Re: [dpdk-stable] [PATCH v2] net/virtio: add Tx preparation

[Tiwei Bie <tiwei.bie@intel.com>]

On Wed, Jun 05, 2019 at 10:28:14AM +0300, Andrew Rybchenko wrote:
> Hi,
> 
> On 6/5/19 4:41 AM, Tiwei Bie wrote:
> 
>     Hi,
> 
>     Thanks for the patch!
> 
> 
> More will follow. At least Tx checksum offload is broken when used together
> with VLAN insertion since the later prepend to mbuf, but do nothing with
> l2_len/outer_l2_len. We'll send a patch to move rte_vlan_insert()
> to Tx prepare and suggest separate patch to update l2_len or outer_l2_len
> when software VLAN insertion is done.
> 

Thanks :)

> 
>     On Mon, Jun 03, 2019 at 07:50:05PM +0100, Andrew Rybchenko wrote:
>     [...]
> 
>          uint16_t
>         +virtio_xmit_pkts_prepare(void *tx_queue __rte_unused, struct rte_mbuf **tx_pkts,
>         +                       uint16_t nb_pkts)
>         +{
>         +       uint16_t nb_tx;
>         +       int error;
>         +
>         +       for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
>         +               struct rte_mbuf *m = tx_pkts[nb_tx];
>         +
>         +#ifdef RTE_LIBRTE_ETHDEV_DEBUG
>         +               error = rte_validate_tx_offload(m);
>         +               if (unlikely(error)) {
>         +                       rte_errno = -error;
>         +                       break;
>         +               }
>         +#endif
>         +
>         +               error = rte_net_intel_cksum_prepare(m);
>         +               if (unlikely(error)) {
>         +                       rte_errno = -error;
> 
>     It's a bit confusing here.
>     Based on the API doc of rte_eth_tx_prepare():
> 
>     https://github.com/DPDK/dpdk/blob/7f9f46d6cef5b03681a3935b9a18378e08ca6f62/lib/librte_ethdev/rte_ethdev.h#L4360-L4362
> 
>     It should set negative value to rte_errno when error happens,
> 
> 
> I'm pretty sure that it is a bug in documentation. rte_errno must be positive.

Yeah. Negative rte_errno looks confusing.

> I'll send a patch to fix it.
> Even the code just below sets positive rte_errno. Simple cases are very easy to
> find:
> $ git grep 'rte_errno = E' | wc -l
> 557
> $ git grep 'rte_errno = -E' | wc -l
> 50
> 
> A bit more complex cases which require careful review:
> $ git grep -e 'rte_errno = -[a-z]' | wc -l                                     
> 37
> $ git grep -e 'rte_errno = [a-z]' | wc -l
> 150
> 
> Cases which look right from the first sight overweight wrong 3 times.
> But it is still too many cases which are potentially wrong.
> 
> Andrew.

Thanks,
Tiwei