linux-kernel - Re: [PATCH v4 2/4] sysctl: Move some boundary constants form sysctl.c to sysctl

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Date:   Tue, 19 May 2020 13:44:30 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Xiaoming Ni <nixiaoming@...wei.com>, keescook@...omium.org
Cc:     mcgrof@...nel.org, yzaikin@...gle.com, adobriyan@...il.com,
        mingo@...nel.org, gpiccoli@...onical.com, rdna@...com,
        patrick.bellasi@....com, sfr@...b.auug.org.au,
        akpm@...ux-foundation.org, mhocko@...e.com, vbabka@...e.cz,
        tglx@...utronix.de, peterz@...radead.org,
        Jisheng.Zhang@...aptics.com, khlebnikov@...dex-team.ru,
        bigeasy@...utronix.de, pmladek@...e.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        wangle6@...wei.com, alex.huangjianhui@...wei.com
Subject: Re: [PATCH v4 2/4] sysctl: Move some boundary constants form sysctl.c
 to sysctl_vals

On 2020/05/19 12:31, Xiaoming Ni wrote:
> Some boundary (.extra1 .extra2) constants (E.g: neg_one two) in
> sysctl.c are used in multiple features. Move these variables to
> sysctl_vals to avoid adding duplicate variables when cleaning up
> sysctls table.
> 
> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>

I feel that it is use of

	void *extra1;
	void *extra2;

in "struct ctl_table" that requires constant values indirection.
Can't we get rid of sysctl_vals using some "union" like below?

struct ctl_table {
	const char *procname;           /* Text ID for /proc/sys, or zero */
	void *data;
	int maxlen;
	umode_t mode;
	struct ctl_table *child;        /* Deprecated */
	proc_handler *proc_handler;     /* Callback for text formatting */
	struct ctl_table_poll *poll;
	union {
		void *min_max_ptr[2];
		int min_max_int[2];
		long min_max_long[2];
	};
} __randomize_layout;