Re: [PATCH 05/12] erofs: drop posix acl handlers

[Christoph Hellwig <hch@lst.de>]

This review is not for erofs specifically, but for all file systems using
the same scheme.

> +static const char *erofs_xattr_prefix(int xattr_index, struct dentry *dentry)
> +{
> +	const char *name = NULL;
> +	const struct xattr_handler *handler = NULL;
> +
> +	switch (xattr_index) {
> +	case EROFS_XATTR_INDEX_USER:
> +		handler = &erofs_xattr_user_handler;
> +		break;
> +	case EROFS_XATTR_INDEX_TRUSTED:
> +		handler = &erofs_xattr_trusted_handler;
> +		break;
> +#ifdef CONFIG_EROFS_FS_SECURITY
> +	case EROFS_XATTR_INDEX_SECURITY:
> +		handler = &erofs_xattr_security_handler;
> +		break;
> +#endif
> +#ifdef CONFIG_EROFS_FS_POSIX_ACL
> +	case EROFS_XATTR_INDEX_POSIX_ACL_ACCESS:
> +		if (posix_acl_dentry_list(dentry))
> +			name = XATTR_NAME_POSIX_ACL_ACCESS;
> +		break;
> +	case EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT:
> +		if (posix_acl_dentry_list(dentry))
> +			name = XATTR_NAME_POSIX_ACL_DEFAULT;
> +		break;
> +#endif
> +	default:
> +		return NULL;
> +	}
> +
> +	if (xattr_dentry_list(handler, dentry))
> +		name = xattr_prefix(handler);

I'm not a huge fan of all this duplicate logic in the file systems
that is more verbose and a bit confusing.  Until we remove the
xattr handlers entirely, I wonder if we just need to keep a
special ->list for posix xattrs, just to be able to keep the
old logic in all these file system.  That is a ->list that
works for xattr_dentry_list, but never actually lists anything.

That would remove all this boiler plate for now without minimal
core additions.  Eventually we can hopefully remove first ->list
and then the xattr handlers entirely, but until then this seems
like a step backwards.