Re: [PATCH 7/9] blk-crypto: handle the fallback above the block layer

[Christoph Hellwig <hch@lst.de>]

On Thu, Nov 06, 2025 at 08:42:13PM -0800, Eric Biggers wrote:
> So, the new model is that if you have a bio that might have a
> bio_crypt_ctx, you always have to use blk_crypto_submit_bio() instead of
> submit_bio()?

In general yes.

> 
> It looks like usually yes, but not always, because submit_bio() still
> works with hardware inline encryption.

It has to, as that is the interface into the block layer that is used
by blk_crypto_submit_bio.  But the intent is that all submissions go
through blk_crypto_submit_bio first.

> However, it also skips the
> bio_crypt_check_alignment() check that was done before; now it happens
> only in __blk_crypto_submit_bio().  So that creates an ambiguity about
> whether that usage is allowed (if, hypothetically, a caller doesn't need
> blk-crypto-fallback support).
> 
> Maybe the alignment check should be done both in submit_bio_noacct()
> after verifying blk_crypto_config_supported_natively(), and in
> __blk_crypto_submit_bio() after deciding to use the fallback?  Those
> cases are exclusive, so the check would still happen just once per bio.

We could do that.  Or I lift the checking into the core bio splitting
code at least for the hardware case to reduce the overhead.  I'll see
what works out better.

> Either way, the kerneldoc needs to be improved to accurately document
> what blk_crypto_submit_bio() does, when it should be called, and how it
> differs from submit_bio().  This also deserves a mention in the "API
> presented to users of the block layer" section of
> Documentation/block/inline-encryption.rst.

Ok.