X-Git-Url: https://sigrok.org/gitweb/?p=libsigrok.git;a=blobdiff_plain;f=hardware%2Fcommon%2Fserial.c;h=9a9a0d94fd3b3058e84ba74202db681de8397885;hp=342980d0053e40694f781900ee6ccfce20a4d8ff;hb=43cd4637285833706f8a404ca027bcf0ee75b9ae;hpb=c4d85a4026cd9c593521a635b1e477aac15eb86a

diff --git a/hardware/common/serial.c b/hardware/common/serial.c
index 342980d0..9a9a0d94 100644
--- a/hardware/common/serial.c
+++ b/hardware/common/serial.c
@@ -22,30 +22,25 @@
 #include <string.h>
 #include <stdlib.h>
 #include <glib.h>
+#include <glib/gstdio.h>
 #include <libserialport.h>
 #include "libsigrok.h"
 #include "libsigrok-internal.h"
 
-/* Message logging helpers with subsystem-specific prefix string. */
-#define LOG_PREFIX "serial: "
-#define sr_log(l, s, args...) sr_log(l, LOG_PREFIX s, ## args)
-#define sr_spew(s, args...) sr_spew(LOG_PREFIX s, ## args)
-#define sr_dbg(s, args...) sr_dbg(LOG_PREFIX s, ## args)
-#define sr_info(s, args...) sr_info(LOG_PREFIX s, ## args)
-#define sr_warn(s, args...) sr_warn(LOG_PREFIX s, ## args)
-#define sr_err(s, args...) sr_err(LOG_PREFIX s, ## args)
+#define LOG_PREFIX "serial"
 
 /**
  * Open the specified serial port.
  *
  * @param serial Previously initialized serial port structure.
- * @param flags Flags to use when opening the serial port. Possible flags
+ * @param[in] flags Flags to use when opening the serial port. Possible flags
  *              include SERIAL_RDWR, SERIAL_RDONLY, SERIAL_NONBLOCK.
  *
  * If the serial structure contains a serialcomm string, it will be
  * passed to serial_set_paramstr() after the port is opened.
  *
- * @return SR_OK on success, SR_ERR on failure.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_open(struct sr_serial_dev_inst *serial, int flags)
 {
@@ -66,8 +61,8 @@ SR_PRIV int serial_open(struct sr_serial_dev_inst *serial, int flags)
 		sp_flags = (SP_MODE_READ | SP_MODE_WRITE);
 	else if (flags & SERIAL_RDONLY)
 		sp_flags = SP_MODE_READ;
-	if (flags & SERIAL_NONBLOCK)
-		sp_flags |= SP_MODE_NONBLOCK;
+
+	serial->nonblocking = (flags & SERIAL_NONBLOCK) ? 1 : 0;
 
 	ret = sp_open(serial->data, sp_flags);
 
@@ -77,15 +72,12 @@ SR_PRIV int serial_open(struct sr_serial_dev_inst *serial, int flags)
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Error opening port: %s.", error);
+		sr_err("Error opening port (%d): %s.",
+			sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
 
-#ifndef _WIN32
-	sp_get_port_handle(serial->data, &serial->fd);
-#endif
-
 	if (serial->serialcomm)
 		return serial_set_paramstr(serial, serial->serialcomm);
 	else
@@ -97,7 +89,8 @@ SR_PRIV int serial_open(struct sr_serial_dev_inst *serial, int flags)
  *
  * @param serial Previously initialized serial port structure.
  *
- * @return SR_OK on success, SR_ERR on failure.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_close(struct sr_serial_dev_inst *serial)
 {
@@ -109,16 +102,14 @@ SR_PRIV int serial_close(struct sr_serial_dev_inst *serial)
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot close unopened serial port %s (fd %d).",
-				serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot close unopened serial port %s.", serial->port);
 		return SR_ERR;
 	}
 
