Re: [gpsd-dev] [PATCH] Bump GPS_PATH_MAX to allow using persistent names.

[Marti Bolivar]

On 05/24/2012 05:32 PM, tz wrote:
> Note that this full devicename path is included in the JSON output to
> identify the source.

I'm giving gpsd the path to use as argument, so I have to know it 
beforehand.

> (This was discussed before, and I suggested some ordinal or the file number
> returned by open or something, and I said it would bite - there can also be
> duplicates, e.g. TCP or UDP connections).
>
> There is no speciific reason to have to know or store a system defined file
> path after the device node is opened, but it is being used as part of the
> data.
>
> You are changing it to 128 now, but it might need to be 256 later, e.g. the
> dev path might get vary long if it models the USB device bus tree and
> includes this.  There is no static limit to a full path name, so the real
> alternatives are to malloc it (if you are going to store it and not just
> point to argv or something) or to store something else.

I understand (and respect) the no-malloc policy, and I'm not trying to 
give gpsd a case of C programmer's disease. It's just confusing to first 
see encouraging output like this:

gpsd:INFO: stashing device 
/dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller_D-if00-port0 
at slot 0

Then get strange errors:

gpsd:INFO: opening read-only GPS data source type 0 and at 
'/dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Contr'
gpsd:ERROR: device open failed: No such file or directory - retrying 
read-only
gpsd:ERROR: read-only device open failed: No such file or directory
gpsd:ERROR: 
/dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Contr: device 
activation failed.

I suppose the real fix is to spit out an error immediately if the user 
specifies a path that's longer than GPS_PATH_MAX.

Best,
Marti