serial_posix: be more accepting of device paths

jepler · tormodvolden · commit 75a8bee25a5a · 2015-02-24T21:35:49.000+01:00
On Linux, it is possible to refer to USB serial devices with durable
paths such as /dev/serial/by-path/pci-0000:00:14.0-usb-0:1:1.0-port0 or
/dev/serial/by-id/usb-FTDI_FT232R_USB_UART_A700abCD-if00-port0.  These
paths are themselves symlinks to /dev/tty*.

I have also found it convenient to place symlinks in my build
directories, so that the file 'PORT' names the appropriate device for
the project.

This patch enables both usages, by first using the standard POSIX API
realpath(3) to resolve symbolic links, and only then checks that the
device name starts with /dev/tty.

Signed-off-by: Jeff Epler &lt;jepler@unpythonic.net&gt;
diff --git a/serial_posix.c b/serial_posix.c
@@ -18,6 +18,7 @@
 */
 
 #include <fcntl.h>
+#include <limits.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -197,13 +198,27 @@ static port_err_t serial_setup(serial_t *h, const serial_baud_t baud,
 	return PORT_ERR_OK;
 }
 
+static int startswith(const char *haystack, const char *needle) {
+	return strncmp(haystack, needle, strlen(needle)) == 0;
+}
+
+static int is_tty(const char *path) {
+	char resolved[PATH_MAX];
+
+	if(!realpath(path, resolved)) return 0;
+
+	if(startswith(resolved, "/dev/tty")) return 1;
+
+	return 0;
+}
+
 static port_err_t serial_posix_open(struct port_interface *port,
 				    struct port_options *ops)
 {
 	serial_t *h;
 
 	/* 1. check device name match */
-	if (strncmp(ops->device, "/dev/tty", strlen("/dev/tty")))
+	if (!is_tty(ops->device))
 		return PORT_ERR_NODEV;
 
 	/* 2. check options */
