SR-4026: dispatch_test_check_evfilt_read_for_fd for epoll

Implement dispatch_test_check_evfilt_read_for_fd test method
for the event_epoll backend.

Author: dgrove-oss

tests/dispatch_test.c

@@ -31,6 +31,9 @@
 #if __has_include(<sys/event.h>)
 #define HAS_SYS_EVENT_H 1
 #include <sys/event.h>
+#else
+#include <sys/epoll.h>
+#include <sys/eventfd.h>
 #endif
 #include <assert.h>
 
@@ -65,8 +68,39 @@ dispatch_test_check_evfilt_read_for_fd(int fd)
 	close(kq);
 	return r > 0;
 #else
-	// TODO: Need to write a real check for epoll-backend here
-	return true;
+	struct stat sb;
+	struct epoll_event ev, events[1];
+	int epollfd, numReady, r;
+	int dummyfd = -1;
+
+	if (fstat(fd, &sb) < 0) {
+		return false;
+	}
+
+	epollfd = epoll_create1(0);
+	assert(epollfd != -1);
+
+	if (S_ISREG(sb.st_mode)) {
+		dummyfd = eventfd(1, EFD_CLOEXEC | EFD_NONBLOCK); // dummy eventfd that is always readable
+		fd = dummyfd;
+	}
+
+	ev.events = EPOLLIN;
+	ev.data.fd = fd;
+	r = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev);
+	assert(r != -1);
+
+	numReady = epoll_wait(epollfd, events, 1, 0);
+	assert(numReady != -1);
+
+	r = close(epollfd);
+	assert(r != -1);
+	if (dummyfd != -1) {
+		r = close(dummyfd);
+		assert(r != -1);
+	}
+
+	return numReady > 0;
 #endif
 }