chronovu-la: rephrase the USB vendor check during scan

Provide more information in the source code comment on the motivation to
only inspect a given USB VID during scan for ChronoVu LA devices. Use a
different identifier for the expected VID, the previous implementation
was rather misleading.

diff --git a/src/hardware/chronovu-la/api.c b/src/hardware/chronovu-la/api.c
index 5ed496b0bf0c73c14cdc300b102a64d927adc455..d5ca278b728d999557576d291f9720bbfe491b75 100644 (file)
--- a/src/hardware/chronovu-la/api.c
+++ b/src/hardware/chronovu-la/api.c
@@ -20,7 +20,7 @@
 #include <config.h>
 #include "protocol.h"
 
-#define CHRONOVU_VENDOR (0x0403)
+#define SCAN_EXPECTED_VENDOR 0x0403
 
 static const uint32_t scanopts[] = {
        SR_CONF_CONN,
@@ -165,9 +165,20 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
 
                libusb_get_device_descriptor(devlist[i], &des);
 
-               /* See https://sigrok.org/bugzilla/show_bug.cgi?id=1115 and
-                * https://github.com/sigrokproject/libsigrok/pull/166 */
-               if (des.idVendor != CHRONOVU_VENDOR)
+               /*
+                * In theory we'd accept any USB device with a matching
+                * product string. In practice the enumeration takes a
+                * shortcut and only inspects devices when their USB VID
+                * matches the expectation. This avoids access to flaky
+                * devices which are unrelated to measurement purposes
+                * yet cause trouble when accessed including segfaults,
+                * while libusb won't transparently handle their flaws.
+                *
+                * See https://sigrok.org/bugzilla/show_bug.cgi?id=1115
+                * and https://github.com/sigrokproject/libsigrok/pull/166
+                * for a discussion.
+                */
+               if (des.idVendor != SCAN_EXPECTED_VENDOR)
                        continue;
 
                if ((ret = libusb_open(devlist[i], &hdl)) < 0)