[dpdk-dev] [PATCH v12 0/3] mempool: add external mempool manager

[Olivier MATZ]

Hi,

On 06/15/2016 01:47 PM, Hunt, David wrote:
>
>
> On 15/6/2016 11:13 AM, Jan Viktorin wrote:
>> Hi,
>>
>> I've got one last question. Initially, I was interested in creating
>> my own external memory provider based on a Linux Kernel driver.
>> So, I've got an opened file descriptor that points to a device which
>> can mmap a memory regions for me.
>>
>> ...
>> int fd = open("/dev/uio0" ...);
>> ...
>> rte_mempool *pool = rte_mempool_create_empty(...);
>> rte_mempool_set_ops_byname(pool, "uio_allocator_ops");
>>
>> I am not sure how to pass the file descriptor pointer. I thought it would
>> be possible by the rte_mempool_alloc but it's not... Is it possible
>> to solve this case?
>>
>> The allocator is device-specific.
>>
>> Regards
>> Jan
>
> This particular use case is not covered.
>
> We did discuss this before, and an opaque pointer was proposed, but did
> not make it in.
> http://article.gmane.org/gmane.comp.networking.dpdk.devel/39821
> (and following emails in that thread)
>
> So, the options for this use case are as follows:
> 1. Use the pool_data to pass data in to the alloc, then set the
> pool_data pointer before coming back from alloc. (It's a bit of a hack,
> but means no code change).
> 2. Add an extra parameter to the alloc function. The simplest way I can
> think of doing this is to
> take the *opaque passed into rte_mempool_populate_phys, and pass it on
> into the alloc function.
> This will have minimal impact on the public API,s as there is already an
> opaque there in the _populate_ funcs, we're just
> reusing it for the alloc.
>
> Do others think option 2 is OK to add this at this late stage? Even if
> the patch set has already been ACK'd?

Jan's use-case looks to be relevant.

What about changing:

   rte_mempool_set_ops_byname(struct rte_mempool *mp, const char *name)

into:

  rte_mempool_set_ops(struct rte_mempool *mp, const char *name,
     void *opaque)

?

The opaque pointer would be saved in mempool structure, and used
when the mempool is populated (calling mempool_ops_alloc).
The type of the structure pointed by the opaque has to be defined
(and documented) into each mempool_ops manager.


Olivier