[sheepdog] [PATCH v3 3/8] sheep, sockfd cache: cache more than one FD for each node

[Christoph Hellwig]

On Tue, Jun 26, 2012 at 04:45:39PM +0800, Liu Yuan wrote:
> From: Liu Yuan <tailai.ly at taobao.com>
> 
> This is inspired by the observation that each Guest can issue as much
> as 4 requests in one go.
> 
> The complexity added to the code is seen outside of sockfd cache:
> add one more parameter to the API: FD index. The underlying core needs this to
> identify which FD belongs one node is actually used.
> 
> I think this trade-off is a good deal.

I think so to.

> -		fd = sheep_get_fd(v);
> +		fd = sheep_get_fd(v, &sock_idx);
>  		if (fd < 0) {

> +			sheep_del_fd(v, fd, sock_idx);

I think APIs that expect to be passed multiple related but not grouped
arguments are a desaster waiting to happen.

I'd probably pass what's the struct write_info_ent I suggested in the
last patch here.  While the pfd argument isn't need for reads I'd
rather trade a little more stack usage for a much more coherent
interface.

Also I suspect instead of just returning the index I'd suggest returning
the actual pointer to the sockfd_cache_entry as well, to avoid having
to do another lookup and lock roundtrip when dropping the reference.