implement POSIX shared memory

src/mman/shm_open.c

+#include <sys/mman.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+int shm_open(const char *name, int flag, mode_t mode)
+{
+	int fd, dir;
+
+	while (*name == '/') name++;
+	if (strchr(name, '/')) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if ((dir = open("/dev/shm", O_DIRECTORY|O_RDONLY)) < 0) return -1;
+	fd = openat(dir, name, flag|O_NOFOLLOW|O_CLOEXEC|O_NONBLOCK, mode);
+	close(dir);
+	return fd;
+}

src/mman/shm_unlink.c

+#include <sys/mman.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+int shm_unlink(const char *name)
+{
+	int dir, ret;
+
+	while (*name == '/') name++;
+	if (strchr(name, '/')) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if ((dir = open("/dev/shm", O_DIRECTORY|O_RDONLY)) < 0) return -1;
+	ret = unlinkat(dir, name, 0);
+	close(dir);
+	return ret;
+}