samples: posix: eventfd: Sample application for eventfd() call.

Roughly based on eventfd example code from Linux manpages. Similarly
to other POSIX-compatible sample, Makefile.posix is provided to build
the code on a POSIX system (in this case, as eventfd() is
Linux-specific, this has to be a Linux system).

Signed-off-by: Paul Sokolovsky <[email protected]>

Author: pfalcon

samples/posix/eventfd/CMakeLists.txt

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+
+find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
+project(eventfd)
+
+#target_include_directories(app PRIVATE ${ZEPHYR_BASE}/include/posix)
+target_sources(app PRIVATE src/main.c)

samples/posix/eventfd/Makefile.posix

@@ -0,0 +1,4 @@
+# This makefile builds the sample for a POSIX system, like Linux
+
+eventfd: src/main.c
+	$(CC) $^ -o $@

samples/posix/eventfd/prj.conf

@@ -0,0 +1,7 @@
+# General config
+CONFIG_NEWLIB_LIBC=y
+CONFIG_POSIX_API=y
+CONFIG_EVENTFD=y
+
+# Networking config
+CONFIG_NETWORKING=y

samples/posix/eventfd/src/main.c

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2020 Linaro Limited
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * This sample application is roughly based on the sample code in Linux
+ * manpage for eventfd().
+ */
+#include <sys/eventfd.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+
+#define fatal(msg) \
+	do { perror(msg); exit(EXIT_FAILURE); } while (0)
+
+/* As Zephyr doesn't provide command-line args, emulate them. */
+char *input_argv[] = {"argv0", "1", "2", "3", "4"};
+
+int efd;
+int g_argc;
+char **g_argv;
+
+void writer(void)
+{
+	int j;
+	uint64_t u;
+	ssize_t s;
+
+	for (j = 1; j < g_argc; j++) {
+		printf("Writing %s to efd\n", g_argv[j]);
+		u = strtoull(g_argv[j], NULL, 0);
+		s = write(efd, &u, sizeof(uint64_t));
+		if (s != sizeof(uint64_t)) {
+			fatal("write");
+		}
+	}
+	printf("Completed write loop\n");
+}
+
+void reader(void)
+{
+	uint64_t u;
+	ssize_t s;
+
+	sleep(1);
+
+	printf("About to read\n");
+	s = read(efd, &u, sizeof(uint64_t));
+	if (s != sizeof(uint64_t)) {
+		fatal("read");
+	}
+	printf("Read %llu (0x%llx) from efd\n",
+	       (unsigned long long)u, (unsigned long long)u);
+}
+
+int main(int argc, char *argv[])
+{
+	argv = input_argv;
+	argc = sizeof(input_argv) / sizeof(input_argv[0]);
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s <num>...\n", argv[0]);
+		exit(EXIT_FAILURE);
+	}
+
+	g_argc = argc;
+	g_argv = argv;
+
+	efd = eventfd(0, 0);
+	if (efd == -1) {
+		fatal("eventfd");
+	}
+
+	writer();
+	reader();
+
+	return 0;
+}