-	sr_spew("Closing serial port %s (fd %d).", serial->port, serial->fd);
+	sr_spew("Closing serial port %s.", serial->port);
 
 	ret = sp_close(serial->data);
-	sp_free_port(serial->data);
 
 	switch (ret) {
 	case SP_ERR_ARG:
@@ -126,12 +117,14 @@ SR_PRIV int serial_close(struct sr_serial_dev_inst *serial)
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Error closing port: %s.", error);
+		sr_err("Error closing port (%d): %s.",
+			sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
 
-	serial->fd = -1;
+	sp_free_port(serial->data);
+	serial->data = NULL;
 
 	return SR_OK;
 }
@@ -141,7 +134,8 @@ SR_PRIV int serial_close(struct sr_serial_dev_inst *serial)
  *
  * @param serial Previously initialized serial port structure.
  *
- * @return SR_OK on success, SR_ERR on failure.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_flush(struct sr_serial_dev_inst *serial)
 {
@@ -153,13 +147,12 @@ SR_PRIV int serial_flush(struct sr_serial_dev_inst *serial)
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot flush unopened serial port %s (fd %d).",
-				serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot flush unopened serial port %s.", serial->port);
 		return SR_ERR;
 	}
 
-	sr_spew("Flushing serial port %s (fd %d).", serial->port, serial->fd);
+	sr_spew("Flushing serial port %s.", serial->port);
 
 	ret = sp_flush(serial->data, SP_BUF_BOTH);
 
@@ -169,7 +162,8 @@ SR_PRIV int serial_flush(struct sr_serial_dev_inst *serial)
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Error flushing port: %s.", error);
+		sr_err("Error flushing port (%d): %s.",
+			sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
@@ -177,17 +171,8 @@ SR_PRIV int serial_flush(struct sr_serial_dev_inst *serial)
 	return SR_OK;
 }
 
-/**
- * Write a number of bytes to the specified serial port.
- *
- * @param serial Previously initialized serial port structure.
- * @param buf Buffer containing the bytes to write.
- * @param count Number of bytes to write.
- *
- * @return The number of bytes written, or a negative error code upon failure.
- */
-SR_PRIV int serial_write(struct sr_serial_dev_inst *serial,
-		const void *buf, size_t count)
+static int _serial_write(struct sr_serial_dev_inst *serial,
+		const void *buf, size_t count, int nonblocking)
 {
 	ssize_t ret;
 	char *error;
@@ -197,13 +182,15 @@ SR_PRIV int serial_write(struct sr_serial_dev_inst *serial,
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot use unopened serial port %s (fd %d).",
-				serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot use unopened serial port %s.", serial->port);
 		return SR_ERR;
 	}
 
-	ret = sp_write(serial->data, buf, count);
+	if (nonblocking)
+		ret = sp_nonblocking_write(serial->data, buf, count);
+	else
+		ret = sp_blocking_write(serial->data, buf, count, 0);
 
 	switch (ret) {
 	case SP_ERR_ARG:
@@ -211,27 +198,55 @@ SR_PRIV int serial_write(struct sr_serial_dev_inst *serial,
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Write error: %s.", error);
+		sr_err("Write error (%d): %s.", sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
 
-	sr_spew("Wrote %d/%d bytes (fd %d).", ret, count, serial->fd);
+	sr_spew("Wrote %d/%d bytes.", ret, count);
 
