RE: [PATCH v1] net/vhost: clear data of packet mbuf after sending pkts

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Zhang, Yuying <yuying.zhang@intel.com>
> Sent: Wednesday, March 2, 2022 4:59 PM
> To: David Marchand <david.marchand@redhat.com>
> Cc: dev <dev@dpdk.org>; Maxime Coquelin <maxime.coquelin@redhat.com>; Xia,
> Chenbo <chenbo.xia@intel.com>; dpdk stable <stable@dpdk.org>;
> stephen@networkplumber.org
> Subject: RE: [PATCH v1] net/vhost: clear data of packet mbuf after sending
> pkts
> 
> Hi Marchand,
> 
> > -----Original Message-----
> > From: David Marchand <david.marchand@redhat.com>
> > Sent: Tuesday, March 1, 2022 5:48 PM
> > To: Zhang, Yuying <yuying.zhang@intel.com>
> > Cc: dev <dev@dpdk.org>; Maxime Coquelin <maxime.coquelin@redhat.com>;
> > Xia, Chenbo <chenbo.xia@intel.com>; dpdk stable <stable@dpdk.org>
> > Subject: Re: [PATCH v1] net/vhost: clear data of packet mbuf after sending
> pkts
> >
> > On Tue, Mar 1, 2022 at 10:02 AM Zhang, Yuying <yuying.zhang@intel.com>
> > wrote:
> 
> ...
> 
> > >
> > > eth_vhost_tx() frees the packet mbuf back into its original mempool every
> > time after a packet sent without clearing the data field.
> > > Then packet transmit  function will get bulk directly without reset. New
> > generated packet contains old data of previous packet. This is wrong.
> >
> > With the proposed patch, if the mbuf refcnt is != 0, you are shooting the
> data
> > while some other part of the application might be needing it.
> >
> > Plus, there should be no expectation about a mbuf data content when
> retrieving
> > one from a mempool.
> > The only bytes that are guaranteed to be initialised by the mbuf API are its
> > metadata.
> >
> >
> > If there is an issue somewhere in dpdk where the mbuf data content is
> expected
> > to be 0 on allocation, please point at it.
> > Or share the full test that failed.
> 
> According to the test_plan guide of dpdk
> (https://doc.dpdk.org/dts/test_plans/loopback_virtio_user_server_mode_test_pla
> n.html),
> Test Case 13 (loopback packed ring all path payload check test using server
> mode and multi-queues), the payload of each packet must be the same.
> The packet of first stream is initialized value 0. Then this packet is put
> back into mempool(actually, the local cache of the core).
> The packet of rest stream is got from local_cache directly and contains the
> first packet's header data in the payload. Therefore, the payload of the
> packets
> are different.

Could you explain more about the problem?

But anyway I think this fix is wrong. After we're clear about the problem,
there should be another solution.

Thanks,
Chenbo

> 
> >
> >
> > --
> > David Marchand