Re: [PATCH] udevng: Add OFONO_PATHNAME property to set modem dbus path name

[Denis Kenzior <denkenz@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2171 bytes --]

Hi Pau,

On 02/13/2018 01:53 PM, Pau Espin Pedrol wrote:
> The current udevng.c implementation sets dbus path names for modems
> based on type and a number incremented seuqntially for each new modem
> found. As a result, the dbus path for a given device is non
> deterministic, since it depends on the devices available during ofono
> startup.

Why should it be deterministic?

> 
> Furthermore, if a modem crashes and reboots while in operation, then
> udev will trigger a remove event followed by a create event, and the
> same modem will now be given a different name (as the sequence number is
> bigger).

Yes, and?

> 
> This is non suitable for systems handling several modems which want to
> identify them easily based on its path.
> 

This sounds like a very specific non-real world usecase, right?  I mean 
why don't you simply compare the IMEI if you really care?

> This patch introduces a way to be able to set persistent names for
> specific devices while still permitting previous dynamic naming
> methodology.
> 
> One can set a persistent name using udev rules for the target device
> which set the OFONO_PATHNAME env property. If ofono finds this property
> set, it will use its value as the dbus path name for the modem.

I'm hesitant to take this patch as udev logic is already complex and 
this doesn't seem to be relevant for anyone else besides your test system.

> 
> Example:
> $ cat /etc/udev/rules.d/90-local.rules
> SUBSYSTEMS=="usb", DEVPATH=="/devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.1/3-1.1.4/3-1.1.4.1/3-1.1.4.1.1", ENV{OFONO_PATHNAME}="foo"
> 
> $ udevadm info -p /devices/pci0000:00/0000:00:1a.0/usb3/3-1/3-1.1/3-1.1.4/3-1.1.4.1/3-1.1.4.1.1
> ...
> E: OFONO_PATHNAME=foo
> ...
> 
> $ mdbus2 -s org.ofono
> /
> /bluetooth
> /bluetooth/profile
> /bluetooth/profile/dun_gw
> /bluetooth/profile/hfp_ag
> /bluetooth/profile/hfp_hf
> /foo

How are you making sure that dbus path is valid?   ofono_modem_create 
can fail after all...

> /mbm_0
> ---
>   plugins/udevng.c | 22 +++++++++++++++-------
>   1 file changed, 15 insertions(+), 7 deletions(-)
> 

Regards,
-Denis