 	return ret;
 }
 
 /**
- * Read a number of bytes from the specified serial port.
+ * Write a number of bytes to the specified serial port.
  *
  * @param serial Previously initialized serial port structure.
- * @param buf Buffer where to store the bytes that are read.
- * @param count The number of bytes to read.
+ * @param[in] buf Buffer containing the bytes to write.
+ * @param[in] count Number of bytes to write.
  *
- * @return The number of bytes read, or a negative error code upon failure.
+ * @retval SR_ERR_ARG Invalid argument.
+ * @retval SR_ERR Other error.
+ * @retval other The number of bytes written.
  */
-SR_PRIV int serial_read(struct sr_serial_dev_inst *serial, void *buf,
-		size_t count)
+SR_PRIV int serial_write(struct sr_serial_dev_inst *serial,
+		const void *buf, size_t count)
+{
+	return _serial_write(serial, buf, count, serial->nonblocking);
+}
+
+/**
+ * Write a number of bytes to the specified serial port, blocking until finished.
+ * @copydetails serial_write()
+ */
+SR_PRIV int serial_write_blocking(struct sr_serial_dev_inst *serial,
+		const void *buf, size_t count)
+{
+	return _serial_write(serial, buf, count, 0);
+}
+
+/**
+ * Write a number of bytes to the specified serial port, return immediately.
+ * @copydetails serial_write()
+*/
+SR_PRIV int serial_write_nonblocking(struct sr_serial_dev_inst *serial,
+		const void *buf, size_t count)
+{
+	return _serial_write(serial, buf, count, 1);
+}
+
+static int _serial_read(struct sr_serial_dev_inst *serial, void *buf,
+		size_t count, int nonblocking)
 {
 	ssize_t ret;
 	char *error;
@@ -241,13 +256,15 @@ SR_PRIV int serial_read(struct sr_serial_dev_inst *serial, void *buf,
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot use unopened serial port %s (fd %d).",
-				serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot use unopened serial port %s.", serial->port);
 		return SR_ERR;
 	}
 
-	ret = sp_read(serial->data, buf, count);
+	if (nonblocking)
+		ret = sp_nonblocking_read(serial->data, buf, count);
+	else
+		ret = sp_blocking_read(serial->data, buf, count, 0);
 
 	switch (ret) {
 	case SP_ERR_ARG:
@@ -255,29 +272,70 @@ SR_PRIV int serial_read(struct sr_serial_dev_inst *serial, void *buf,
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Read error: %s.", error);
+		sr_err("Read error (%d): %s.", sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
 
 	if (ret > 0)
-		sr_spew("Read %d/%d bytes (fd %d).", ret, count, serial->fd);
+		sr_spew("Read %d/%d bytes.", ret, count);
 
 	return ret;
 }
 
+/**
+ * Read a number of bytes from the specified serial port.
+ *
+ * @param serial Previously initialized serial port structure.
+ * @param buf Buffer where to store the bytes that are read.
+ * @param[in] count The number of bytes to read.
+ *
+ * @retval SR_ERR_ARG Invalid argument.
+ * @retval SR_ERR     Other error.
+ * @retval other      The number of bytes read.
+ */
+SR_PRIV int serial_read(struct sr_serial_dev_inst *serial, void *buf,
+		size_t count)
+{
+	return _serial_read(serial, buf, count, serial->nonblocking);
+}
+
+/**
+ * Read a number of bytes from the specified serial port, block until finished.
+ * @copydetails serial_read()
+ */
+SR_PRIV int serial_read_blocking(struct sr_serial_dev_inst *serial, void *buf,
+		size_t count)
+{
+	return _serial_read(serial, buf, count, 0);
+}
+
+/**
+ * Try to read up to @a count bytes from the specified serial port, return
+ * immediately with what's available.
+ * @copydetails serial_read()
+ */
+SR_PRIV int serial_read_nonblocking(struct sr_serial_dev_inst *serial, void *buf,
+		size_t count)
+{
+	return _serial_read(serial, buf, count, 1);
+}
+
 /**
  * Set serial parameters for the specified serial port.
  *
  * @param serial Previously initialized serial port structure.
- * @param baudrate The baudrate to set.
- * @param bits The number of data bits to use.
- * @param parity The parity setting to use (0 = none, 1 = even, 2 = odd).
- * @param stopbits The number of stop bits to use (1 or 2).
- * @param flowcontrol The flow control settings to use (0 = none, 1 = RTS/CTS,
- *                    2 = XON/XOFF).
+ * @param[in] baudrate The baudrate to set.
+ * @param[in] bits The number of data bits to use (5, 6, 7 or 8).
+ * @param[in] parity The parity setting to use (0 = none, 1 = even, 2 = odd).
+ * @param[in] stopbits The number of stop bits to use (1 or 2).
+ * @param[in] flowcontrol The flow control settings to use (0 = none,
+ *                      1 = RTS/CTS, 2 = XON/XOFF).
+ * @param[in] rts Status of RTS line (0 or 1; required by some interfaces).
+ * @param[in] dtr Status of DTR line (0 or 1; required by some interfaces).
  *
- * @return SR_OK upon success, SR_ERR upon failure.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_set_params(struct sr_serial_dev_inst *serial, int baudrate,
 			      int bits, int parity, int stopbits,
@@ -292,14 +350,12 @@ SR_PRIV int serial_set_params(struct sr_serial_dev_inst *serial, int baudrate,
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot configure unopened serial port %s (fd %d).",
-		       serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot configure unopened serial port %s.", serial->port);
 		return SR_ERR;
 	}
 
