netmap extra rings and buffers

[Eggert, Lars]

Thank you!

On 2014-9-4, at 17:48, Luigi Rizzo <rizzo at iet.unipi.it> wrote:

> On Thu, Sep 04, 2014 at 11:58:28AM +0000, Eggert, Lars wrote:
>> Hi Luigi,
>> 
>> I'm allocating extra rings and/or extra buffers via the nr_arg1/nr_arg3 parameters for NIOCREGIF.
>> 
>> Once I've done that, how do I actually access those rings and buffers?
>> 
>> For extra rings, the documentation and example code don't really say anything.
>> 
>> For extra buffers, the documentation says "nifp->ni_bufs_head will be the index of the first buffer" but doesn't really explain how I can find the buffer given its index (since it's not in a ring, the NETMAP_BUF macro doesn't seem to apply?) The part about "buffers are linked to each other using the first uint32_t as the index" is also unclear to me.
>> 
>> Do you have some more text or example code that shows how to use extra rings and buffers?
> 
> the ifield to request extra rings is only important when you want
> to make sure that the memory region for a VALE port has also
> space to host some pipes. Otherwise, for physical ports (which at
> the moment all share the same address space) there is not a real
> need to specify it.
> 
> For the extra buffers, remember that NETMAP_BUF() can translate
> buffer indexes for any netmap buffer, even those not in a ring.
> All it does is grab the base address of the buffer pool from the
> ring, and add the buffer index times the buffer size.
> 
> So you can navigate the pool of extra buffers as follows
> 
>    uint32_t x = nifp->ni_bufs_head;	// index of first buf
> 
>    void *p = NETMAP_BUF(any_ring, x);	// address of the first buffer
> 
>    x = *((uint32_t *)p);		// index of the next buffer
> 
> cheers
> luigi

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