Re: [LTP] [LTP PATCH 0/2] ltp: fix af_alg02 to specify control data

Hi Eric,

It isn't clearly defined what happens if you read from an AF_ALG request
socket without previously sending the control data to begin an
encryption or decryption operation.  On some kernels the read will
return 0, while on others it will block.

Testing this corner case isn't the purpose of af_alg02; it just wants to
try to encrypt a zero-length message.  So, change it to explicitly send
a zero-length message with control data.

This fixes the test failure reported at
https://lkml.kernel.org/r/CA+G9fYtebf78TH-XpqArunHc1L6s9mHdLEbpY1EY9tSyDjp=sg@mail.gmail.com

Fixing the test in this way was also previously suggested at
https://lkml.kernel.org/r/20200702033221.GA19367@gondor.apana.org.au

Note, this patch doesn't change the fact that the read() still blocks on
pre-4.14 kernels (which is a kernel bug), and thus the timeout logic in
the test is still needed.

Thanks for the fix, merged!

Kind regards,
Petr