-	sr_spew("Setting serial parameters on port %s (fd %d).", serial->port,
-		serial->fd);
+	sr_spew("Setting serial parameters on port %s.", serial->port);
 
 	sp_new_config(&config);
 	sp_set_config_baudrate(config, baudrate);
@@ -333,7 +389,8 @@ SR_PRIV int serial_set_params(struct sr_serial_dev_inst *serial, int baudrate,
 		return SR_ERR_ARG;
 	case SP_ERR_FAIL:
 		error = sp_last_error_message();
-		sr_err("Error setting serial port parameters: %s.", error);
+		sr_err("Error setting serial port parameters (%d): %s.",
+			sp_last_error_code(), error);
 		sp_free_error_message(error);
 		return SR_ERR;
 	}
@@ -342,19 +399,30 @@ SR_PRIV int serial_set_params(struct sr_serial_dev_inst *serial, int baudrate,
 }
 
 /**
- * Set serial parameters for the specified serial port.
+ * Set serial parameters for the specified serial port from parameter string.
  *
  * @param serial Previously initialized serial port structure.
- * @param paramstr A serial communication parameters string, in the form
- * of <speed>/<data bits><parity><stopbits><flow>, for example "9600/8n1" or
- * "600/7o2" or "460800/8n1/flow=2" where flow is 0 for none, 1 for rts/cts and 2 for xon/xoff.
- *
- * @return SR_OK upon success, SR_ERR upon failure.
+ * @param[in] paramstr A serial communication parameters string of the form
+ * "<baudrate>/<bits><parity><stopbits>{/<option>}".\n
+ *  Examples: "9600/8n1", "600/7o2/dtr=1/rts=0" or "460800/8n1/flow=2".\n
+ * \<baudrate\>=integer Baud rate.\n
+ * \<bits\>=5|6|7|8 Number of data bits.\n
+ * \<parity\>=n|e|o None, even, odd.\n
+ * \<stopbits\>=1|2 One or two stop bits.\n
+ * Options:\n
+ * dtr=0|1 Set DTR off resp. on.\n
+ * flow=0|1|2 Flow control. 0 for none, 1 for RTS/CTS, 2 for XON/XOFF.\n
+ * rts=0|1 Set RTS off resp. on.\n
+ * Please note that values and combinations of these parameters must be
+ * supported by the concrete serial interface hardware and the drivers for it.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
-#define SERIAL_COMM_SPEC "^(\\d+)/([5678])([neo])([12])(.*)$"
 SR_PRIV int serial_set_paramstr(struct sr_serial_dev_inst *serial,
 		const char *paramstr)
 {
+#define SERIAL_COMM_SPEC "^(\\d+)/([5678])([neo])([12])(.*)$"
+
 	GRegex *reg;
 	GMatchInfo *match;
 	int speed, databits, parity, stopbits, flow, rts, dtr, i;
@@ -452,11 +520,12 @@ SR_PRIV int serial_set_paramstr(struct sr_serial_dev_inst *serial,
  * @param serial Previously initialized serial port structure.
  * @param buf Buffer where to store the bytes that are read.
  * @param buflen Size of the buffer.
- * @param timeout_ms How long to wait for a line to come in.
+ * @param[in] timeout_ms How long to wait for a line to come in.
  *
  * Reading stops when CR of LR is found, which is stripped from the buffer.
  *
- * @return SR_OK on success, SR_ERR on failure.
+ * @retval SR_OK Success.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_readline(struct sr_serial_dev_inst *serial, char **buf,
 		int *buflen, gint64 timeout_ms)
@@ -464,14 +533,13 @@ SR_PRIV int serial_readline(struct sr_serial_dev_inst *serial, char **buf,
 	gint64 start;
 	int maxlen, len;
 
