Use timerfd for timeout handling

Use a new file descriptor from the timerfd system calls to handle
timeouts. On supported systems, this means that there is less hassle
figuring out when the poll() timeout should be, since
libusb_get_next_timeout() will always return 0 and the timeout events will
be triggered as regular activity on the file descriptor set.

Add API function libusb_pollfds_handle_timeouts() to detect whether
you're on a platform with the timing headache, and flesh out the
surrounding documentation.

1 files changed, 35 insertions, 46 deletions

diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
index cf30703..ffa4088 100644
--- a/libusb/os/linux_usbfs.c
+++ b/libusb/os/linux_usbfs.c
@@ -187,36 +187,22 @@ static const char *find_usbfs_path(void)
 	return ret;
 }
 
+/* the monotonic clock is not usable on all systems (e.g. embedded ones often
+ * seem to lack it). fall back to REALTIME if we have to. */
 static clockid_t find_monotonic_clock(void)
 {
 	struct timespec ts;
-	int i;
-	const clockid_t clktypes[] = {
-		/* the most monotonic clock I know about, but only available since
-		 * Linux 2.6.28, and not even available in glibc-2.10 */
-#ifndef CLOCK_MONOTONIC_RAW
-#define CLOCK_MONOTONIC_RAW 4
-#endif
-		CLOCK_MONOTONIC_RAW,
-
-		/* a monotonic clock, but it's not available on all architectures,
-		 * and is susceptible to ntp adjustments */
-		CLOCK_MONOTONIC,
-
-		/* the fallback option */
-		CLOCK_REALTIME,
-	};
+	int r;
 
-	for (i = 0; i < (sizeof(clktypes) / sizeof(*clktypes)); i++) {
-		int r = clock_gettime(clktypes[i], &ts);
-		if (r == 0) {
-			usbi_dbg("clock %d selected", clktypes[i]);
-			return r;
-		}
-		usbi_dbg("clock %d doesn't work", clktypes[i]);
+	/* Linux 2.6.28 adds CLOCK_MONOTONIC_RAW but we don't use it
+	 * because it's not available through timerfd */
+	r = clock_gettime(CLOCK_MONOTONIC, &ts);
+	if (r == 0) {
+		return CLOCK_MONOTONIC;
+	} else {
+		usbi_dbg("monotonic clock doesn't work, errno %d", errno);
+		return CLOCK_REALTIME;
 	}
-
-	return -1;
 }
 
 /* bulk continuation URB flag available from Linux 2.6.32 */
@@ -247,13 +233,8 @@ static int op_init(struct libusb_context *ctx)
 		return LIBUSB_ERROR_OTHER;
 	}
 
-	if (monotonic_clkid == -1) {
+	if (monotonic_clkid == -1)
 		monotonic_clkid = find_monotonic_clock();
-		if (monotonic_clkid == -1) {
-			usbi_err(ctx, "could not find working monotonic clock");
-			return LIBUSB_ERROR_OTHER;
-		}
-	}
 
 	if (supports_flag_bulk_continuation == -1) {
 		supports_flag_bulk_continuation = check_flag_bulk_continuation();
@@ -1792,6 +1773,7 @@ static int handle_bulk_completion(struct usbi_transfer *itransfer,
 	int num_urbs = tpriv->num_urbs;
 	int urb_idx = urb - tpriv->urbs;
 	enum libusb_transfer_status status = LIBUSB_TRANSFER_COMPLETED;
+	int r = 0;
 
