HAL, FUSE, and serial port GPSs

[Tom Payne]

Hi,

I'm trying to use HAL to automount a fuse filesystem when I plug my
GPS in. It's a bit weird and I don't know if HAL can handle it.

I have a GPS (actually a combined GPS/variometer/altimeter for
paraglider and hang glider pilots) with a USB Serial interface. I've
written a fuse interface to this device that allows you browse and
edit the tracklogs, waypoints, routes, etc. stored on the device,
automatically uploading them to and downloading them from the device
as appropriate. I'd now like to have this userspace filesystem
automount when the device is plugged in. The sequence of events is
fairly convoluted:

1. The device has a built-in USB-to-serial converter so when the
device is initially inserted it appears as a standard Prolific PL-2303
USB-to-serial converter. HAL's Device Manager signals DeviceAdded when
it is inserted.
2. You must communicate with the device over the serial port to
determine whether it is indeed a GPS (rather than, say, anything else
that has a serial interface). This detection can take some time
(several minutes) because the user must press a button on the GPS
before it will respond on the serial port. Assuming it can be
identified as a GPS then you determine the make, model, serial number
and owner's name.
3. Now you have enough information to choose a nice mountpoint (e.g.
including the owner's name) and can call fuse to mount the device.

My current "solution" is to use a daemon that communicates with HAL's
Device Manager via DBUS listening for DeviceAdded signals. When a
serial device is inserted I test it to see if it is a GPS and if it is
I launch fuse. However, this solution feels ugly and I'm sure that
it's possible to achieve the automounting behaviour entirely within
HAL with a carefully crafted FDI file.

I'd be very grateful for an indication as to whether this is possible
in HAL or if I'm trying to do something that should be handled by
something other than HAL. Troublesome aspects are:
- GPS appears as a standard USB-to-serial converter
- the device is a serial device but ends up acting more like a storage device
- the device must be interrogated to detect whether it is a GPS, this
can take several minutes
- the mount command is unusual (e.g. "flytecfs -o device=/dev/ttyUSB0
mountpoint")
- the mountpoint is a function of parameters read from the device
- the unmount command is unusual (i.e. "fusermount -u mountpoint")
- unmount should be called when the device is unplugged

If you're interested, the code itself, written in Python is here:
  http://github.com/twpayne/flytecfs

Many thanks for any help,
-- 
Tom