Chrome OS Version: 8120.0.0
Chrome OS Platform: any

Steps To Reproduce:
(1) plug gnubby into USB
(2) inspect /var/log/messages
(3)

Expected Result:

No debug spew from mtpd

Actual Result:

2016-03-28T18:20:25.353331+08:00 ERR mtpd[2423]: LIBMTP_Detect_Raw_Devices failed with 5


How frequently does this problem reproduce? (Always, sometimes, hard to
reproduce?)

Always.

What is the impact to the user, and is there a workaround? If so, what is
it?

Excessive log spam increases cognitive load.

Please provide any additional information below. Attach a screen shot or
log if possible.

A brief peek at mtpd [0] and libmtp [1] shows that LIBMTP_Detect_Raw_Devices() can propagate LIBMTP_ERROR_NO_DEVICE_ATTACHED from get_mtp_usb_device_list() (if there is no MTP device attached?):

[0] https://chromium.googlesource.com/chromiumos/platform/mtpd/+/master/device_manager.cc
[1] http://libmtp.sourcearchive.com/documentation/0.3.4/group__basic_ge54131d2a1ed21292fa270921afb9d46.html

It is probably not necessary to spam the log in this case during DeviceManager::AddOrUpdateDevices() [0]:
[2] https://chromium.googlesource.com/chromiumos/platform/mtpd/+/master/device_manager.cc#649

0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 652)   LIBMTP_error_number_t err =
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 653)       LIBMTP_Detect_Raw_Devices(&raw_devices, &raw_devices_count);
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 654)   if (err != LIBMTP_ERROR_NONE) {
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 655)     LOG(ERROR) << "LIBMTP_Detect_Raw_Devices failed with " << err;
5e6caea5 (Kevin Bailey   2013-11-14 07:04:57 -0800 656)     return NULL;
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 657)   }


A similar check already exists in DeviceManager::RemoveDevices() [3]:
[3] https://chromium.googlesource.com/chromiumos/platform/mtpd/+/master/device_manager.cc#649

0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 773)   if (!remove_all) {
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 774)     LIBMTP_error_number_t err =
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 775)         LIBMTP_Detect_Raw_Devices(&raw_devices, &raw_devices_count);
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 776)     if (!(err == LIBMTP_ERROR_NONE || err == LIBMTP_ERROR_NO_DEVICE_ATTACHED)) {
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 777)       LOG(ERROR) << "LIBMTP_Detect_Raw_Devices failed with " << err;
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 778)       return;
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 779)     }
0e5015f2 (Lei Zhang      2012-08-06 17:05:33 -0700 780)   }