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

Zongmin Zhou
2026-04-01T02:47:24Z

On 2026/4/1 08:27, Shuah Khan wrote:
> On 3/31/26 03:58, Zongmin Zhou wrote:
>> From: Zongmin Zhou <zhouzongmin@kylinos.cn>
>>
>> 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@linuxfoundation.org>
>> Signed-off-by: Zongmin Zhou <zhouzongmin@kylinos.cn>
>> ---
>> 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);
>
> Check coding guidelines and match the new code to the existing. Need a
> space between
> the string and the next argument.
>
>
>> +        else
>> +            info("Please check if %s driver is loaded or export
>> devices.",USBIP_DEVICE_DRV_NAME);
>
> When will this be true? Isn't refresh_exported_devices() called from
>
> Thinking about this more, since you have to differentiate between
> host and device, it makes sense to make this change to
>
> usbip_device_driver_open() and usbip_host_driver_open()
> There is an err() message already in both of these routines.
> that prints the right information.
>
Shuah,

Regarding your comment about the existing err() message in these routines:

The existing err("please load *.ko") message only triggers when
usbip_generic_driver_open()
returns a non-zero value. Since refresh_exported_devices() always returns 0
(even when ndevs == 0 and no devices are found), usbip_generic_driver_open()
only returns non-zero when udev_new() fails.

Therefore, when ndevs == 0, the existing err() message is never printed,
so it doesn't actually help users diagnose the "no devices found or
driver not load" situation.

This is exactly why I previously suggested removing this misleading
err() message.

Best regards,
Zongmin
> You can check hdriver->ndevs == 0 and add an info that says
> load appropriate modules or export devices. This way you
> don't have to add logic to refresh_exported_devices() to figure
> out which driver.
>
> thanks,
> -- Shuah