Re: [dpdk-dev] [PATCH BUG 335 3/3] net/virtio: fix compilation error with 0 headroom

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 8/1/19 10:09 AM, Hemant Agrawal wrote:
> HI,
>> On 7/26/19 2:25 PM, Olivier Matz wrote:
>>> Hi,
>>>
>>> On Thu, Jul 25, 2019 at 04:36:45PM +0530, Hemant Agrawal wrote:
>>>> When using RTE_PKTMBUF_HEADROOM as 0, virito ethdev driver throws
>>>> compilation error
>>>> virtio_ethdev.c:1851:2: note: in expansion of macro ‘RTE_BUILD_BUG_ON’
>>>> RTE_BUILD_BUG_ON(RTE_PKTMBUF_HEADROOM
>>>> 	< sizeof(struct virtio_net_hdr_mrg_rxbuf));
>>>>
>>>> This patch change it into run-time check.
>>>> Reported as:
>>>>
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbug
>>>>
>> s.dpdk.org%2Fshow_bug.cgi%3Fid%3D335&amp;data=02%7C01%7Chemant.
>> agrawa
>>>>
>> l%40nxp.com%7C303b7755f6ff4c44721a08d714f2cbb5%7C686ea1d3bc2b4c6
>> fa92c
>>>>
>> d99c5c301635%7C0%7C0%7C637000905339982654&amp;sdata=oQ4b4TZ36x
>> WiHOtKE
>>>> %2BwCZfy2ND%2FgP%2FESfGL%2FEdoJbYI%3D&amp;reserved=0
>>>>
>>>> Fixes: 198ab33677c9 ("net/virtio: move device initialization in a
>>>> function")
>>>
>>> I think the proper commit is:
>>> Fixes: dec08c28c0b3 ("virtio: check packet headroom at compile time")
>>
>> Indeed.
>>
>>> It looks this patch more or less reverts this old commit.
>>> +CC Stephen
>>
>> I wonder whether we could have a warning at build time so that the one who
>> builds DPDK is aware some driver may not be usable, in addition to the
>> below patch that fails virtio-net init.
> 
> [Hemant] I will also prefer compile time check instead of run-time check for any non-default configs.
> If someone is modifying the config, he can very well disable the drivers, which don't like those settings. 
> 
> However, earlier discussion w.r.t this bug moved in other direction to make DPDK compliable for all cases and allow regress testing.

Ok, I don't have a strong opinion on this, so feel free to apply this
patch as is. We can add a build-ime warning later if we find it useful.

Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime

> 
>>
>> Any thoughts?
>>
>> Thanks,
>> Maxime
>>
>>>> Cc: stable@dpdk.org
>>>> Cc: Olivier Matz <olivier.matz@6wind.com>
>>>>
>>>> Signed-off-by: Hemant Agrawal <hemant.agrawal@nxp.com>
>>>> ---
>>>>   drivers/net/virtio/virtio_ethdev.c | 9 ++++++++-
>>>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/virtio/virtio_ethdev.c
>>>> b/drivers/net/virtio/virtio_ethdev.c
>>>> index 62c827443..3e2e8bd2a 100644
>>>> --- a/drivers/net/virtio/virtio_ethdev.c
>>>> +++ b/drivers/net/virtio/virtio_ethdev.c
>>>> @@ -1848,7 +1848,14 @@ eth_virtio_dev_init(struct rte_eth_dev
>> *eth_dev)
>>>>   	struct virtio_hw *hw = eth_dev->data->dev_private;
>>>>   	int ret;
>>>>
>>>> -	RTE_BUILD_BUG_ON(RTE_PKTMBUF_HEADROOM < sizeof(struct
>> virtio_net_hdr_mrg_rxbuf));
>>>> +	if (sizeof(struct virtio_net_hdr_mrg_rxbuf) >
>> RTE_PKTMBUF_HEADROOM) {
>>>> +		PMD_INIT_LOG(ERR,
>>>> +			"Not sufficient headroom required = %d, avail = %d",
>>>> +			(int)sizeof(struct virtio_net_hdr_mrg_rxbuf),
>>>> +			RTE_PKTMBUF_HEADROOM);
>>>> +
>>>> +		return -1;
>>>> +	}
>>>>
>>>>   	eth_dev->dev_ops = &virtio_eth_dev_ops;
>>>>
>>>> --
>>>> 2.17.1
>>>>
>>>