Question on __crypto_alg_lookup

Folks:

In __crypto_alg_lookup, at about line 85 of api.c, there is the following:

                 if ((q->cra_flags ^ type) & mask)
                         continue;

There is no commenting on this at all.

Can someone please explain what this is for and just what is this trying
to filter?

I am trying to get dm-crypt to work with a ahash device that we have.

The dm-crypt is calling crypto_alloc_hash with "sha256" type 0, and 
mask 0x 80

My driver is setting these flags:

                 .cra_flags              = CRYPTO_ALG_TYPE_AHASH |
                                                 CRYPTO_ALG_ASYNC,

The search seems to be failing at the above sequence in 
__crypto_alg_lookup.

Is dm-crypt supposed to work with ahash?

The Documentation/crypto does not seem to include much information
on using the ahash and ablkcipher infrastructure.

There is one document called async-tx-api.txt that seems to have no
correlation with the ahash or ablkcipher stuff. Is it still valid?

Is there another place I can look for decent documentation?

Thank you

Truly,

Mark Allyn
Portland, Oregon
www.allyn.com
971-563-7588