Re: [PATCH v2 04/17] fscrypt: Fully disallow IV_INO_LBLK_32 with s_blocksize != PAGE_SIZE

On Sun, Jul 05, 2026 at 12:45:41PM -0700, Eric Biggers wrote:
> FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32 with s_blocksize != PAGE_SIZE works
> only with the fs-layer implementation of file contents encryption, not
> blk-crypto.  This is a problem for standardizing on blk-crypto.
> 
> Fortunately, no one should be using this combination anyway.  It doesn't
> make sense because the entire point of IV_INO_LBLK_32 is to support
> inline encryption hardware that is limited to 32-bit DUNs.
> 
> Thus, fully disallow IV_INO_LBLK_32 with s_blocksize != PAGE_SIZE.
> 
> Reviewed-by: Christoph Hellwig <[email protected]>
> Signed-off-by: Eric Biggers <[email protected]>

Sashiko doesn't like that this would break compatibility of existing
directories using FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32 if someone updates
their kernel to use a different page size.  I think we'll just have to
take the risk here.  I'm pretty confident this scenario isn't being
relied on in practice, for various reasons including the one mentioned.

- Eric