-	if (!serial || serial->fd == -1) {
+	if (!serial) {
 		sr_dbg("Invalid serial port.");
 		return SR_ERR;
 	}
 
-	if (serial->fd == -1) {
-		sr_dbg("Cannot use unopened serial port %s (fd %d).",
-				serial->port, serial->fd);
+	if (!serial->data) {
+		sr_dbg("Cannot use unopened serial port %s.", serial->port);
 		return -1;
 	}
 
@@ -512,21 +580,22 @@ SR_PRIV int serial_readline(struct sr_serial_dev_inst *serial, char **buf,
  *
  * @param serial Previously initialized serial port structure.
  * @param buf Buffer containing the bytes to write.
- * @param count Size of the buffer.
- * @param packet_size Size, in bytes, of a valid packet.
+ * @param buflen Size of the buffer.
+ * @param[in] packet_size Size, in bytes, of a valid packet.
  * @param is_valid Callback that assesses whether the packet is valid or not.
- * @param timeout_ms The timeout after which, if no packet is detected, to
+ * @param[in] timeout_ms The timeout after which, if no packet is detected, to
  *                   abort scanning.
- * @param baudrate The baudrate of the serial port. This parameter is not
+ * @param[in] baudrate The baudrate of the serial port. This parameter is not
  *                 critical, but it helps fine tune the serial port polling
  *                 delay.
  *
- * @return SR_OK if a valid packet is found within the given timeout,
- *         SR_ERR upon failure.
+ * @retval SR_OK Valid packet was found within the given timeout.
+ * @retval SR_ERR Failure.
  */
 SR_PRIV int serial_stream_detect(struct sr_serial_dev_inst *serial,
 				 uint8_t *buf, size_t *buflen,
-				 size_t packet_size, packet_valid_t is_valid,
+				 size_t packet_size,
+				 packet_valid_callback is_valid,
 				 uint64_t timeout_ms, int baudrate)
 {
 	uint64_t start, time, byte_delay_us;
@@ -535,8 +604,8 @@ SR_PRIV int serial_stream_detect(struct sr_serial_dev_inst *serial,
 
 	maxlen = *buflen;
 
-	sr_dbg("Detecting packets on FD %d (timeout = %" PRIu64
-	       "ms, baudrate = %d).", serial->fd, timeout_ms, baudrate);
+	sr_dbg("Detecting packets on %s (timeout = %" PRIu64
+	       "ms, baudrate = %d).", serial->port, timeout_ms, baudrate);
 
 	if (maxlen < (packet_size / 2) ) {
 		sr_err("Buffer size must be at least twice the packet size.");
@@ -590,3 +659,253 @@ SR_PRIV int serial_stream_detect(struct sr_serial_dev_inst *serial,
 
