Due to scheduling, the client could attempt to connect to the server
before the server starts to accept. Make the client retry multiple
times before returning with error.
It is slow to allocate big buffers using SGX SDK's malloc. Even worse, it
consumes a large amount of precious trusted memory inside enclaves. This
commit avoids using trusted buffers and allocates untrusted buffers for
sendmsg/recvmsg directly via OCall, thus improving the performance of
sendmsg/recvmsg. Note that this optimization does not affect the security of
network data as it has to be sent/received via OCalls.
1. Add a separate net/ directory for the network subsystem;
2. Move some existing socket code to net/;
3. Implement sendmsg/recvmsg with OCalls;
4. Extend client/server test cases.
1. Change the port for server_poll to listen to avoid "address in use" conflict
between test/server and test/server_epoll, and add port as an argument for
test/client to send message
2. As posix-spwan may fail, change the fixed number of processes to spawn to
the number of processes successfully spawned in server_epoll
