vfs: create a generic checking and prep function for FS_IOC_SETFLAGS

Create a generic function to check incoming FS_IOC_SETFLAGS flag values
and later prepare the inode for updates so that we can standardize the
implementations that follow ext4's flag values.

Note that the efivarfs implementation no longer fails a no-op SETFLAGS
without CAP_LINUX_IMMUTABLE since that's the behavior in ext*.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Sterba <dsterba@suse.com>
Reviewed-by: Bob Peterson <rpeterso@redhat.com>

fs/nilfs2/ioctl.c

@@ -148,13 +148,8 @@ static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 
 	oldflags = NILFS_I(inode)->i_flags;
 
-	/*
-	 * The IMMUTABLE and APPEND_ONLY flags can only be changed by the
-	 * relevant capability.
-	 */
-	ret = -EPERM;
-	if (((flags ^ oldflags) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) &&
-	    !capable(CAP_LINUX_IMMUTABLE))
+	ret = vfs_ioc_setflags_prepare(inode, oldflags, flags);
+	if (ret)
 		goto out;
 
 	ret = nilfs_transaction_begin(inode->i_sb, &ti, 0);