linux-kernel - Re: [PATCH 2/4] sysctl: move sysctl type to ctl_table

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Message-ID: <20240319154312.amfmomddvjyqh5yc@joelS2.panther.com>
Date: Tue, 19 Mar 2024 16:43:12 +0100
From: Joel Granados <j.granados@...sung.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
CC: "Eric W. Biederman" <ebiederm@...ssion.com>, Luis Chamberlain
	<mcgrof@...nel.org>, Kees Cook <keescook@...omium.org>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 2/4] sysctl: move sysctl type to ctl_table_header

On Thu, Feb 22, 2024 at 08:07:37AM +0100, Thomas Weißschuh wrote:
> As static initialization of the is not possible anymore move it into
> init_header() where all the other header fields are also initialized.
Please say what was done. Something like: "Moved the
SYSCTL_TABLE_TYPE_{DEFAULT,PERMANENTLY_EMPTY} enumerations from
ctl_table to ctl_table_header."

And the then you can mention the why: "Removing the mutable memeber from
ctl_table opens the ...."

> 
> Reduce memory consumption as there are less instances of
> ctl_table_header than ctl_table.
This is indeed true, but the main reasoning behind this is
constification. Right? If you want to leave this comment, I would
suggest you add something that talks about the amount of bytes saved.
Something like : "Reduce memory consumption by sizeof(int) for every
ctl_table entry in ctl_table_header". Or something similar.

> 
> Removing this mutable member also opens the way to constify static
> instances of ctl_table.
> 
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  fs/proc/proc_sysctl.c  | 10 ++++++----
>  include/linux/sysctl.h | 22 +++++++++++-----------
>  2 files changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 2f4d4329d83d..fde7a2f773f0 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -31,7 +31,7 @@ static const struct inode_operations proc_sys_dir_operations;
>  
>  /* Support for permanently empty directories */
>  static struct ctl_table sysctl_mount_point[] = {
> -	{.type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY }
> +	{ }
>  };
>  
>  /**
> @@ -49,11 +49,11 @@ struct ctl_table_header *register_sysctl_mount_point(const char *path)
>  EXPORT_SYMBOL(register_sysctl_mount_point);
>  
>  #define sysctl_is_perm_empty_ctl_header(hptr)		\
> -	(hptr->ctl_table[0].type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> +	(hptr->type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
>  #define sysctl_set_perm_empty_ctl_header(hptr)		\
> -	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> +	(hptr->type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
>  #define sysctl_clear_perm_empty_ctl_header(hptr)	\
> -	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_DEFAULT)
> +	(hptr->type = SYSCTL_TABLE_TYPE_DEFAULT)
>  
>  void proc_sys_poll_notify(struct ctl_table_poll *poll)
>  {
> @@ -208,6 +208,8 @@ static void init_header(struct ctl_table_header *head,
>  			node++;
>  		}
>  	}
> +	if (table == sysctl_mount_point)
> +		sysctl_set_perm_empty_ctl_header(head);
>  }
>  
>  static void erase_header(struct ctl_table_header *head)
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index ee7d33b89e9e..c87f73c06cb9 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -137,17 +137,6 @@ struct ctl_table {
>  	void *data;
>  	int maxlen;
>  	umode_t mode;
> -	/**
> -	 * enum type - Enumeration to differentiate between ctl target types
> -	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
> -	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
> -	 *                                       empty directory target to serve
> -	 *                                       as mount point.
> -	 */
> -	enum {
> -		SYSCTL_TABLE_TYPE_DEFAULT,
> -		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
> -	} type;
>  	proc_handler *proc_handler;	/* Callback for text formatting */
>  	struct ctl_table_poll *poll;
>  	void *extra1;
> @@ -188,6 +177,17 @@ struct ctl_table_header {
>  	struct ctl_dir *parent;
>  	struct ctl_node *node;
>  	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
> +	/**
> +	 * enum type - Enumeration to differentiate between ctl target types
> +	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
> +	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
> +	 *                                       empty directory target to serve
> +	 *                                       as mount point.
> +	 */
> +	enum {
> +		SYSCTL_TABLE_TYPE_DEFAULT,
> +		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY,
> +	} type;
>  };
>  
>  struct ctl_dir {
> 
> -- 
> 2.43.2
> 

-- 

Joel Granados

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