linux-kernel - Re: [PATCH net-next v18 07/14] memory-provider: dmabuf devmem memory provider

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Message-ID: <6a779dbb-ad3a-47cf-bb8e-1a50732a9694@gmail.com>
Date: Tue, 13 Aug 2024 16:11:15 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
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Subject: Re: [PATCH net-next v18 07/14] memory-provider: dmabuf devmem memory
 provider

On 8/13/24 15:39, Jakub Kicinski wrote:
> On Tue, 13 Aug 2024 03:31:13 +0100 Pavel Begunkov wrote:
>> I'm getting lost, so repeating myself a bit. What I think
>> would be a good approach is if we get an error back from
>> the driver if it doesn't support netiov / providers.
>>
>> netdev_rx_queue_restart() {
>> 	...
>> 	err = dev->queue_mgmt_ops->ndo_queue_mem_alloc();
>> 	if (err == -EOPNOTSUPP) // the driver doesn't support netiov
>> 		return -EOPNOTSUPP;
>> 	...
>> }
>>
>> That can be done if drivers opt in to support providers,
>> e.g. via a page pool flag.
>>
>> What I think wouldn't be a great option is getting back a
>> "success" from the driver even though it ignored
> 
> page pool params are not the right place for a supported flag.
> Sooner or later we'll want to expose this flag to user space.

Fair enough, it appeared to me that's what you was suggesting

"What comes to mind is adding an "I can gobble up net_iovs from this
pool" flag in page pool params (the struct that comes from the driver),
and then on the installation path we can check ..."

We can also move it from pp flags to queue API callbacks, however if we
want to expose it to the userspace, I'd imagine we need a queue flag set
by the driver, which then can be queried by netlink or whichever
interface is appropriate. And it can be used can be used to fail
netdev_rx_queue_restart() for queues/drivers that don't support mp.

netdev_rx_queue_restart() {
	if (rxq->mp_params && !rxq->netiov_supported)
		fail;
}

Perhaps, I don't understand what approach you contemplate, but
maybe Mina has cracked it.

-- 
Pavel Begunkov