fs: add a vfs_fchown helper

Add a helper for struct file based chown operations.  To be used by
the initramfs code soon.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/open.c

@@ -740,23 +740,28 @@ SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group
 			   AT_SYMLINK_NOFOLLOW);
 }
 
+int vfs_fchown(struct file *file, uid_t user, gid_t group)
+{
+	int error;
+
+	error = mnt_want_write_file(file);
+	if (error)
+		return error;
+	audit_file(file);
+	error = chown_common(&file->f_path, user, group);
+	mnt_drop_write_file(file);
+	return error;
+}
+
 int ksys_fchown(unsigned int fd, uid_t user, gid_t group)
 {
 	struct fd f = fdget(fd);
 	int error = -EBADF;
 
-	if (!f.file)
-		goto out;
-
-	error = mnt_want_write_file(f.file);
-	if (error)
-		goto out_fput;
-	audit_file(f.file);
-	error = chown_common(&f.file->f_path, user, group);
-	mnt_drop_write_file(f.file);
-out_fput:
-	fdput(f);
-out:
+	if (f.file) {
+		error = vfs_fchown(f.file, user, group);
+		fdput(f);
+	}
 	return error;
 }
 

include/linux/fs.h

@@ -1744,6 +1744,8 @@ int vfs_mkobj(struct dentry *, umode_t,
 		int (*f)(struct dentry *, umode_t, void *),
 		void *);
 
+int vfs_fchown(struct file *file, uid_t user, gid_t group);
+
 extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 
 #ifdef CONFIG_COMPAT