io: allow overriding poll function.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/io/backend.h

@@ -2,7 +2,6 @@
 #ifndef CCAN_IO_BACKEND_H
 #define CCAN_IO_BACKEND_H
 #include <stdbool.h>
-#include <poll.h>
 #include "io_plan.h"
 #include <ccan/list/list.h>
 

ccan/io/io.h

@@ -4,6 +4,7 @@
 #include <ccan/tal/tal.h>
 #include <ccan/typesafe_cb/typesafe_cb.h>
 #include <stdbool.h>
+#include <poll.h>
 #include <unistd.h>
 
 struct timers;
@@ -701,4 +702,14 @@ bool io_flush_sync(struct io_conn *conn);
  */
 struct timemono (*io_time_override(struct timemono (*now)(void)))(void);
 
+/**
+ * io_poll_override - override the normal call for poll.
+ * @pollfn: the function to call.
+ *
+ * io usually uses poll() internally, but this forces it to use your
+ * function (eg. for debugging, suppressing fds, or polling on others unknown
+ * to ccan/io).  Returns the old one.
+ */
+int (*io_poll_override(int (*poll)(struct pollfd *fds, nfds_t nfds, int timeout)))(struct pollfd *, nfds_t, int);
+
 #endif /* CCAN_IO_H */

ccan/io/poll.c

@@ -17,6 +17,7 @@ static struct fd **fds = NULL;
 static LIST_HEAD(closing);
 static LIST_HEAD(always);
 static struct timemono (*nowfn)(void) = time_mono;
+static int (*pollfn)(struct pollfd *fds, nfds_t nfds, int timeout) = poll;
 
 struct timemono (*io_time_override(struct timemono (*now)(void)))(void)
 {
@@ -25,6 +26,13 @@ struct timemono (*io_time_override(struct timemono (*now)(void)))(void)
 	return old;
 }
 
+int (*io_poll_override(int (*poll)(struct pollfd *fds, nfds_t nfds, int timeout)))(struct pollfd *, nfds_t, int)
+{
+	int (*old)(struct pollfd *fds, nfds_t nfds, int timeout) = pollfn;
+	pollfn = poll;
+	return old;
+}
+
 static bool add_fd(struct fd *fd, short events)
 {
 	if (!max_fds) {
@@ -269,7 +277,7 @@ void *io_loop(struct timers *timers, struct timer **expired)
 			}
 		}
 
-		r = poll(pollfds, num_fds, ms_timeout);
+		r = pollfn(pollfds, num_fds, ms_timeout);
 		if (r < 0)
 			break;
 

ccan/io/test/run-41-io_poll_override.c

@@ -0,0 +1,57 @@
+#include <ccan/io/io.h>
+/* Include the C files directly. */
+#include <ccan/io/poll.c>
+#include <ccan/io/io.c>
+#include <ccan/tap/tap.h>
+#include <sys/wait.h>
+#include <stdio.h>
+
+#define PORT "65020"
+
+/* Should be looking to read from one fd. */
+static int mypoll(struct pollfd *fds, nfds_t nfds, int timeout)
+{
+	ok1(nfds == 1);
+	ok1(fds[0].fd >= 0);
+	ok1(fds[0].events & POLLIN);
+	ok1(!(fds[0].events & POLLOUT));
+
+	/* Pretend it's readable. */
+	fds[0].revents = POLLIN;
+	return 1;
+}
+
+static int check_cant_read(int fd, struct io_plan_arg *arg)
+{
+	char c;
+	ssize_t ret = read(fd, &c, 1);
+
+	ok1(errno == EAGAIN || errno == EWOULDBLOCK);
+	ok1(ret == -1);
+
+	return 1;
+}
+
+static struct io_plan *setup_conn(struct io_conn *conn, void *unused)
+{
+	/* Need to get this to mark it IO_POLLING */
+	io_plan_arg(conn, IO_IN);
+	return io_set_plan(conn, IO_IN, check_cant_read, io_close_cb, NULL);
+}
+
+int main(void)
+{
+	int fds[2];
+
+	plan_tests(8);
+
+	pipe(fds);
+	ok1(io_poll_override(mypoll) == poll);
+
+	io_new_conn(NULL, fds[0], setup_conn, NULL);
+	ok1(io_loop(NULL, NULL) == NULL);
+	close(fds[1]);
+
+	/* This exits depending on whether all tests passed */
+	return exit_status();
+}