dropping the non-inline mode for fscrypt?

[Christoph Hellwig <hch@lst.de>]

After just having run into another issue with missing testing for one of
the path, I'd like to ask if we should look into dropping the non-inline
mode for block based fscrypt?

I did a few simple fio based benchmarks, and writes are a minimal amount
fast for the inline mode, while the reverse is true for reads.

The big blocker seems to be this comment in fscrypt_select_encryption_impl:

        /*
         * When a page contains multiple logically contiguous filesystem blocks,
         * some filesystem code only calls fscrypt_mergeable_bio() for the first
         * block in the page. This is fine for most of fscrypt's IV generation
         * strategies, where contiguous blocks imply contiguous IVs. But it
         * doesn't work with IV_INO_LBLK_32. For now, simply exclude
         * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
         */

from touching the file system callers lately, the only obvious place
for this is fscrypt_zeroout_range_inline_crypt helper, or did I miss
anything else?  Does anyone have a good xfstests setup for the
IV_INO_LBLK_32 mode?