Nut upsdev - Mar 2010 - usbhid-ups fails with Belkin F6C120-UNV in nut-2.4.3

I recently upgraded from nut-2.4.1 to 2.4.3 and my UPS stopped working.
usbhid-ups now fails two communicate with the UPS:

With 2.4.1:
# /sbin/usbhid-ups -D -a auto
Network UPS Tools - Generic HID driver 0.34 (2.4.1)
USB communication driver 0.31
debug level is '1'
upsdrv_initups...
Using subdriver: Belkin HID 0.12
Path: UPS.BELKINConfig.BELKINConfigVoltage, Type: Feature, ReportID: 0x01,
Offset: 0, Size: 8, Value: 230.000000
Path: UPS.BELKINConfig.BELKINConfigFrequency, Type: Feature, ReportID: 0x02,
Offset: 0, Size: 8, Value: 50.000000
Path: UPS.BELKINConfig.BELKINConfigApparentPower, Type: Feature, ReportID: 0x03,
Offset: 0, Size: 16, Value: 1200.000000
Path: UPS.BELKINConfig.BELKINConfigBatteryVoltage, Type: Feature, ReportID:
0x04, Offset: 0, Size: 16, Value: 24.000000
Path: UPS.BELKINConfig.BELKINConfigOverloadTransfer, Type: Feature, ReportID:
0x05, Offset: 0, Size: 8, Value: 100.000000
...

With 2.4.3:
# /sbin/usbhid-ups -D -a auto
Network UPS Tools - Generic HID driver 0.34 (2.4.3)
USB communication driver 0.31
   0.000000     debug level is '1'
   0.001172     upsdrv_initups...
   0.279899     Using subdriver: Belkin HID 0.12
   0.284577     libusb_get_report: No error
   0.284609     Can't retrieve Report 01: Operation not permitted
   0.284628     Path: UPS.BELKINConfig.BELKINConfigVoltage, Type: Feature,
ReportID: 0x01, Offset: 0, Size: 8
   0.289575     libusb_get_report: No error
   0.289590     Can't retrieve Report 02: Operation not permitted
   0.289602     Path: UPS.BELKINConfig.BELKINConfigFrequency, Type: Feature,
ReportID: 0x02, Offset: 0, Size: 8
   0.294574     libusb_get_report: No error
   0.294589     Can't retrieve Report 03: Operation not permitted
   0.294601     Path: UPS.BELKINConfig.BELKINConfigApparentPower, Type: Feature,
ReportID: 0x03, Offset: 0, Size: 16
   0.299576     libusb_get_report: No error
..


The change in SVN r2098 triggers the problem. By looking at the usbmon
output I see that this device fails to respond to the get_report
requests when the request size is 512 bytes. The requests worked
correctly when they were using the sizes reported by the device:

usbmon get_report() requests from nut-2.4.1
The length of each request matches the response from the device and
works:

ffff880102d5ec00 1618372802 S Ci:7:002:0 s a1 01 0301 0000 0002 2 <
ffff880102d5ec00 1618376440 C Ci:7:002:0 0 2 = 01e6
ffff880102d5ec00 1618376497 S Ci:7:002:0 s a1 01 0302 0000 0002 2 <
ffff880102d5ec00 1618381439 C Ci:7:002:0 0 2 = 0232
ffff880102d5ec00 1618381469 S Ci:7:002:0 s a1 01 0303 0000 0003 3 <
ffff880102d5ec00 1618385439 C Ci:7:002:0 0 3 = 03b004
ffff880102d5ec00 1618385469 S Ci:7:002:0 s a1 01 0304 0000 0003 3 <
ffff880102d5ec00 1618389440 C Ci:7:002:0 0 3 = 041800

usbmon get_report() requests from nut-2.4.3
Now the code always requests 512 bytes and never gets back any data:

ffff88002b799d80 593626443 S Ci:7:002:0 s a1 01 0301 0000 0200 512 <
ffff88002b799d80 593631086 C Ci:7:002:0 0 0
ffff88002b799d80 593631161 S Ci:7:002:0 s a1 01 0302 0000 0200 512 <
ffff88002b799d80 593636087 C Ci:7:002:0 0 0
ffff88002b799d80 593636142 S Ci:7:002:0 s a1 01 0303 0000 0200 512 <
ffff88002b799d80 593641085 C Ci:7:002:0 0 0
ffff88002b799d80 593641136 S Ci:7:002:0 s a1 01 0304 0000 0200 512 <
ffff88002b799d80 593646085 C Ci:7:002:0 0 0

I can workaround this by using the attached patch. Each of the failed
512 byte reads triggers a superfluous log message as below but at least
it works. 

$ sudo ./drivers/usbhid-ups -D -a auto
Network UPS Tools - Generic HID driver 0.34 (2.4.3)
USB communication driver 0.31
   0.000000     debug level is '1'
   0.000652     upsdrv_initups...
   0.277074     Using subdriver: Belkin HID 0.12
   0.281742     libusb_get_report: No error
   0.285758     Path: UPS.BELKINConfig.BELKINConfigVoltage, Type: Feature,
ReportID: 0x01, Offset: 0, Size: 8, Value: 230.000000
   0.290742     libusb_get_report: No error
   0.294749     Path: UPS.BELKINConfig.BELKINConfigFrequency, Type: Feature,
ReportID: 0x02, Offset: 0, Size: 8, Value: 50.000000
   0.299745     libusb_get_report: No error
   0.303753     Path: UPS.BELKINConfig.BELKINConfigApparentPower, Type: Feature,
ReportID: 0x03, Offset: 0, Size: 16, Value: 1200.000000
   0.308744     libusb_get_report: No error
   0.312755     Path: UPS.BELKINConfig.BELKINConfigBatteryVoltage, Type:
Feature, ReportID: 0x04, Offset: 0, Size: 16, Value: 24.000000

	Jon

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Citeren Jon Burgess <jburgess777 op googlemail.com>:

> The change in SVN r2098 triggers the problem. By looking at the usbmon
> output I see that this device fails to respond to the get_report
> requests when the request size is 512 bytes.
Thanks for reporting this. Can you try if fixing the size to 8 bytes  
(instead of SMALLBUF) helps? You may wish to change both of the  
following lines in in 'drivers/libhid.c':

144 	        unsigned char   buf[8];
472 	        unsigned char   buf[8];

I vaguely remember that you can't read more than 8 bytes in a single  
operation, but I don't recall if this is a Belkin specific limitation  
or depends on the libusb version used.

Note that the logic that attempted to calculate the size of reports is  
flawed in earlier versions. Devices that would report more than the  
calculated size would find that these reports would be ignored  
completely. This isn't good either.

Best regards, Arjen
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