[PATCHSET 0.4] Reduce overhead of multishot recv/recvmsg

[Jens Axboe <axboe@kernel.dk>]

Hi,

With the way that the multishot variants of recv and recvmsg currently
work, we always end up doing two sock_recvmsg() call for each subsequent
receive outside of the initial receive. That is obviously extra overhead,
and to make matters worse, that also involves picking and recycling an
appropriate buffer for those operations.

For protocols that sanely pass back whether a socket has more data
after a receive, we can rely on that hint to avoid iterating over
recvmsg/buffers an extra time per receive.

Patches 1..3 are prep patches, patch 4 has the logic mentioned above.

-- 
Jens Axboe