Re: [PATCH v2] usbip: tools: Add usbip host driver availability check

[Zongmin Zhou <min_halo@163.com>]

On 2026/3/28 02:29, Shuah Khan wrote:
> On 3/27/26 11:51, Shuah Khan wrote:
>> On 3/27/26 02:39, Zongmin Zhou wrote:
>>>
>>> On 2026/3/27 02:43, Shuah Khan wrote:
>>>> On 3/26/26 02:43, Greg KH wrote:
>>
>> [removed text]
>>
>>>>
>>>> The problem Zongmin is trying fix ish when usbipd starts, it looks for
>>>> exported if any - if it doesn't find any it assumes there aren't any
>>>> exported and doesn't detect that usbip_host driver isn't loaded.
>>>>
>>>> refresh_exported_devices() doesn't have the logic and it shouldn't
>>>> include that logic because this hook is called periodically to
>>>> refresh the list of exported devices. Starting usbipd and loading
>>>> the driver are distinct steps and without any dependencies.
>>>>
>>>> This patch he is trying to add that detection so a message can be 
>>>> printed
>>>> to say "load the driver".
>>>>
>>>> A message can be added easily to cover two cases:
>>>>
>>>> 1. usbip_host driver isn't loaded
>>>> 2. There are no exported devices.
>>>>
>>>> refresh_exported_devices() will not find any devices in both
>>>> of the above scenarios. It isn't an error if it can't find
>>>> any exported devices.
>>>>
>>>> An informational message when refresh_exported_devices()
>>>> when it doesn't find any devices could help users.
>>>>
>>>> Zongmin,
>>>>
>>>> Would adding a message that says
>>>> "Check if usbip_host driver is loaded or export devices"
>>>> solve the problem of hard to debug problem you are addressing here?
>>>>
>>> Shuah,
>>>
>>> Your suggestion makes sense.
>>> Adding an informational message when no devices are found would be a 
>>> simple
>>> and clean solution that helps users debug without being intrusive.
>>>
>>> However, I plan to add the info() message in 
>>> usbip_generic_driver_open() instead of
>>> refresh_exported_devices(), because:
>>> - usbip_generic_driver_open() is called only once at initialization.
>>> - refresh_exported_devices() is called periodically to refresh the 
>>> exported device list.
>>
>> refresh_exported_devices() isn't called periodically - it is called
>> from usbip_host_driver op: refresh_device_list and it will be called
>> whenever usbipd (host side) calls it whenever it receives a request from
>> user-space via process_request()
>>
>> For example running "usbip list -l" command will trigger a run of
>> refresh_exported_devices() via usbip_host_driver op: refresh_device_list
>>
>> I don't think it will that noisy to add a message to 
>> refresh_exported_devices()
>> when device list is zero. Currently the logic doesn't detect device 
>> list zero.
>> You have add that condition to print informational message.
>>
>>
>>> - When the server has no exported devices, having zero devices
>>>    is normal and not worth frequent info messages.
>>
>> That is correct. Zero exported devices isn't an error and this could
>> persist until devices are exported.
>>
>>>
>>> Theoretically, we only need to prompt once at startup. Is my 
>>> understanding correct?> > I'll also remove the existing error 
>>> messages like below,
>>> since they cannot accurately determine whether the driver is loaded:
>>>
>>> if (ret)
>>>      err("please load " USBIP_CORE_MOD_NAME ".ko and "
>>>          USBIP_HOST_DRV_NAME ".ko!");
>>
>> Leave this one alone, because it gets called from a couple of places.
In usbip_generic_driver_open(), the only path that triggers this message 
is a failure of udev_new().
This function fails due to system-level issues like memory exhaustion, 
not because usbip driver module is missing.

Furthermore, since refresh_exported_devices() doesn't practically return 
an error here,
the message is never seen during actual driver loading failures.
So I think it’s better to remove this inaccurate hint to avoid confusing 
the users.

This is the reason why I previously wanted to remove it.
>>
>
> Better yet, why not change the usbip instead - usbip_list for example.
> This is the one that prints the device list and the change can be made
> there when the list is zero to say, "Check if driver is loaded and
> exported devices"
I think placing the check/message in refresh_exported_devices() would be 
more effective.
This function covers all scenarios where the device list is refreshed, 
including:
usbipd startup, usbip list -r, and usbip attach operations.

This way, users receive helpful feedback automatically without needing 
to explicitly run usbip list -r.
>
> thanks,
> -- Shuah