MTP connection problem with error "libusb_open() failed!"

[Arwen Bu]

Hi all,

As I got the information that chromium os can support MTP connection now,

I tried to test MTP related modules and research them.

Test environment : Release-R38-6158.B  (with some modification for my work)

But after I plugged in my android phone, it could not work.

I tried to find out what happened, so I started "mtpd" services manually.

minijail0 -u mtp -g mtp -G -- /opt/google/mtpd/mtpd -minloglevel=1

And then I plugged in in the phone, it showed,

Device 0 (VID=12d1 and PID=1051) is a Huawei Honor U8860.
libusb_open() failed!: Permission denied
LIBMTP PANIC: Unable to initialize device

I tried to fix this problem, so I found a solution from the network.

I added a file "51-android.rules" in /etc/udev/rules.d, and listed my phone's information in it.

SUBSYSTEM=="usb", ATTR{idVendor}=="12d1", ATTR{idProduct}=="1051", MODE="0666"

Then I restarted udev service and mtpd service, tried to connect my phone again, it worked.

Device 0 (VID=12d1 and PID=1051) is a Huawei Honor U8860.

Android device detected, assigning default bug flags

But, I tried my phone in my chromebook, it worked well without "51-android.rules".

And I searched in libmtp support list, device 12d1:1051 was already supported.

I tried another Sansung phone, it showed the same problem.

Device 0 (VID=04e8 and PID=6860) is a Samsung Galaxy models (MTP).

libusb_open() failed!: Permission denied

LIBMTP PANIC: Unable to initialize device

I don't think it's a good idea to change "51-android.rules" each time I plug in a different device.

So it should work as chromebook which can access different devices automatically.

I think maybe some configuration I modified causes this problem, but I cannot find out what it is.

Would you please help to provide some suggestion what problem may cause this error?

Thanks.

A.B

[Mike Frysinger]

[ +thestig ]

-mike

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[Lei Zhang]

(Replying again for chromium-os-dev to see)

Hi Arwen,

Are you saying Chromebooks can access MTP devices without any
problems, but your custom ChromiumOS environment requires an
additional udev rule to make it work?

[Arwen Bu]

Hi Lei,

Yes. 

I guess some problem with udev, but I cannot confirm it.

[Lei Zhang]

The only extra rule I remember adding is in 55-mtpd.rules in [1]. I
don't recall touching udev beyond that. I can go look at one of the
Chromebooks in the office that's in dev mode and see what the udev
rules are there. You can too in dev mode. [2]

[1] https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/master/chromeos-base/chromeos-base/files/udev-rules/
[2] http://www.chromium.org/chromium-os/poking-around-your-chrome-os-device

[Arwen Bu]

Hi Lei,

I tried this, but it doesn't take effort.

[Lei Zhang]

I tested with a Chromebook: the /dev/bus/usb/MMM/NNN device node is
owned by root:usb with permission 664. The mtp user that runs mtpd is
also in the usb group according to /etc/group.