[PATCH v9 2/4] fs: Add standard casefolding support

[Eric Biggers]

On Tue, Jun 23, 2020 at 09:33:39PM -0700, Daniel Rosenberg wrote:
> This adds general supporting functions for filesystems that use
> utf8 casefolding. It provides standard dentry_operations and adds the
> necessary structures in struct super_block to allow this standardization.
> 
> Ext4 and F2fs will switch to these common implementations.

It would be helpful to explicitly call out anything that's "new" in this commit,
i.e. anything that isn't simply moving code into the libfs with no behavior
changes.  There's the change of ->d_hash() to use utf8_casefold_hash() instead
of allocating memory; that's not present in the ext4 and f2fs versions.

There's also the change of needs_casefold() to be aware of encrypt+casefold.
(Maybe that small change would better belong in a later patchset that actually
introduces encrypt+casefold support?)

Anything else?

> +/**
> + * generic_ci_d_hash - generic d_hash implementation for casefolding filesystems
> + * @dentry:	dentry whose name we are hashing
> + * @str:	qstr of name whose hash we should fill in
> + *
> + * Return: 0 if hash was successful, or -ERRNO
> + */

It also returns 0 if the hashing was not done because it wants to fallback to
the standard hashing.

> +static inline bool needs_casefold(const struct inode *dir)
> +{
> +	return 0;
> +}

The return type is bool, so it should 'return false', not 'return 0'.

- Eric