How to tell if a usb mass storage device is plugged in using dbus

Question

If you could go with UDisks2 DBus interface the answer would be quite simple :-) First of all, it seems that UDisks2 (and probably UDisks1, but I haven't it installed) handles only Mass Storage devices connected via USB, completely ignoring USB-connected MTP-devices and other kinds of USB devices such as printers and mice. Have a look:

Right now I have 6 USB devices connected:

alex@galene ~ $ /usr/sbin/lsusb | grep -v 'root hub'
Bus 001 Device 004: ID 058f:6362 Alcor Micro Corp. Flash Card Reader/Writer
Bus 001 Device 003: ID 09da:000a A4 Tech Co., Ltd Optical Mouse Opto 510D
Bus 008 Device 090: ID 04e8:6860 Samsung Electronics Co., Ltd GT-I9100 Phone [Galaxy S II], GT-P7500 [Galaxy Tab 10.1]
Bus 008 Device 075: ID 04b8:0007 Seiko Epson Corp. Printer
Bus 009 Device 002: ID 058f:6387 Alcor Micro Corp. Flash Drive
Bus 009 Device 088: ID 1058:1010 Western Digital Technologies, Inc. Elements External HDD

058f:6362 is an "all-in one" card reader w/ a SD-card currently plugged in. 058f:6387 and 1058:1010 are real USB Mass Storage devs, a flash and an external HDD respectively. 04e8:6860 is a Samsung Galaxy Note1 (an MTP-device) and the rest are the mouse and the printer.

Also I have an internal SATA drive.

Here's the current udisksctl status output (as you may see Galaxy Note is missing):

MODEL                     REVISION  SERIAL               DEVICE
--------------------------------------------------------------------------
Hitachi HDT725040VLA360   V5COA7EA  VFM301R3196R5F       sda     
Generic Flash Disk        8.07      8D0147DF             sdb     
WDC WD1200BEVS-22RST0     04.01G04  WD-WXE108V72690      sdc     
Generic USB CF Reader     1.01      058F312D81B          sde     
Generic USB SM Reader     1.02      058F312D81B          sdf     
Generic USB MS Reader     1.03      058F312D81B          sdg     
Generic USB SD Reader     1.00      058F312D81B          sdd

To distinguish pluggable USB Mass storage devices from stationary drives one may check 'ConnectedBus' and ''Removable' properties. Please note that there's another property 'MediaRemovable' which corresponds to the physical media of the device. Here's the script which selects removable USB Mass Storage devices and prints their 'MediaRemovable' property

alex@galene ~ $ cat <<EOF | python -
> import dbus
> bus = dbus.SystemBus()
> ud_manager_obj = bus.get_object('org.freedesktop.UDisks2', '/org/freedesktop/UDisks2')
> om = dbus.Interface(ud_manager_obj, 'org.freedesktop.DBus.ObjectManager')
> for k,v in om.GetManagedObjects().iteritems():
>     drive_info = v.get('org.freedesktop.UDisks2.Drive', {})
>     if drive_info.get('ConnectionBus') == 'usb' and drive_info.get('Removable'):
>         print("Device Path: %s, MediaRemovable: %s" % (k, drive_info['MediaRemovable']))
> block_devices =  [''.join(chr(c) for c in device[dbus.String(u'org.freedesktop.UDisks2.Block')][dbus.String(u'PreferredDev‌ice')] if chr(c) != '\x00' ) for device in om.GetManagerObjects().values() if dbus.String(u'org.freedesktop.UDisks2.Block') in device]
> EOF
Device Path: /org/freedesktop/UDisks2/drives/Generic_USB_SM_Reader_058F312D81B, MediaRemovable: 1
Device Path: /org/freedesktop/UDisks2/drives/Generic_Flash_Disk_8D0147DF, MediaRemovable: 1
Device Path: /org/freedesktop/UDisks2/drives/Generic_USB_SD_Reader_058F312D81B, MediaRemovable: 1
Device Path: /org/freedesktop/UDisks2/drives/WDC_WD1200BEVS_22RST0_WD_WXE108V72690, MediaRemovable: 0
Device Path: /org/freedesktop/UDisks2/drives/Generic_USB_CF_Reader_058F312D81B, MediaRemovable: 1
Device Path: /org/freedesktop/UDisks2/drives/Generic_USB_MS_Reader_058F312D81B, MediaRemovable: 1

Basically it solves the problem you're trying to solve. Rumors say that there're non-removable USB-connected storage devices but I haven't seen such.