Re: [gpsd-dev] Another release seems called for

[Fulup Le Foll]

Gary

Naming of device is not a question of timeout but a question of availability of the path. Typically this is what's happen and why behaviour may seems to depend on timeout.

• gpsd is running is keep open /dev/ttyUSB0
• you unplug the device
• gpsd fail and retry opening /dev/ttyUSB0  (some other program like opencpn keeps it open for ever)
  
• you plug USB device again
• shift of luck gpsd is still retrying to open /dev/ttyUSB0. As path is busy udev take the next available one
• you're lucky gpsd stop trying to reopen and /dev/ttyUSB0 is available.

It is very easy to trace with tree windows running following commands.

1. gpsd in debug mode
2. udev in debug mode
   
3. lsof /dev/ttyUSB0 running in loop

The only system I found to bypass this issue is to provide fix alias name with a udev script. Creating a device with a name base on its USB slot with "SYMLINK="gps-$env{ID_PATH}" work pretty well on any distribution. This method works even if you have multiple USB/serial adaptors with the same vendor/product id.

One possible alternative could be for gpsd to check if /dev/ttyUSB0 exist before trying to open it. I never check this, but file existence API may only impact directory and thus not lock the path.

Fulup

Le 24/07/2013 19:32, Gary E. Miller a écrit :

Yo Fulup!

On Wed, 24 Jul 2013 10:22:47 +0200
Fulup Le Foll <address@hidden> wrote:

If you plug/unplug an active USB device on Linux. Usually the device 
change name and move for example from ttyUSB0 to ttyUSB1.

Depends on how long.  For me if I wait more than about 30 seconds I'll
get ttyUSB0 again.  I depend on that behavior.

I commented this Linux feature long time ago on 
http://lists.berlios.de/pipermail/gpsd-users/2009-June/003785.html

Might also be useful to highlight that by default last versions of 
Ubuntu does not grant "dialout" group to basic users, when acces to 
/dev/tty* require access to "dialout" group.

Ouch.  So ubuntu is 'dialout' and not the conventional 'uucp' group?

I'd like to add a configure option to allow forcing the group 
gpsd uses after dropping priviledges, then I could completely sidestep 
udev which is non-portable.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
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Fulup


Le 23/07/2013 19:42, Jeroen Massar a écrit :

On 2013-07-23 19:37 , Gary E. Miller wrote:

Yo Eric!

On Tue, 23 Jul 2013 08:24:01 -0400 (EDT)
address@hidden  (Eric S. Raymond) wrote:

I'd like to ship a bugfix release next week.

Maybe another bug to look at before a release:

If I unplug a USB GPS, then plug it back in, then gpsd can no
longer access the device:

gpsd:INFO: reconnection attempt on device 0
gpsd:INFO: opening GPS data source type 3 at '/dev/ttyUSB0'
gpsd:ERROR: device open failed: Permission denied - retrying
read-only gpsd:ERROR: read-only device open failed: Permission
denied gpsd:ERROR: /dev/ttyUSB0: device activation failed.

I assume because priviledges dropped.

Depending on platform, if on Linux you can teach udev to set the
permissions so that gpsd can access it.

Greets,
  Jeroen

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