Re: [Fwd: Re: connector is missing in 2.6.12-rc2-mm1]

[Evgeniy Polyakov <johnpol@2ka.mipt.ru>]

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On Thu, 2005-04-07 at 12:41 +0200, Kay Sievers wrote:
> On Thu, 2005-04-07 at 13:52 +0400, Evgeniy Polyakov wrote:
> > On Thu, 2005-04-07 at 10:12 +0100, Ian Campbell wrote:
> > > On Thu, 2005-04-07 at 12:13 +0400, Evgeniy Polyakov wrote:
> > > > The main idea was to simplify userspace control and notification
> > > > system - so people did not waste it's time learning how skb's are
> > > > allocated
> > > > and processed, how socket layer is designed and what all those
> > > > netlink_* and NLMSG* mean if they do not need it.
> > > 
> > > Isn't connector built on top of netlink? If so, is there any reason for
> > > it to be a new subsystem rather than an extension the the netlink API?
> > 
> > Connector is not netlink API extension in any way.
> > It uses netlink as transport layer, one can change
> > cn_netlink_send()/cn_input() 
> > into something like bidirectional ioctl and use it.
> > 
> > Only one cn_netlink_send() function can be "described" as API
> > extension, 
> > although even it is not entirely true.
> 
> I see much overlap here too. Wouldn't it be nice to see the transport
> part of the connector code to be implemented as a generic netlink
> multicast? We already have uni- and broadcast for netlink.

Netlink broadcast is multicast actually,
if listener exists, then message will be sent to him, 
if no - skb will be just freed.

> Isn't the whole purpose of the connector to hook in notifications that
> act only if someone is listening? That is a perfect multicast case. :)

Connector can be used to send data from userspace to kernelspace,
so it allows sending controlling messages without ioctl() compatibility 
mess and so on.

One may use cn_netlink_send() to send notification without being
registered 
in connector, if it's second parameter is 0, then appropriate 
connector listener will be searched for.

It is different from netlink messages, 
netlink is a transport layer for connector.

> At the time we added kobject_uevent I was missing something like this.
> The broadcast groups did not really fit, and we decided not to use them,
> and unicast wasn't a option here.

There is a check for listener in netlink_broadcast() - sk_for_each_bound
().

> Thanks,
> Kay
-- 
        Evgeniy Polyakov

Crash is better than data corruption -- Arthur Grabowski

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