qmi_wwan add_mux/del_mux

[Daniele Palmas]

Hi Aleksander,

Il giorno gio 21 gen 2021 alle ore 17:45 Aleksander Morgado
<aleksander at aleksander.es> ha scritto:
>
> Hey Daniele,
>
> Say I create a new muxed interface for mux id 5:
>   echo 5 > /sys/class/net/wwan0/qmi/add_mux
> A new qmimux0 interface is created.
>
> Is there any way to know which mux id was used to create the qmimux0
> looking just at sysfs or some other way? In other words, how would I
> know what the mux id is for a given qmimuxN interface that may not
> have been created by me?
>
> Also, say that I have 2 different programs creating this kind of
> interfaces, and both use the qmi/add_mux attribute. If they both run
> at the same time (asking for different mux ids), and two interfaces
> qmimux0 and qmimux1 are created, how can each program know which was
> the interface corresponding to the mux id they requested?
>
> Not sure I'm missing something, but I didn't find a way to do this
> kind of matchings. If the virtual qmimux interface exposed a sysfs
> attribute specifying which is the mux id they correspond to, the
> matching would be much easier. Would that be possible?
>

Yes, all your questions make sense to me and, to my understanding,
currently there's no solution at the driver level.

As you sugget, the easiest change would probably be a sysfs file in
the qmimux network interface: I quickly wrote the attached patch,
without claiming to be correct, just to give the idea (applies to
current net-next).

So it works something like:

root at LABNL-ITC-SW01:~# ip link show
7: wwp0s20u2i2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
mode DEFAULT group default qlen 1000
    link/ether 5e:1a:7e:1c:86:d4 brd ff:ff:ff:ff:ff:ff
root at LABNL-ITC-SW01:~# echo 5 >
/sys/bus/usb/devices/3-2:1.2/net/wwp0s20u2i2/qmi/add_mux
root at LABNL-ITC-SW01:~# echo 9 >
/sys/bus/usb/devices/3-2:1.2/net/wwp0s20u2i2/qmi/add_mux
root at LABNL-ITC-SW01:~# ip link show
7: wwp0s20u2i2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
mode DEFAULT group default qlen 1000
    link/ether 5e:1a:7e:1c:86:d4 brd ff:ff:ff:ff:ff:ff
8: qmimux0: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state
DOWN mode DEFAULT group default qlen 1000
    link/none
9: qmimux1: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state
DOWN mode DEFAULT group default qlen 1000
    link/none
root at LABNL-ITC-SW01:~# cat
/sys/bus/usb/devices/3-2:1.2/net/wwp0s20u2i2/upper_qmimux0/qmap/mux_id
0x05
root at LABNL-ITC-SW01:~# cat
/sys/bus/usb/devices/3-2:1.2/net/wwp0s20u2i2/upper_qmimux1/qmap/mux_id
0x09

However, I'm not sure this is the best solution and would be accepted,
since there's reluctance to add new sysfs files.

Bjørn, do you have any hint to point us to the right direction?

Regards,
Daniele

> For context, I'm trying to work on adding support for this interface
> in libqmi, with the new qmi_device_add_link() interface that is right
> now only available when using rmnet with netlink.
>
> --
> Aleksander
> https://aleksander.es
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