f2fs: use generic checking and prep function for FS_IOC_SETFLAGS

Make the f2fs implementation of FS_IOC_SETFLAGS use the new VFS helper
function vfs_ioc_setflags_prepare().

This is based on a patch from Darrick Wong, but reworked to apply after
commit 36098557 ("f2fs: separate f2fs i_flags from fs_flags and ext4
i_flags").

Originally-from: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -1770,7 +1770,8 @@ static int f2fs_ioc_getflags(struct file *filp, unsigned long arg)
 static int f2fs_ioc_setflags(struct file *filp, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
-	u32 fsflags;
+	struct f2fs_inode_info *fi = F2FS_I(inode);
+	u32 fsflags, old_fsflags;
 	u32 iflags;
 	int ret;
 
@@ -1794,8 +1795,14 @@ static int f2fs_ioc_setflags(struct file *filp, unsigned long arg)
 
 	inode_lock(inode);
 
+	old_fsflags = f2fs_iflags_to_fsflags(fi->i_flags);
+	ret = vfs_ioc_setflags_prepare(inode, old_fsflags, fsflags);
+	if (ret)
+		goto out;
+
 	ret = f2fs_setflags_common(inode, iflags,
 			f2fs_fsflags_to_iflags(F2FS_SETTABLE_FS_FL));
+out:
 	inode_unlock(inode);
 	mnt_drop_write_file(filp);
 	return ret;