Re: [Xen-devel] [PATCH V15 4/6] libxl: add pvusb API

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Mar 3, 2016 at 2:59 AM, Chun Yan Liu <cyliu@xxxxxxxx> wrote:
>>>> On 3/3/2016 at 02:46 AM, in message <56D7350F.7010000@xxxxxxxxxx>, George
> Dunlap <george.dunlap@xxxxxxxxxx> wrote:
>> Sorry, just looked through the rest of the series, and there's one more
>> thing.
>>
>> Neither here nor in the man page do we explain what to do if something
>> goes wrong with the detach.  I think the best thing to do is probably to
>> make the logged error messages more helpful.
>>
>> What about something like this:
>>
>> * On failure to unbind: "Error removing device from guest.  Try running
>> usbdev-detach again."
>>
>> * On failure to rebind: "USB device removed from guest, but couldn't
>> re-bind to domain 0.  Try removing and re-inserting the USB device or
>> reloading the driver modules."
> Here, user could first try 'echo xxx > sysfs_driver_path/bind", so maybe:
> "Try binding USB device to original driver by echoing the device to
> [driver_path]/bind, or removing and re-inserting the USB device, or
> reloading the driver modules."

Yes, I had thought about the idea of giving the user specific commands
to retry.  The question is how much we can expect the user to do to
recover the state.  At some point "reloading the driver module" was
seen as something reasonable for a reasonably advanced user, while
"messing around with sysfs" was seen to be something too technical.
But as you say, giving them the exact command to cut-and-paste might
be somewhat more reasonable.

I'm still inclined to say that we should just stick with module
reloading and removing and re-inserting the device, but I wouldn't
insist on it.

If we do print this kind of help message, then we should make sure to
print a more complete message that includes cut-and-paste commands for
*all* remaining unbound interfaces.

 -George

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