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

[Daniel Rosenberg]

On Tue, Jun 23, 2020 at 10:57 PM Eric Biggers <ebiggers at kernel.org> wrote:
>
> Note that the '!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir)' check can
> be racy, because a process can be looking up a no-key token in a directory while
> concurrently another process initializes the directory's ->i_crypt_info, causing
> fscrypt_has_encryption_key(dir) to suddenly start returning true.
>
> In my rework of filename handling in f2fs, I actually ended up removing all
> calls to needs_casefold(), thus avoiding this race.  f2fs now decides whether
> the name is going to need casefolding early on, in __f2fs_setup_filename(),
> where it knows in a race-free way whether the filename is a no-key token or not.
>
> Perhaps ext4 should work the same way?  It did look like there would be some
> extra complexity due to how the ext4 directory hashing works in comparison to
> f2fs's, but I haven't had a chance to properly investigate it.
>
> - Eric

Hm. I think I should be able to just check for DCACHE_ENCRYPTED_NAME
in the dentry here, right? I'm just trying to avoid casefolding the
no-key token, and that flag should indicate that.
I'll see if I can rework the ext4 patches to not need needs_casefold
as well, since then there'd be no need to export it.
-Daniel