Date:	Fri, 22 Jan 2010 09:39:02 +0100
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Sjur Brændeland 
	<sjur.brandeland@...ricsson.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	stefano.babic@...ic.homelinux.org, randy.dunlap@...cle.com
Subject: RE: [PATCH net-next-2.6 02/13] net-caif: add CAIF header files

Hi Sjur,

> >> +/**
> >> + * struct sockaddr_caif - the sockaddr structure for CAIF sockets.
> >> + * @u:			     Union of address data 'switched' by familty.
> >> + * @at:			     Applies when family = CAIFPROTO_AT.
> >> + * @at.type:		     Type of AT link to set up (enum caif_at_type).
> >> + * @util:		     Applies when family = CAIFPROTO_UTIL
> >> + * @util.service:	     Service name.
> >> + * @dgm:		     Applies when family = CAIFPROTO_DATAGRAM
> >> + * @dgm.connection_id:	     Datagram connection id.
> >> + * @dgm.nsapi:		     NSAPI of the PDP-Context.
> >> + * @rfm:		     Applies when family = CAIFPROTO_RFM
> >> + * @rfm.connection_id:       Connection ID for RFM.
> >> + * @rfm.volume:	     	     Volume to mount.
> >> + */
> >> +struct sockaddr_caif {
> >> +	sa_family_t  family;
> >> +	union {
> >> +		struct {
> >> +			u_int8_t  type;		/* type: enum caif_at_type */
> >> +		} at;				/* CAIFPROTO_AT */
> >> +		struct {
> >> +			char	  service[16];
> >> +		} util;				/* CAIFPROTO_UTIL */
> >> +		union {
> >> +			u_int32_t connection_id;
> >> +			u_int8_t  nsapi;
> >> +		} dgm;				/* CAIFPROTO_DATAGRAM(_LOOP)*/
> >> +		struct {
> >> +			u_int32_t connection_id;
> >> +			char	  volume[16];
> >> +		} rfm;				/* CAIFPROTO_RFM */
> >> +	} u;
> >> +};
> > 
> > as mentioned on the oFono mailing list, what is the right procedure
> > to select a local CAIF device for usage with doing bing(). The use
> > case I am thinking of is that you have multiple CAIF device attached
> > to the same system. Think of desktops with USB or even Dual-SIM
> > phones. Before we set the API in stone, we need to have a way o bind
> > the socket to a specific device. Maybe it is possible, but I am
> > missing it.      
> 
> The CAIF interface can be selected by using the following types:
> [snip caif_config.h]
> /**
>  * enum caif_phy_preference  - Types of physical HW interfaces
>  *				       towards modem defined in CAIF stack
>  * @CAIF_PHYPREF_UNSPECIFIED:	Default physical interface
>  * @CAIF_PHYPREF_LOW_LAT:	Default physical interface for low-latency
>  *				      traffic
>  * @CAIF_PHYPREF_HIGH_BW:	Default physical interface for high-bandwidth
>  *				      traffic
>  * @CAIF_PHYPREF_LOOP:		TEST Loopback interface, simulating modem
>  *				      responses
>  *
>  * For client convenience, two special types are defined:
>  * CAIF_PHYPREF_LOW_LAT is the preferred low-latency physical link.
>  * Typically used for "control" purposes.
>  * CAIF_PHYPREF_HIGH_BW is the preferred high-bandwidth physical link.
>  * Typically used for "payload" purposes.
>  */
> ...
> enum caif_phy_preference {
> 	CAIF_PHYPREF_UNSPECIFIED,
> 	CAIF_PHYPREF_LOW_LAT,
> 	CAIF_PHYPREF_HIGH_BW,
> 	CAIF_PHYPREF_LOOP
> };
> [snip caif_socket.h]
> ...
> /**
>  * struct caif_channel_opt - CAIF channel connect options.
>  * @priority:		Priority of the channel (between 0 and 0x1f)
>  * @link_selector:	Selector for the physical link.
>  *			      (see enum caif_phy_preference in caif_config.h)
>  * @link_name:		Physical link to use. This is the instance name of the
>  *			      CAIF Physical Driver.
>  */
> struct caif_channel_opt {
> 	u_int16_t  priority;
> 	u_int16_t  link_selector;
> 	char	   link_name[16];
> };
> ...
> /** enum caif_socket_opts - CAIF option values for getsockopt and setsockopt
>  * @CAIFSO_CHANNEL:		Used to set the connect options on a CAIF
>  *				socket. (struct caif_config_opt). This can only
>  *				be set before connecting.
> [end snip]
> 
> CAIFSO_CHANNEL is used for specifying the physical interface to use for the 
> CAIF Channel. You can select the type of interface to use
> by setting link_selector:
> CAIF_PHYPREF_LOW_LAT will typically be used for AT (or other control traffic),
> and CAIF_PHYPREF_HIGH_BW for IP traffic.
> When the CAIF interfaces registers itself it will inform about their type,
> (low-latency or high-bandwidth). This approach assumes that you have only one
> modem, but multiple links to it (e.g. USB and UART). 
> 
> But you can also specify interface by name using link_name. In this case
> you specify the name of the interface to use. I think this would support
> your use case with multiple modems attached.

sounds good, but why using a socket option and not allowing to just use
bind(). Maybe it is just my personal preference, because I am used to do
it like this for TCP and Bluetooth.

Regards

Marcel


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