[cgl_discussion] Re: alternate event logging proposal

[Tim Hockin]

Jeff Garzik wrote:
> Brad Hards wrote:
> 
>> I liked the /sbin/hotplug arrangement (aka call_usermode_helper). In 
>> fact, my plan was to add the call_usermode_helper call to the 
>> netif_carrier_[on,off] functions. Unfortuantely, I've been to too many 
>> of Rusty's talks, and know that calling a function that is only safe 
>> in user context is unlikely to be a good idea in 
>> netif_carrier_[on,off], which are more than likely running in 
>> interrupt context.
> 
> 
> 
> You really want something where a userspace app can sleep on an fd, to 
> be awakened when link changes (or some other interesting event occurs)

I tend to agree - I like either of the models:

a bunch of little single-value files that can be polled and read

  or

a single device_event file that a daemon reads and dispatches events (I 
like this one because the daemon is already written, just poorly named - 
acpid)

For things like netif_carrier, poll() is probably best - the DHCP client 
can be fully self contained, and not need an eventd to alert it to a 
signal change.  Of course, acpid does support UNIX socket connections 
from apps like DHCP....



-- 
Tim Hockin
Systems Software Engineer
Sun Microsystems, Linux Kernel Engineering
thockin at sun.com