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From: Stephen Hemminger <stephen@networkplumber.org>
To: Shahaf Shuler <shahafs@mellanox.com>
Cc: Thomas Monjalon <thomas@monjalon.net>,
	"olivier.matz@6wind.com" <olivier.matz@6wind.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] mbuf: extend pktmbuf pool private structure
Date: Wed, 20 Nov 2019 07:56:14 -0800
Message-ID: <20191120075614.07bf2207@hermes.lan> (raw)
In-Reply-To: <AM0PR0502MB3795933B2398576A4CBE997CC34F0@AM0PR0502MB3795.eurprd05.prod.outlook.com>

On Wed, 20 Nov 2019 07:01:26 +0000
Shahaf Shuler <shahafs@mellanox.com> wrote:

> Wednesday, November 20, 2019 1:51 AM, Stephen Hemminger:
> > Subject: Re: [dpdk-dev] [PATCH] mbuf: extend pktmbuf pool private
> > structure
> > 
> > On Tue, 19 Nov 2019 23:30:15 +0100
> > Thomas Monjalon <thomas@monjalon.net> wrote:
> >   
> > > 19/11/2019 17:25, Stephen Hemminger:  
> > > > On Tue, 19 Nov 2019 15:23:50 +0000
> > > > Shahaf Shuler <shahafs@mellanox.com> wrote:
> > > >  
> > > > > Tuesday, November 19, 2019 11:33 AM, Thomas Monjalon:  
> > > > > > Subject: Re: [PATCH] mbuf: extend pktmbuf pool private structure
> > > > > >
> > > > > > 18/11/2019 11:02, Shahaf Shuler:  
> > > > > > >  struct rte_pktmbuf_pool_private {
> > > > > > >  	uint16_t mbuf_data_room_size; /**< Size of data space in  
> > each  
> > > > > > mbuf. */  
> > > > > > >  	uint16_t mbuf_priv_size;      /**< Size of private area in each  
> > mbuf.  
> > > > > > */  
> > > > > > > +	uint32_t reserved; /**< reserved for future use. */  
> > > > > >
> > > > > > Maybe simpler to give the future name "flags" and keep the  
> > comment  
> > > > > > "reserved for future use".  
> > > > >
> > > > > I'm am OK w/ changing to flags.
> > > > > If Olivier accepts maybe you can change while applying?  
> > > >
> > > > After the Linux openat experience if you want to add flags.
> > > > Then all usage of API needs to validate that flags is 0.  
> > >
> > > Sorry Stephen, I don't understand what you mean.
> > > Please could you explain?
> > >
> > >  
> > 
> > Any time a new field is added that maybe used later you can not guarantee
> > that existing code correctly initializes the value to zero. What happened with
> > openat() was that there was a flag value that was originally unused, but since
> > kernel did not enforce that it was zero; it could not later be used for
> > extensions.
> > 
> > You need to make sure that all reserved fields are initialized.
> > That means when a private pool is created it is zeroed. And if a flag is new
> > argument to an API, check for zero at create time.  
> 
> I guess we can hard code the value for 0 on the rte_pktmbuf_pool_create function and have some assert on the rte_pktmbuf_pool_init callback (we cannot fail as this function returns void).
> Any other places you find problematic? 

No. that should be good. 

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-18 10:02 Shahaf Shuler
2019-11-18 16:12 ` Stephen Hemminger
2019-11-19  6:35   ` Shahaf Shuler
2019-11-19  9:32 ` Thomas Monjalon
2019-11-19 15:23   ` Shahaf Shuler
2019-11-19 16:25     ` Stephen Hemminger
2019-11-19 22:30       ` Thomas Monjalon
2019-11-19 23:50         ` Stephen Hemminger
2019-11-20  7:01           ` Shahaf Shuler
2019-11-20 15:56             ` Stephen Hemminger [this message]
2019-11-21 14:15               ` Olivier Matz
2019-11-21 12:28 ` [dpdk-dev] [PATCH v2] " Shahaf Shuler
2019-11-21 14:31   ` Olivier Matz
2019-11-24  5:52     ` Shahaf Shuler
2019-11-24  5:53   ` [dpdk-dev] [PATCH v3] " Shahaf Shuler
2019-11-24 17:50     ` Stephen Hemminger
2019-11-24 18:05       ` Thomas Monjalon
2019-11-24 18:10         ` Shahaf Shuler
2019-11-25  8:12     ` Olivier Matz
2019-11-25 10:21     ` [dpdk-dev] [PATCH v4] " Shahaf Shuler
2019-11-25 10:27       ` Olivier Matz
2019-11-25 21:42         ` Thomas Monjalon

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