My MTP Sony Walkman appears in the Dolphin file manager if it is already plugged in when the PC boots.
When I unplug it and plug it back in again, the device says Connecting or Connected, but there is nothing in the file manager.
When I look at the messages, I get:
usb 1-5: USB disconnect, address 7
usb 1-5: new high speed USB device using ehci_hcd and address 8
usb 1-5: New USB device found, idVendor=054c, idProduct=038e
usb 1-5: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-5: Product: WALKMAN
usb 1-5: Manufacturer: Sony
usb 1-5: SerialNumber: 00FF0000000000
usb 1-5: configuration #1 chosen from 1 choice
scsi9 : SCSI emulation for USB Mass Storage devices
usb-storage: device found at 8
usb-storage: waiting for device to settle before scanning
Solution
Edit /usr/share/hal/fdi/preprobe/10osvendor/10-usb-disable-mediacheck.fdi, and include the following entry:
<match key="@storage.physical_device:usb.vendor_id" int="0x054c">/lib/udev/rules.d/60-libmtp8.rules contains a reference to the walkman, I have read that the file is created from the fdi file, but it seems to have a large number of entries in it, when the fdi file is quite empty.
<match key="@storage.physical_device:usb.product_id" int="0x038e">
<merge key="storage.media_detection_enabled" type="bool">false</merge>
</match>
</match>
It is possible to override this configuration file by placing a file of the same name in /etc/udev/rules.d, although this is unlikely to be necessary.
The device is supposedly detected by the udevd daemon.
The hardware abstraction layer daemon insets some rules into the udev configuration so that it is notified of inserted and removed hardware
The hald communicates with applications using dbus (I think).