 	return SR_ERR;
 }
+
+/**
+ * Extract the serial device and options from the options linked list.
+ *
+ * @param options List of options passed from the command line.
+ * @param serial_device Pointer where to store the exctracted serial device.
+ * @param serial_options Pointer where to store the optional extracted serial
+ * options.
+ *
+ * @return SR_OK if a serial_device is found, SR_ERR if no device is found. The
+ * returned string should not be freed by the caller.
+ */
+SR_PRIV int sr_serial_extract_options(GSList *options, const char **serial_device,
+				      const char **serial_options)
+{
+	GSList *l;
+	struct sr_config *src;
+
+	*serial_device = NULL;
+
+	for (l = options; l; l = l->next) {
+		src = l->data;
+		switch (src->key) {
+		case SR_CONF_CONN:
+			*serial_device = g_variant_get_string(src->data, NULL);
+			sr_dbg("Parsed serial device: %s", *serial_device);
+			break;
+
+		case SR_CONF_SERIALCOMM:
+			*serial_options = g_variant_get_string(src->data, NULL);
+			sr_dbg("Parsed serial options: %s", *serial_options);
+			break;
+		}
+	}
+
+	if (!*serial_device) {
+		sr_dbg("No serial device specified");
+		return SR_ERR;
+	}
+
+	return SR_OK;
+}
+
+#ifdef _WIN32
+typedef HANDLE event_handle;
+#else
+typedef int event_handle;
+#endif
+
+SR_PRIV int serial_source_add(struct sr_session *session,
+		struct sr_serial_dev_inst *serial, int events, int timeout,
+		sr_receive_data_callback cb, void *cb_data)
+{
+	enum sp_event mask = 0;
+	unsigned int i;
+
+	if (sp_new_event_set(&serial->event_set) != SP_OK)
+		return SR_ERR;
+
+	if (events & G_IO_IN)
+		mask |= SP_EVENT_RX_READY;
+	if (events & G_IO_OUT)
+		mask |= SP_EVENT_TX_READY;
+	if (events & G_IO_ERR)
+		mask |= SP_EVENT_ERROR;
+
+	if (sp_add_port_events(serial->event_set, serial->data, mask) != SP_OK) {
+		sp_free_event_set(serial->event_set);
+		return SR_ERR;
+	}
+
+	serial->pollfds = (GPollFD *) g_malloc0(sizeof(GPollFD) * serial->event_set->count);
+
+	for (i = 0; i < serial->event_set->count; i++) {
+
+		serial->pollfds[i].fd = ((event_handle *) serial->event_set->handles)[i];
+
+		mask = serial->event_set->masks[i];
+
+		if (mask & SP_EVENT_RX_READY)
+			serial->pollfds[i].events |= G_IO_IN;
+		if (mask & SP_EVENT_TX_READY)
+			serial->pollfds[i].events |= G_IO_OUT;
+		if (mask & SP_EVENT_ERROR)
+			serial->pollfds[i].events |= G_IO_ERR;
+
+		if (sr_session_source_add_pollfd(session, &serial->pollfds[i],
+					timeout, cb, cb_data) != SR_OK)
+			return SR_ERR;
+	}
+
+	return SR_OK;
+}
+
+SR_PRIV int serial_source_remove(struct sr_session *session,
+		struct sr_serial_dev_inst *serial)
+{
+	unsigned int i;
+
+	for (i = 0; i < serial->event_set->count; i++)
+		if (sr_session_source_remove_pollfd(session, &serial->pollfds[i]) != SR_OK)
+			return SR_ERR;
+
+	g_free(serial->pollfds);
+	sp_free_event_set(serial->event_set);
+
+	serial->pollfds = NULL;
+	serial->event_set = NULL;
+
+	return SR_OK;
+}
+
+/**
+ * Find USB serial devices via the USB vendor ID and product ID.
+ *
+ * @param[in] vendor_id Vendor ID of the USB device.
+ * @param[in] product_id Product ID of the USB device.
+ *
+ * @return A GSList of strings containing the path of the serial device or
