[LEDE-DEV] Help me understand ubus extensions via C api

[Carlito Nueno]

Thanks Alexandru!

That was very helpful. Now I have a better understanding of the ubus structure.

Few more questions:

- when/where does this ubus.c file (executable?) run?
- how these functions used? when are they called? starting from line
42 to line 47 (https://github.com/lede-project/source/blob/master/package/network/services/hostapd/src/src/ap/ubus.h#L42)

Thanks again.

On Wed, Jul 5, 2017 at 11:54 PM, Alexandru Ardelean
<ardeleanalex at gmail.com> wrote:
> On Thu, Jul 6, 2017 at 4:31 AM, Carlito Nueno <carlitonueno at gmail.com> wrote:
>> Hi all,
>>
>> I want to customize a small feature in how hostapd responds to probe
>> request and I was looking at
>> https://github.com/lede-project/source/blob/master/package/network/services/hostapd/src/src/ap/ubus.c
>>
>> Please help me understand how it works? for example when I call `ubus
>> call hostapd.wlan0-1 del_client "{....}" what happens?
>
> the `ubus` cli will talk to ubusd
> ubusd is the broker [or hub] for all things ubus between all processes
> [that register with ubus[d] ]
>
> hostapd has registered the `hostapd.wlan0-1` ubus object here
> https://github.com/lede-project/source/blob/master/package/network/services/hostapd/src/src/ap/ubus.c#L457
> via the ubus_add_object()
>
> all registration to ubusd is done via libubus, which abstracts a lot
> of the stuff to connect/talk to ubusd
> all that you need to use [in a daemon/process with ubus] is in
> libubus.h ; that header is exported at build time for other modules to
> use
> http://git.openwrt.org/?p=project/ubus.git;a=blob;f=libubus.h;h=4e45cb620a28befe23c27d3b8dc7eb1a1d12fb1a;hb=HEAD
>
> it's important that all operations to ubus[d] be done on a
> ubus_context object, which is a wrapper struct for a socket FD, some
> buffer data, and other stuff
>
> [ well, this was mostly ubus internals [in case it interests you ] ]
>
>>
>> I know that ubus_cli
>> (http://git.openwrt.org/?p=project/ubus.git;a=blob;f=cli.c;h=19ccbb5093ce4c326010a9b2f504d7cd50798275;hb=HEAD)
>> parses the input but how does ubus call the functions inside the above
>> file (the ubus.c, ubus hostapd extension)?
>
> the ubus cli tool uses libubus
> but the code for cli, may not be a sufficient example to do other
> operations [like in hostapd ]
>
>>
>> I see that there is this function, but how is that called
>>
>> static int hostapd_bss_del_client(struct ubus_context *ctx, struct
>> ubus_object *obj, struct ubus_request_data *req, const char *method,
>> struct blob_attr *msg);
>>
>
> Coming back to your "I want to customize a small feature in how hostapd"
> I think that all you might need to do is register a new function here:
> https://github.com/lede-project/source/blob/master/package/network/services/hostapd/src/src/ap/ubus.c#L419
> or extend an existing one.
>
> As I mentioned, the ubus cli talks to ubusd.
> When doing `ubus call hostapd.wlan0-1 del_client "{....}"` , this
> means that hostapd has already registered a ` hostapd.wlan0-1` with
> ubusd
> When you call "del_client", the hostapd_bss_del_client() callback will
> be called [ubus cli will ask ubusd to access del_client from
> hostapd.wlan0-1 ] , but before that, the `del_policy` object will be
> used to validate the message format.
> [ You may have noticed that some callbacks are UBUS_METHOD_NOARG() and
> some are UBUS_METHOD() ; the ones without a policy arg will get
> processed without any msg format validation ]
>
>>
>> Thank you!
>>
>
> Maybe this information was not too well structured.
> But hope it helps.
>
>> _______________________________________________
>> Lede-dev mailing list
>> Lede-dev at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/lede-dev