[PATCH v3] usbip: tools: add hint when no exported devices are found

[Zongmin Zhou]

From: Zongmin Zhou <zhouzongmin@xxxxxxxxxx>

When refresh_exported_devices() finds no devices, it's helpful to
inform users about potential causes. This could be due to:

1. The usbip driver module is not loaded.
2. No devices have been exported yet.

Add an informational message to guide users when ndevs == 0.

Message visibility by scenario:
- usbipd (console mode): Show on console/serial, this allows instant
  visibility for debugging.
- usbipd -D (daemon mode): Message logged to syslog, can keep logs for
  later traceability in production. Also can use "journalctl -f" to
  trace on console.

Suggested-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Zongmin Zhou <zhouzongmin@xxxxxxxxxx>
---
Changes in v3:
- Just add an informational message when no devices are found.
Changes in v2:
- Use system calls directly instead of checking sysfs dir.

 tools/usb/usbip/libsrc/usbip_host_common.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/usb/usbip/libsrc/usbip_host_common.c b/tools/usb/usbip/libsrc/usbip_host_common.c
index ca78aa368476..cd92baee310c 100644
--- a/tools/usb/usbip/libsrc/usbip_host_common.c
+++ b/tools/usb/usbip/libsrc/usbip_host_common.c
@@ -149,6 +149,13 @@ static int refresh_exported_devices(struct usbip_host_driver *hdriver)
 		}
 	}
 
+	if (hdriver->ndevs == 0) {
+		if (!strcmp(hdriver->udev_subsystem, "usb"))
+			info("Please check if %s driver is loaded or export devices.",USBIP_HOST_DRV_NAME);
+		else
+			info("Please check if %s driver is loaded or export devices.",USBIP_DEVICE_DRV_NAME);
+	}
+
 	return 0;
 }
 
-- 
2.34.1