dcttech-usbrelay: accept conn=sn=<serno> user specs in probe

Add support for the "-d dcttech-usbrelay:conn=sn=<serno>" syntax.

This dramatically increases usability when multiple cards are attached
(a very likely condition given the low channel count of these devices),
while other means to select one card out of a set of cards either don't
exist or are heavily constrained: Identical VID:PID numbers are shared
across all card variants. HIDAPI paths are rather platform dependent and
may even be incompatible with the conn= syntax. Some platforms may even
refuse to open() paths which result from their own enumeration. Which
leaves relay card serial numbers as the only reliable and portable
method for selection. Being convenient is just a bonus.

diff --git a/src/hardware/dcttech-usbrelay/api.c b/src/hardware/dcttech-usbrelay/api.c
index a24025ec84376878d17c778bb4808f4fd622547a..137277d0176b014758883bba82d988cd1c58a985 100644 (file)
--- a/src/hardware/dcttech-usbrelay/api.c
+++ b/src/hardware/dcttech-usbrelay/api.c
@@ -45,7 +45,7 @@ static const uint32_t devopts_cg[] = {
 static struct sr_dev_driver dcttech_usbrelay_driver_info;
 
 static struct sr_dev_inst *probe_device_common(const char *path,
-       uint16_t vid, uint16_t pid,
+       uint16_t vid, uint16_t pid, const char *want_serno,
        const wchar_t *vendor, const wchar_t *product)
 {
        char nonws[16], *s, *endp;
@@ -128,6 +128,12 @@ static struct sr_dev_inst *probe_device_common(const char *path,
        sr_info("HID report data: serial number %s, relay state 0x%02x.",
                serno, curr_state);
 
+       /* Optionally filter by serial number. */
+       if (want_serno && *want_serno && strcmp(serno, want_serno) != 0) {
+               sr_dbg("Serial number does not match user spec. Skipping.");
+               return NULL;
+       }
+
        /* Create a device instance. */
        sdi = g_malloc0(sizeof(*sdi));
        sdi->vendor = g_strdup_printf("%ls", vendor);
@@ -158,9 +164,10 @@ static struct sr_dev_inst *probe_device_common(const char *path,
        return sdi;
 }
 
-static struct sr_dev_inst *probe_device_enum(struct hid_device_info *dev)
+static struct sr_dev_inst *probe_device_enum(struct hid_device_info *dev,
+       const char *want_serno)
 {
-       return probe_device_common(dev->path, 0, 0,
+       return probe_device_common(dev->path, 0, 0, want_serno,
                dev->manufacturer_string, dev->product_string);
 }
 
@@ -231,7 +238,7 @@ static struct sr_dev_inst *probe_device_conn(const char *path)
        if (!ok)
                return NULL;
 
-       return probe_device_common(path, vid, pid, vendor, product);
+       return probe_device_common(path, vid, pid, NULL, vendor, product);
 }
 
 static GSList *scan(struct sr_dev_driver *di, GSList *options)
@@ -239,6 +246,7 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
        const char *conn;
        GSList *devices;
        struct drv_context *drvc;
+       char want_serno[SERNO_LENGTH + 1];
        struct hid_device_info *devs, *curdev;
        wchar_t *ws;
        char nonws[32];
@@ -257,14 +265,25 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
        /*
         * The firmware is V-USB based. The USB VID:PID identification
         * is shared across several projects. Need to inspect the vendor
-        * and product _strings_ to actually identify the device. The
-        * USB serial number need not be present nor reliable. The HID
-        * report content will carry the board's serial number.
+        * and product _strings_ to actually identify the device.
+        *
+        * The USB serial number need not be present nor reliable. The
+        * HID report content will carry the board's serial number.
+        * When users specify "sn=..." connection strings, then run a
+        * regular USB enumation, and filter the result set by serial
+        * numbers which only become available with HID reports.
         *
-        * When conn= was specified, then have HIDAPI open _this_ device
-        * and skip the enumeration. Which allows users to specify paths
-        * that need not match the enumeration's details.
+        * When other connection strings were specified, then have
+        * HIDAPI open _this_ device and skip the enumeration. Which
+        * allows users to specify paths that need not match the
+        * enumeration's details.
         */
+       memset(want_serno, 0, sizeof(want_serno));
+       if (conn && g_str_has_prefix(conn, "sn=")) {
+               conn += strlen("sn=");
+               snprintf(want_serno, sizeof(want_serno), "%s", conn);
+               conn = NULL;
+       }
        if (conn) {
                sr_info("Checking HID path %s.", conn);
                sdi = probe_device_conn(conn);
@@ -303,11 +322,9 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
 
                /* Identify device by communicating to it. */
                sr_info("Checking HID path %s.", curdev->path);
-               sdi = probe_device_enum(curdev);
-               if (!sdi) {
-                       sr_warn("Failed to communicate to %s.", curdev->path);
+               sdi = probe_device_enum(curdev, want_serno);
+               if (!sdi)
                        continue;
-               }
                devices = g_slist_append(devices, sdi);
        }
        hid_free_enumeration(devs);