Re: [PATCH] libfs: Attempt exact-match comparison first during casefold lookup

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Jan 17, 2024 at 07:28:36PM -0300, Gabriel Krisman Bertazi wrote:

> Note that, for strict mode, generic_ci_d_compare used to reject an
> invalid UTF-8 string, which would now be considered valid if it
> exact-matches the disk-name.  But, if that is the case, the filesystem
> is corrupt.  More than that, it really doesn't matter in practice,
> because the name-under-lookup will have already been rejected by
> generic_ci_d_hash and we won't even get here.

> -	if (ret >= 0)
> -		return ret;
> -
> -	if (sb_has_strict_encoding(sb))
> +	qstr.len = len;
> +	qstr.name = str;
> +	ret = utf8_strncasecmp(dentry->d_sb->s_encoding, name, &qstr);
> +	if (ret < 0)
>  		return -EINVAL;

Umm...  So why bother with -EINVAL?  The rest looks sane, but
considering the fact that your string *has* passed ->d_hash(),
do we need anything beyond
	return utf8_strncasecmp(dentry->d_sb->s_encoding, name, &qstr);
here?