+ *         NULL if no serial device is found. The returned list must be freed
+ *         by the caller.
+ */
+SR_PRIV GSList *sr_serial_find_usb(uint16_t vendor_id, uint16_t product_id)
+{
+#ifdef __linux__
+	const gchar *usb_dev;
+	const char device_tree[] = "/sys/bus/usb/devices/";
+	GDir *devices_dir, *device_dir;
+	GSList *l = NULL;
+	GSList *tty_devs;
+	GSList *matched_paths;
+	FILE *fd;
+	char tmp[5];
+	gchar *vendor_path, *product_path, *path_copy;
+	gchar *prefix, *subdir_path, *device_path, *tty_path;
+	unsigned long read_vendor_id, read_product_id;
+	const char *file;
+
+	l = NULL;
+	tty_devs = NULL;
+	matched_paths = NULL;
+
+	if (!(devices_dir = g_dir_open(device_tree, 0, NULL)))
+		return NULL;
+
+	/*
+	 * Find potential candidates using the vendor ID and product ID
+	 * and store them in matched_paths.
+	 */
+	while ((usb_dev = g_dir_read_name(devices_dir))) {
+		vendor_path = g_strconcat(device_tree,
+					  usb_dev, "/idVendor", NULL);
+		product_path = g_strconcat(device_tree,
+					   usb_dev, "/idProduct", NULL);
+
+		if (!g_file_test(vendor_path, G_FILE_TEST_EXISTS) ||
+		    !g_file_test(product_path, G_FILE_TEST_EXISTS))
+			goto skip_device;
+
+		if ((fd = g_fopen(vendor_path, "r")) == NULL)
+			goto skip_device;
+
+		if (fgets(tmp, sizeof(tmp), fd) == NULL) {
+			fclose(fd);
+			goto skip_device;
+		}
+		read_vendor_id = strtoul(tmp, NULL, 16);
+
+		fclose(fd);
+
+		if ((fd = g_fopen(product_path, "r")) == NULL)
+			goto skip_device;
+
+		if (fgets(tmp, sizeof(tmp), fd) == NULL) {
+			fclose(fd);
+			goto skip_device;
+		}
+		read_product_id = strtoul(tmp, NULL, 16);
+
+		fclose(fd);
+
+		if (vendor_id == read_vendor_id &&
+		    product_id == read_product_id) {
+			path_copy = g_strdup(usb_dev);
+			matched_paths = g_slist_prepend(matched_paths,
+							path_copy);
+		}
+
+skip_device:
+		g_free(vendor_path);
+		g_free(product_path);
+	}
+	g_dir_close(devices_dir);
+
+	/* For every matched device try to find a ttyUSBX subfolder. */
+	for (l = matched_paths; l; l = l->next) {
+		subdir_path = NULL;
+
+		device_path = g_strconcat(device_tree, l->data, NULL);
+
+		if (!(device_dir = g_dir_open(device_path, 0, NULL))) {
+			g_free(device_path);
+			continue;
+		}
+
+		prefix = g_strconcat(l->data, ":", NULL);
+
+		while ((file = g_dir_read_name(device_dir))) {
+			if (g_str_has_prefix(file, prefix)) {
+				subdir_path = g_strconcat(device_path,
+						"/", file, NULL);
+				break;
+			}
+		}
+		g_dir_close(device_dir);
+
+		g_free(prefix);
+		g_free(device_path);
+
+		if (subdir_path) {
+			if (!(device_dir = g_dir_open(subdir_path, 0, NULL))) {
+				g_free(subdir_path);
+				continue;
+			}
+			g_free(subdir_path);
+
+			while ((file = g_dir_read_name(device_dir))) {
+				if (g_str_has_prefix(file, "ttyUSB")) {
+					tty_path = g_strconcat("/dev/",
+							       file, NULL);
+					sr_dbg("Found USB device %04x:%04x attached to %s.",
+					       vendor_id, product_id, tty_path);
+					tty_devs = g_slist_prepend(tty_devs,
+							tty_path);
+					break;
+				}
+			}
+			g_dir_close(device_dir);
+		}
+	}
+	g_slist_free_full(matched_paths, g_free);
+
+	return tty_devs;
+#else
+	(void)vendor_id;
+	(void)product_id;
+
+	return NULL;
+#endif
+}