[openssl-dev] AF_ALG engine support and kernel versions

[Jeffrey Walton]

> Looking at the code in engines/afalg/e_afalg.c, there is the following:
>
>   ...
>   #define K_MAJ   4
>   #define K_MIN1  1
>   #define K_MIN2  0
>   #if LINUX_VERSION_CODE <= KERNEL_VERSION(K_MAJ, K_MIN1, K_MIN2)
>   # warning "AFALG ENGINE requires Kernel Headers >= 4.1.0"
>   # warning "Skipping Compilation of AFALG engine"
>   #else
>   ...
>
> It appears AF_ALG was added to the kernel at 2.6.38. Asynchronous I/O
> support appears to have surfaced in the kernel at 2.5.23.
>
> Where is the requirement for 4.1 coming from?
>
> Also, "Fixing asynchronous I/O, again", dated January 2016
> (http://lwn.net/Articles/671649/) could explain why later 4.x kernels
> are having problems with the afalgtest.

I think this has to do with the asynchronous cipher support. Its just
a guess because I can't seem to find any information on it. CHANGES
talks about "ASYNC support" between 1.0.2 and 1.1.1, but it does not
discuss AF_ALG.

Its not clear to me were the supporting kernel versions begin or end.
It appears asynchronous cipher stuff is still being cut-in. This
meesage is from two weeks ago: "[PATCH v3] crypto: af_alg - add async
support to algif_aead",
http://marc.info/?l=linux-crypto-vger&m=145772613405482.

Jeff