Comment 10 for bug 861642

I would like to use my Linux system to charge up my iOS devices, but I don't want to "Trust this Computer" so maybe we can drill down further on this bug.

As soon as I connect a locked iDevice (tested iOS 9 and iOS 10):

$ top

top - 12:22:28 up 24 days, 21:05, 2 users, load average: 0.50, 0.56, 0.84
Tasks: 222 total, 2 running, 220 sleeping, 0 stopped, 0 zombie
%Cpu(s): 37.7 us, 2.8 sy, 0.0 ni, 59.1 id, 0.5 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 3917996 total, 228612 free, 2176052 used, 1513332 buff/cache
KiB Swap: 4063228 total, 3597580 free, 465648 used. 1188276 avail Mem

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 2184 root 20 0 348112 5596 4800 R 70.4 0.1 3886:07 upowerd

upowerd itself doesn't tell me much:

$ upower --monitor
Monitoring activity from the power daemon. Press Ctrl+C to cancel.
[15:26:55.169] device added: /org/freedesktop/UPower/devices/media_player_1_1

$ upower --monitor-detail
Monitoring activity from the power daemon. Press Ctrl+C to cancel.
[15:28:23.805] device added: /org/freedesktop/UPower/devices/media_player_1_1
  native-path: /sys/devices/pci0000:00/0000:00:14.0/usb1/1-1
  vendor: Apple_Inc.
  model: iPod
  serial: 8b1d0ada9c849c62fd52263c3797034216608bf0
  power supply: no
  updated: Wed 31 Dec 1969 07:00:00 PM EST (1477682903 seconds ago)
  has history: yes
  has statistics: no
  media-player
    warning-level: none
    percentage: 0%
    icon-name: 'battery-missing-symbolic'

perf top: it shows the top four items to be libgmp.so.10.3.0 in:
 __gmpn_redc_1
 __gmpn_sqr_basecase
 __gmpn_mul_basecase
 __gmpz_probab_prime_p

`perf top --sort=comm,dso` shows that the top item is upowerd, in libgmp.so.10.3.0

This is a math library. I can only guess, but it may be doing math operations to compute the UDID of the iOS device every time it tries to communicate with it? Some SHA1 operations maybe.

To use strace on the upowerd process (PID 2184):

$ sudo strace -p 2184 -c
strace: Process 2184 attached
strace: [ Process PID=2184 runs in x32 mode. ]
strace: [ Process PID=2184 runs in 64 bit mode. ]
^Cstrace: Process 2184 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
 58.05 0.000101 1 96 sendto
 41.95 0.000073 0 14494 getrusage
  0.00 0.000000 0 24 close
  0.00 0.000000 0 30 6 stat
  0.00 0.000000 0 6 poll
  0.00 0.000000 0 96 select
  0.00 0.000000 0 24 socket
  0.00 0.000000 0 24 connect
  0.00 0.000000 0 96 recvfrom
------ ----------- ----------- --------- --------- ----------------
100.00 0.000174 14890 6 total

$ sudo strace -p 2184 -e sendto -i
This shows that it is sending XML messages over and over again. For fuller output you can add `-s 999` ... these are XML formatted messages being sent to the iPod as part of some kind of iOS proprietary communications protocol.

You can verify using a USB capture via usbmon, that the host Linux system is in an infinite loop asking the iPod for something. Wireshark doesn't have a dissector for iOS vendor-specific interfaces and commands but you can see the same XML messages traveling the USB bus that were observed in strace.

Is this actually a bug in libimobiledevice ? This seems like a failure to obey an iOS protocol. Supposedly I am already on the latest version: my package is 1.2.0+dfsg-3~ubuntu0.2