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

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Date:   Tue, 15 Nov 2022 18:43:05 +0100
From:   Andrew Lunn <andrew@...n.ch>
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" <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

> > 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 :-(

	    Andrew