[Nut-upsuser] usbhid-ups dying, consistently

[Nicholas Leippe]

On Thu, Dec 31, 2015 at 4:43 PM, Charles Lepple <clepple at gmail.com> wrote:

> Thanks for the libusb version numbers. By the way, which version of NUT
> are you using?
>
>
nut-2.7.3


> On Dec 31, 2015, at 6:23 PM, Nicholas Leippe <leippe at gmail.com> wrote:
> >
> > I haven't cracked open the nut sources yet, but am curious why it should
> fail to open the usb device after already succeeding many times.
> > Could it be a USB power management issue? Or simply opening it too many
> times somehow breaks it?
>
> One major difference between the initial startup of usbhid-ups and when it
> tries to reconnect: in the former case, the USB stack has had time to fully
> start up all of the kernel-side drivers.
>
> When usbhid-ups attempts to claim the UPS HID interface for the first time
> after the UPS is plugged in (or has reattached itself), the kernel USB HID
> driver causes an EBUSY return code ("failed to claim USB device: Device or
> resource busy"). Usually, the EBUSY code goes away after usbhid-ups tells
> the kernel to relinquish the interface (line 271 [*]), but in your case, it
> is possible that the USB HID driver hasn't completely started up. This
> might explain the "failed to detach kernel driver from USB device: No such
> file or directory" error.
>
> [*]
> https://github.com/networkupstools/nut/blob/master/drivers/libusb.c#L271
>
> Since dmesg now shows timestamps, you might want to check to see the time
> delta between when the UPS is first detected, and when USB-related messages
> stop appearing. It's about half a second on this Raspberry Pi (which
> incidentally is now running a 4.1.x kernel):
>
> [    2.893909] usb 1-1.2: new low-speed USB device number 4 using dwc_otg
> [    3.041108] usb 1-1.2: New USB device found, idVendor=09ae,
> idProduct=3016
> [    3.050101] usb 1-1.2: New USB device strings: Mfr=3, Product=1,
> SerialNumber=5
> [    3.059367] usb 1-1.2: Product: TRIPP LITE UPS
> [    3.065704] usb 1-1.2: Manufacturer: Tripp Lite
> [    3.558046] hid-generic 0003:09AE:3016.0001: hiddev0,hidraw0: USB HID
> v1.11 Device [Tripp Lite TRIPP LITE UPS] on usb-20980000.usb-1.2/input0
>
> Note that NUT does not use the kernel USB HID drivers, which is why it has
> to detach those drivers to allow libusb to connect.
>
> Other than the reconnection attempts, usbhid-ups only fully opens the UPS
> USB device once.
>

This is then what confuses me, because it *works* and then dies. If it
opens it only once, then why would it fail opening it again--wouldn't it
just hold it open and continue to work? It's never failing to start, it's
failing to continue working.
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