linux-kernel - Re: [PATCH V8 36/44] memremap_pages: Reserve a PKS PKey for eventual use by PMEM

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Date:   Tue, 1 Feb 2022 18:35:21 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "hpa@...or.com" <hpa@...or.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V8 36/44] memremap_pages: Reserve a PKS PKey for eventual
 use by PMEM

On Thu, 2022-01-27 at 09:54 -0800, ira.weiny@...el.com wrote:
>  enum pks_pkey_consumers {
> -       PKS_KEY_DEFAULT         = 0, /* Must be 0 for default PTE
> values */
> -       PKS_KEY_TEST            = 1,
> -       PKS_KEY_NR_CONSUMERS    = 2,
> +       PKS_KEY_DEFAULT                 = 0, /* Must be 0 for default
> PTE values */
> +       PKS_KEY_TEST                    = 1,
> +       PKS_KEY_PGMAP_PROTECTION        = 2,
> +       PKS_KEY_NR_CONSUMERS            = 3,
>  };

The c spec says that any enum member that doesn't have an "=" will be
one more than the previous member. As a consequence you can leave the
"=" off PKS_KEY_NR_CONSUMERS and it will get auto adjusted when you add
more like this.

I know we've gone around and around on this, but why also specify the
value for each key? They should auto increment and the first one is
guaranteed to be zero.

Otherwise this doesn't use any of the features of "enum", it's just a
verbose series of const int's.