linux-kernel - Re: [PATCH 04/26] net: add a new sockptr

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Date:   Thu, 23 Jul 2020 09:40:27 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        linux-sctp@...r.kernel.org, linux-hams@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, bridge@...ts.linux-foundation.org,
        linux-can@...r.kernel.org, dccp@...r.kernel.org,
        linux-decnet-user@...ts.sourceforge.net,
        linux-wpan@...r.kernel.org, linux-s390@...r.kernel.org,
        mptcp@...ts.01.org, lvs-devel@...r.kernel.org,
        rds-devel@....oracle.com, linux-afs@...ts.infradead.org,
        tipc-discussion@...ts.sourceforge.net, linux-x25@...r.kernel.org
Subject: Re: [PATCH 04/26] net: add a new sockptr_t type

On Wed, Jul 22, 2020 at 11:09 PM Christoph Hellwig <hch@....de> wrote:
>
> Add a uptr_t type that can hold a pointer to either a user or kernel
> memory region, and simply helpers to copy to and from it.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  include/linux/sockptr.h | 104 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 104 insertions(+)
>  create mode 100644 include/linux/sockptr.h
>
> diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h
> new file mode 100644
> index 00000000000000..700856e13ea0c4
> --- /dev/null
> +++ b/include/linux/sockptr.h
> @@ -0,0 +1,104 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2020 Christoph Hellwig.
> + *
> + * Support for "universal" pointers that can point to either kernel or userspace
> + * memory.
> + */
> +#ifndef _LINUX_SOCKPTR_H
> +#define _LINUX_SOCKPTR_H
> +
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +typedef struct {
> +       union {
> +               void            *kernel;
> +               void __user     *user;
> +       };
> +       bool            is_kernel : 1;
> +} sockptr_t;
>

I am not sure why you chose sockptr_t   for something that really seems generic.

Or is it really meant to be exclusive to setsockopt() and/or getsockopt() ?

If the first user of this had been futex code, we would have used
futexptr_t, I guess.