Switch from a rake-based build to a make-based build.

This commit beefs up the Makefile to do the build, instead of the
Rakefile.

It also removes from the Rakefile the dependency on rake_utils, which
should mean it's ok to build in a schroot.

The files are reorganised to make the Makefile rules more tractable,
although the reorganisation reveals a problem with our current code
organisation.

The problem is that the proxy-specific code transitively depends on the
server code via flexnbd.h, which has a circular dependency on the server
and client structs. This should be broken in a future commit by
separating the flexnbd struct into a shared config struct and
server-specific parts, so that the server code can be moved into
src/server to more accurately show the functional dependencies.

src/common/sockutil.h

@@ -0,0 +1,41 @@
+#ifndef SOCKUTIL_H
+
+#define SOCKUTIL_H
+
+#include <sys/time.h>
+#include <sys/socket.h>
+#include <sys/select.h>
+
+/* Returns the size of the sockaddr, or 0 on error */
+size_t sockaddr_size(const struct sockaddr* sa);
+
+/* Convert a sockaddr into an address. Like inet_ntop, it returns dest if
+ * successful, NULL otherwise. In the latter case, dest will contain "???"
+ */
+const char* sockaddr_address_string(const struct sockaddr* sa, char* dest, size_t len);
+
+/* Set the SOL_REUSEADDR otion */
+int sock_set_reuseaddr(int fd, int optval);
+
+/* Set the tcp_nodelay option */
+int sock_set_tcp_nodelay(int fd, int optval);
+
+/* TODO: Set the tcp_cork option */
+// int sock_set_cork(int fd, int optval);
+
+int sock_set_nonblock(int fd, int optval);
+
+/* Attempt to bind the fd to the sockaddr, retrying common transient failures */
+int sock_try_bind(int fd, const struct sockaddr* sa);
+
+/* Try to call select(), retrying EINTR */
+int sock_try_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
+
+/* Try to call connect(), timing out after wait seconds */
+int sock_try_connect( int fd, struct sockaddr* to, socklen_t addrlen, int wait );
+
+/* Try to call close(), retrying EINTR */
+int sock_try_close( int fd );
+
+#endif
+