linux-kernel - RE: [EXT] Re: [PATCH v4 1/2] net: page_pool: export page_pool

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Message-ID: <PAXPR04MB9185330823A685659C53AA6D89049@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date:   Tue, 15 Nov 2022 17:52:20 +0000
From:   Shenwei Wang <shenwei.wang@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>
Subject: RE: [EXT] Re: [PATCH v4 1/2] net: page_pool: export page_pool_stats
 definition



> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: Tuesday, November 15, 2022 11:43 AM
> To: Shenwei Wang <shenwei.wang@....com>
> Cc: David S. Miller <davem@...emloft.net>; Eric Dumazet
> <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo Abeni
> <pabeni@...hat.com>; Jesper Dangaard Brouer <hawk@...nel.org>; Ilias
> Apalodimas <ilias.apalodimas@...aro.org>; Alexei Starovoitov
> <ast@...nel.org>; Daniel Borkmann <daniel@...earbox.net>; John Fastabend
> <john.fastabend@...il.com>; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; imx@...ts.linux.dev
> Subject: Re: [EXT] Re: [PATCH v4 1/2] net: page_pool: export page_pool_stats
> definition
> 
> Caution: EXT Email
> 
> > > I agree the API is broken, but i think there is a better fix.
> > >
> > > There should be a stub of page_pool_get_stats() for when
> > > CONFIG_PAGE_POOL_STATS is disabled.
> > >
> > > Nothing actually dereferences struct page_pool_stats when you have this
> stub.
> > > So it might be enough to simply have
> > >
> > > struct page_pool_stats{
> > > };
> > >
> >
> > As the structure is open when the CONFIG_PAGE_POOL_STATS is enabled,
> > you can not prevent a user to access its members. The empty stub will
> > still have problems in this kind of situations.
> 
> The users, i.e. the driver, has no need to access its members. The members can
> change, new ones can be added, and it will not cause a problem, given the way
> this API is defined. Ideally, page_pool_stats would of been an opaque cookie,
> but that is not how it was implemented :-(
> 

Okay if the assumption is the user would never access its members.

Regards,
Shenwei

>             Andrew