read,
         .write          = tracing_snapshot_write,
-        .llseek         = tracing_seek,
+        .llseek         = tracing_lseek,
         .release        = tracing_snapshot_release,
 };