shared: move nm_utils_fd_*() from src/ to shared/nm-utils/

The functions are general purpose and independent from NetworkManager core.
Move them to "shared/nm-utils/" so they can be used independently.

shared/nm-utils/nm-shared-utils.c

@@ -25,6 +25,7 @@
 
 #include <errno.h>
 #include <arpa/inet.h>
+#include <poll.h>
 
 /*****************************************************************************/
 
@@ -992,3 +993,99 @@ nm_utils_str_utf8safe_escape_take (char *str, NMUtilsStrUtf8SafeFlags flags)
 	}
 	return str;
 }
+
+/*****************************************************************************/
+
+/* taken from systemd's fd_wait_for_event(). Note that the timeout
+ * is here in nano-seconds, not micro-seconds. */
+int
+nm_utils_fd_wait_for_event (int fd, int event, gint64 timeout_ns)
+{
+	struct pollfd pollfd = {
+		.fd = fd,
+		.events = event,
+	};
+	struct timespec ts, *pts;
+	int r;
+
+	if (timeout_ns < 0)
+		pts = NULL;
+	else {
+		ts.tv_sec = (time_t) (timeout_ns / NM_UTILS_NS_PER_SECOND);
+		ts.tv_nsec = (long int) (timeout_ns % NM_UTILS_NS_PER_SECOND);
+		pts = &ts;
+	}
+
+	r = ppoll (&pollfd, 1, pts, NULL);
+	if (r < 0)
+		return -errno;
+	if (r == 0)
+		return 0;
+	return pollfd.revents;
+}
+
+/* taken from systemd's loop_read() */
+ssize_t
+nm_utils_fd_read_loop (int fd, void *buf, size_t nbytes, bool do_poll)
+{
+	uint8_t *p = buf;
+	ssize_t n = 0;
+
+	g_return_val_if_fail (fd >= 0, -EINVAL);
+	g_return_val_if_fail (buf, -EINVAL);
+
+	/* If called with nbytes == 0, let's call read() at least
+	 * once, to validate the operation */
+
+	if (nbytes > (size_t) SSIZE_MAX)
+		return -EINVAL;
+
+	do {
+		ssize_t k;
+
+		k = read (fd, p, nbytes);
+		if (k < 0) {
+			if (errno == EINTR)
+				continue;
+
+			if (errno == EAGAIN && do_poll) {
+
+				/* We knowingly ignore any return value here,
+				 * and expect that any error/EOF is reported
+				 * via read() */
+
+				(void) nm_utils_fd_wait_for_event (fd, POLLIN, -1);
+				continue;
+			}
+
+			return n > 0 ? n : -errno;
+		}
+
+		if (k == 0)
+			return n;
+
+		g_assert ((size_t) k <= nbytes);
+
+		p += k;
+		nbytes -= k;
+		n += k;
+	} while (nbytes > 0);
+
+	return n;
+}
+
+/* taken from systemd's loop_read_exact() */
+int
+nm_utils_fd_read_loop_exact (int fd, void *buf, size_t nbytes, bool do_poll)
+{
+	ssize_t n;
+
+	n = nm_utils_fd_read_loop (fd, buf, nbytes, do_poll);
+	if (n < 0)
+		return (int) n;
+	if ((size_t) n != nbytes)
+		return -EIO;
+
+	return 0;
+}
+