 	pthread_mutex_lock(&itransfer->lock);
 	usbi_dbg("handling completion status %d of bulk urb %d/%d", urb->status,
@@ -1838,7 +1820,7 @@ static int handle_bulk_completion(struct usbi_transfer *itransfer,
 				free(tpriv->urbs);
 				tpriv->urbs = NULL;
 				pthread_mutex_unlock(&itransfer->lock);
-				usbi_handle_transfer_cancellation(itransfer);
+				r = usbi_handle_transfer_cancellation(itransfer);
 				goto out_unlock;
 			}
 			if (tpriv->reap_action != COMPLETED_EARLY)
@@ -1902,8 +1884,8 @@ static int handle_bulk_completion(struct usbi_transfer *itransfer,
 			 * cancelled by the kernel */
 			if (tpriv->urbs[i].flags & USBFS_URB_BULK_CONTINUATION)
 				continue;
-			int r = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, &tpriv->urbs[i]);
-			if (r && errno != EINVAL)
+			int tmp = ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, &tpriv->urbs[i]);
+			if (tmp && errno != EINVAL)
 				usbi_warn(TRANSFER_CTX(transfer),
 					"unrecognised discard errno %d", errno);
 		}
@@ -1916,11 +1898,10 @@ completed:
 	free(tpriv->urbs);
 	tpriv->urbs = NULL;
 	pthread_mutex_unlock(&itransfer->lock);
-	usbi_handle_transfer_completion(itransfer, status);
-	return 0;
+	return usbi_handle_transfer_completion(itransfer, status);
 out_unlock:
 	pthread_mutex_unlock(&itransfer->lock);
-	return 0;
+	return r;
 }
 
 static int handle_iso_completion(struct usbi_transfer *itransfer,
@@ -1971,13 +1952,12 @@ static int handle_iso_completion(struct usbi_transfer *itransfer,
 			free_iso_urbs(tpriv);
 			if (tpriv->reap_action == CANCELLED) {
 				pthread_mutex_unlock(&itransfer->lock);
-				usbi_handle_transfer_cancellation(itransfer);
+				return usbi_handle_transfer_cancellation(itransfer);
 			} else {
 				pthread_mutex_unlock(&itransfer->lock);
-				usbi_handle_transfer_completion(itransfer,
+				return usbi_handle_transfer_completion(itransfer,
 					LIBUSB_TRANSFER_ERROR);
 			}
-			return 0;
 		}
 		goto out;
 	}
@@ -2002,8 +1982,7 @@ static int handle_iso_completion(struct usbi_transfer *itransfer,
 		usbi_dbg("last URB in transfer --> complete!");
 		free_iso_urbs(tpriv);
 		pthread_mutex_unlock(&itransfer->lock);
-		usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
-		return 0;
+		return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
 	}
 
 out:
@@ -2030,8 +2009,7 @@ static int handle_control_completion(struct usbi_transfer *itransfer,
 		free(tpriv->urbs);
 		tpriv->urbs = NULL;
 		pthread_mutex_unlock(&itransfer->lock);
-		usbi_handle_transfer_cancellation(itransfer);
-		return 0;
+		return usbi_handle_transfer_cancellation(itransfer);
 	}
 
 	switch (urb->status) {
@@ -2059,8 +2037,7 @@ static int handle_control_completion(struct usbi_transfer *itransfer,
 	free(tpriv->urbs);
 	tpriv->urbs = NULL;
 	pthread_mutex_unlock(&itransfer->lock);
-	usbi_handle_transfer_completion(itransfer, status);
-	return 0;
+	return usbi_handle_transfer_completion(itransfer, status);
 }
 
 static int reap_for_handle(struct libusb_device_handle *handle)
@@ -2157,6 +2134,14 @@ static int op_clock_gettime(int clk_id, struct timespec *tp)
   }
 }
 
+#ifdef USBI_TIMERFD_AVAILABLE
+static clockid_t op_get_timerfd_clockid(void)
+{
+	return monotonic_clkid;
+
+}
+#endif
+
 const struct usbi_os_backend linux_usbfs_backend = {
 	.name = "Linux usbfs",
 	.init = op_init,
@@ -2191,6 +2176,10 @@ const struct usbi_os_backend linux_usbfs_backend = {
 
 	.clock_gettime = op_clock_gettime,
 
+#ifdef USBI_TIMERFD_AVAILABLE
+	.get_timerfd_clockid = op_get_timerfd_clockid,
+#endif
+
 	.device_priv_size = sizeof(struct linux_device_priv),
 	.device_handle_priv_size = sizeof(struct linux_device_handle_priv),
 	.transfer_priv_size = sizeof(struct linux_transfer_priv),