[PATCH 3/4] Add write buffer queue for non-blocking write

[Denis Kenzior]

Hi Zhenhua,

> The head of the queue is the data to be written, the tail is the
> free buffer to cache data into.
> 
> If the tail of queue is full, allocate a new free buffer and
> append it at the tail.

Patch has been applied with one minor tweak afterwards.

Thanks,
-Denis