netdev - Re: [PATCH 14/18] netmem: use _Generic to cover const casting for page_to

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Message-ID: <CAHS8izMRDixoLC5p1+h4oxrfVvErXcokR6qC_zuOqBredBBMbA@mail.gmail.com>
Date: Fri, 23 May 2025 10:14:54 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Byungchul Park <byungchul@...com>
Cc: willy@...radead.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, kernel_team@...ynix.com, kuba@...nel.org, 
	ilias.apalodimas@...aro.org, harry.yoo@...cle.com, hawk@...nel.org, 
	akpm@...ux-foundation.org, davem@...emloft.net, john.fastabend@...il.com, 
	andrew+netdev@...n.ch, asml.silence@...il.com, toke@...hat.com, 
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	rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, horms@...nel.org, 
	linux-rdma@...r.kernel.org, bpf@...r.kernel.org, vishal.moola@...il.com
Subject: Re: [PATCH 14/18] netmem: use _Generic to cover const casting for page_to_netmem()

On Thu, May 22, 2025 at 8:26 PM Byungchul Park <byungchul@...com> wrote:
>
> The current page_to_netmem() doesn't cover const casting resulting in
> trying to cast const struct page * to const netmem_ref fails.
>
> To cover the case, change page_to_netmem() to use macro and _Generic.
>
> Signed-off-by: Byungchul Park <byungchul@...com>

Reviewed-by: Mina Almasry <almasrymina@...gle.com>

> ---
>  include/net/netmem.h | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 29c005d70c4f..c2eb121181c2 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -172,10 +172,9 @@ static inline netmem_ref net_iov_to_netmem(struct net_iov *niov)
>         return (__force netmem_ref)((unsigned long)niov | NET_IOV);
>  }
>
> -static inline netmem_ref page_to_netmem(struct page *page)
> -{
> -       return (__force netmem_ref)page;
> -}
> +#define page_to_netmem(p)      (_Generic((p),                  \
> +       const struct page *:    (__force const netmem_ref)(p),  \
> +       struct page *:          (__force netmem_ref)(p)))
>
>  static inline netmem_ref alloc_netmems_node(int nid, gfp_t gfp_mask,
>                 unsigned int order)
> --
> 2.17.1
>


-- 
Thanks,
Mina