epoll: add support for polling on epoll file descriptors

Closes ##1192.

src/unix/poll.c

@@ -63,6 +63,7 @@ struct epoll {
     struct list blocked_head;   /* an epoll_blocked per thread (in epoll_wait)  */
     struct refcount refcount;
     enum epoll_type epoll_type;
+    closure_struct(fdesc_events, fd_events);
     closure_struct(fdesc_close, close);
     closure_struct(thunk, free);
     heap h;
@@ -285,6 +286,30 @@ void epoll_finish(epoll e)
     refcount_release(&e->refcount);
 }
 
+closure_func_basic(fdesc_events, u32, epoll_events,
+                   thread t)
+{
+    epoll e = struct_from_closure(epoll, fd_events);
+    u32 events = 0;
+    spin_rlock(&e->fds_lock);
+    bitmap_foreach_set(e->fds, fd) {
+        epollfd efd = vector_get(e->events, fd);
+        if (efd->zombie)
+            continue;
+        spin_lock(&efd->lock);
+        if (efd->registered) {
+            fdesc f = efd->f;
+            events = apply(f->events, t) & (efd->eventmask | POLL_EXCEPTIONS);
+            events = report_from_notify_events(efd, events);
+        }
+        spin_unlock(&efd->lock);
+        if (events)
+            break;
+    }
+    spin_runlock(&e->fds_lock);
+    return events ? EPOLLIN : 0;
+}
+
 closure_func_basic(fdesc_close, sysreturn, epoll_close,
                    context ctx, io_completion completion)
 {
@@ -301,6 +326,7 @@ sysreturn epoll_create(int flags)
     if (e == INVALID_ADDRESS)
         return -ENOMEM;
     init_fdesc(e->h, &e->f, FDESC_TYPE_EPOLL);
+    e->f.events = init_closure_func(&e->fd_events, fdesc_events, epoll_events);
     e->f.close = init_closure_func(&e->close, fdesc_close, epoll_close);
     u64 fd = allocate_fd(current->p, e);
     if (fd == INVALID_PHYSICAL) {
@@ -633,7 +659,6 @@ sysreturn epoll_ctl(int epfd, int op, int fd, struct epoll_event *event)
     if (rv)
         return rv;
 
-    /* XXX verify that fd is not an epoll instance*/
     epoll e = resolve_fd(current->p, epfd);
     if ((e->f.type != FDESC_TYPE_EPOLL) || (f == &e->f)) {
         rv = -EINVAL;

test/runtime/epoll.c

@@ -7,6 +7,7 @@
 #include <sys/socket.h>
 #include <sys/eventfd.h>
 #include <errno.h>
+#include <poll.h>
 
 #include "../test_utils.h"
 
@@ -312,13 +313,75 @@ static void test_epollexclusive(void)
     close(evfd);
 }
 
+static void test_poll_nested(void)
+{
+    int sock_fd, polled_efd, efd;
+    struct pollfd pfd;
+    fd_set rfds, wfds, efds;
+    struct timeval tv;
+    struct epoll_event event;
+
+    polled_efd = epoll_create1(0);
+    if (polled_efd < 0)
+        test_perror("epoll_create1");
+    efd = epoll_create1(0);
+    if (efd < 0)
+        test_perror("epoll_create1");
+    event.events = EPOLLIN | EPOLLOUT;
+    event.data.fd = polled_efd;
+    test_assert(epoll_ctl(efd, EPOLL_CTL_ADD, polled_efd, &event) == 0);
+
+    /* try to put an epoll file descriptor into its own file descriptor set */
+    test_assert((epoll_ctl(efd, EPOLL_CTL_ADD, efd, &event) == -1) && (errno == EINVAL));
+
+    /* polled_efd not is not ready for I/O */
+    pfd.fd = polled_efd;
+    pfd.events = POLLIN | POLLOUT;
+    test_assert(poll(&pfd, 1, 0) == 0);
+    FD_ZERO(&rfds);
+    FD_SET(polled_efd, &rfds);
+    FD_ZERO(&wfds);
+    FD_SET(polled_efd, &wfds);
+    FD_ZERO(&efds);
+    FD_SET(polled_efd, &wfds);
+    tv.tv_sec = tv.tv_usec = 0;
+    test_assert(select(polled_efd + 1, &rfds, &wfds, &efds, &tv) == 0);
+    event.events = EPOLLIN | EPOLLOUT;
+    test_assert(epoll_wait(efd, &event, 1, 0) == 0);
+
+    /* add a socket file descriptor to polled_efd to make it ready for I/O */
+    sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
+    if (sock_fd < 0)
+        test_perror("socket");
+    event.events = EPOLLIN | EPOLLOUT;
+    test_assert(epoll_ctl(polled_efd, EPOLL_CTL_ADD, sock_fd, &event) == 0);
+
+    /* polled_efd is ready for I/O */
+    test_assert((poll(&pfd, 1, 0) == 1) && (pfd.revents == POLLIN));
+    FD_ZERO(&rfds);
+    FD_SET(polled_efd, &rfds);
+    FD_ZERO(&wfds);
+    FD_SET(polled_efd, &wfds);
+    FD_ZERO(&efds);
+    FD_SET(polled_efd, &wfds);
+    test_assert(select(polled_efd + 1, &rfds, &wfds, &efds, &tv) == 1);
+    test_assert(FD_ISSET(polled_efd, &rfds));
+    test_assert(epoll_wait(efd, &event, 1, 0) == 1);
+    test_assert((event.data.fd == polled_efd) && (event.events == EPOLLIN));
+
+    close(efd);
+    close(polled_efd);
+    close(sock_fd);
+}
+
 int main(int argc, char **argv)
 {
     test_ctl();
     test_wait();
     test_edgetrigger();
     test_eventfd_et();
     test_epollexclusive();
+    test_poll_nested();
 
     printf("test passed\n");
     return EXIT_SUCCESS;