vfs: introduce file_modified() helper

The combination of file_remove_privs() and file_update_mtime() is
quite common in filesystem ->write_iter() methods.

Modelled after the helper file_accessed(), introduce file_modified()
and use it from generic_remap_file_range_prep().

Note that the order of calling file_remove_privs() before
file_update_mtime() in the helper was matched to the more common order by
filesystems and not the current order in generic_remap_file_range_prep().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

3 files changed, 25 insertions, 18 deletions

diff --git a/fs/inode.c b/fs/inode.c
index df6542ec3b88..4348cfb14562 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1899,6 +1899,26 @@ int file_update_time(struct file *file)
 }
 EXPORT_SYMBOL(file_update_time);
 
+/* Caller must hold the file's inode lock */
+int file_modified(struct file *file)
+{
+        int err;
+
+        /*
+         * Clear the security bits if the process is not being run by root.
+         * This keeps people from modifying setuid and setgid binaries.
+         */
+        err = file_remove_privs(file);
+        if (err)
+                return err;
+
+        if (unlikely(file->f_mode & FMODE_NOCMTIME))
+                return 0;
+
+        return file_update_time(file);
+}
+EXPORT_SYMBOL(file_modified);
+
 int inode_needs_sync(struct inode *inode)
 {
         if (IS_SYNC(inode))
diff --git a/fs/read_write.c b/fs/read_write.c
index b0fb1176b628..cec7e7b1f693 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1980,25 +1980,10 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
                 return ret;
 
         /* If can't alter the file contents, we're done. */
-        if (!(remap_flags & REMAP_FILE_DEDUP)) {
-                /* Update the timestamps, since we can alter file contents. */
-                if (!(file_out->f_mode & FMODE_NOCMTIME)) {
-                        ret = file_update_time(file_out);
-                        if (ret)
-                                return ret;
-                }
+        if (!(remap_flags & REMAP_FILE_DEDUP))
+                ret = file_modified(file_out);
 
-                /*
-                 * Clear the security bits if the process is not being run by
-                 * root.  This keeps people from modifying setuid and setgid
-                 * binaries.
-                 */
-                ret = file_remove_privs(file_out);
-                if (ret)
-                        return ret;
-        }
-
-        return 0;
+        return ret;
 }
 EXPORT_SYMBOL(generic_remap_file_range_prep);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e4d382c4342a..79ffa2958bd8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2177,6 +2177,8 @@ static inline void file_accessed(struct file *file)
                 touch_atime(&file->f_path);
 }
 
+extern int file_modified(struct file *file);
+
 int sync_inode(struct inode *inode, struct writeback_control *wbc);
 int sync_inode_metadata(struct inode *inode, int wait);