Re: About I/O callbacks ...

[Davide Libenzi <davidel@xmailserver.org>]

On 22-Jun-2001 Andi Kleen wrote:
> Davide Libenzi <davidel@xmailserver.org> writes:
> 
>> I was just thinking to implement I/O callbacks inside the kernel and test
>> which
>> kind of performance could result compared to a select()/poll()
>> implementation.
>> I prefer IO callbacks against async-io coz in this way is more direct to
>> implement an I/O driven state machine + coroutines.
>> This is a first draft :
> 
> They already exist since several years in Linux. 
> 
> It is called queued SIGIO; when you set a realtime signal
> using F_SETSIG for a fd and enable async IO. The callback is a signal
> handler or alternatively an event processing loop using sigwaitinfo*(). 
> The necessary information like which fd got an event is passed in the 
> siginfo_t. 

I know about rt signals and SIGIO :) but I can't see how You can queue signals :

current->sig->action[..]

The action field is an array so if more than one I/O notification is fired
before the SIGIO is delivered, You'll deliver only the last one.
Am I missing something ?




- Davide