Re: [RFC PATCH] fs: Plumb case sensitivity bits into statx

[Christoph Hellwig <hch@infradead.org>]

On Thu, Sep 25, 2025 at 11:11:40AM -0400, Chuck Lever wrote:
> +	if (request_mask & STATX_CASE_INFO) {
> +		stat->result_mask |= STATX_CASE_INFO;
> +		/* STATX_CASE_PRESERVING is cleared */
> +		stat->case_info = statx_case_ascii;

FAT is using code pages specified on the command line for it's case
insensitivity handling, which coverse much more than ASCISS.

> +/* Values stored in the low-order byte of .case_info */
> +enum {
> +	statx_case_sensitive = 0,
> +	statx_case_ascii,
> +	statx_case_utf8,
> +	statx_case_utf16,
> +};

What are these supposed to mean?  ASCII, utf8 and utf16 are all
encodings and not case folding algorithms.  While the folding is obvious
for ASCII, it is not for unicode and there are all kinds of different
variants.  Also I don't know of any file systems using utf16 encoding
and even if it did, it would interact with the VFS and nfsd using
utf8.  Note that the 16-bit ucs-2 encoding used by windows file systems
is a different things than unicode encodings like utf16.