scan context: allow mutltiple backends for scanning context

In the past iio_create_scan_context() would take a null terminated
string, like "local" or "ip", and would filter only on that backend.

In addition do that, allow multiple, like "local:ip:usb:", or "ip:usb:"

Signed-off-by: Robin Getz <[email protected]>

iio.h

@@ -205,8 +205,10 @@ enum iio_modifier {
 
 
 /** @brief Create a scan context
- * @param backend A NULL-terminated string containing the backend to use for
- * scanning. If NULL, all the available backends are used.
+ * @param backend A NULL-terminated string containing the backend(s) to use for
+ * scanning (example: pre version 0.20 :  "local", "ip", or "usb"; post version
+ * 0.20 can handle multiple, including "local:usb:", "ip:usb:", "local:usb:ip:").
+ * If NULL, all the available backends are used.
  * @param flags Unused for now. Set to 0.
  * @return on success, a pointer to a iio_scan_context structure
  * @return On failure, NULL is returned and errno is set appropriately */

scan.c

@@ -153,15 +153,15 @@ struct iio_scan_context * iio_create_scan_context(
 		return NULL;
 	}
 
-	if (!backend || !strcmp(backend, "local"))
+	if (!backend || strstr(backend, "local"))
 		ctx->scan_local = true;
 
 #ifdef WITH_USB_BACKEND
-	if (!backend || !strcmp(backend, "usb"))
+	if (!backend || strstr(backend, "usb"))
 		ctx->usb_ctx = usb_context_scan_init();
 #endif
 #ifdef HAVE_DNS_SD
-	if (!backend || !strcmp(backend, "ip"))
+	if (!backend || strstr(backend, "ip"))
 		ctx->dnssd_ctx = dnssd_context_scan_init();
 #endif