Subject: Re: [PATCH 11/11] sysctl: treewide: constify the ctl_table argument of handlers

From: Dave Chinner <[email-masked]>
Date: Sat, 16 Mar 2024 13:52:48 +1100

On Fri, Mar 15, 2024 at 09:48:09PM +0100, Thomas Weißschuh wrote:
> Adapt the proc_hander function signature to make it clear that handlers
> are not supposed to modify their ctl_table argument.
> 
> This is a prerequisite to moving the static ctl_table structs into
> .rodata.
> By migrating all handlers at once a lengthy transition can be avoided.
> 
> The patch was mostly generated by coccinelle with the following script:
> 
>     @@
>     identifier func, ctl, write, buffer, lenp, ppos;
>     @@
> 
>     int func(
>     - struct ctl_table *ctl,
>     + const struct ctl_table *ctl,
>       int write, void *buffer, size_t *lenp, loff_t *ppos)
>     { ... }

Which seems to have screwed up the formatting of the XFS code...

> diff --git a/fs/xfs/xfs_sysctl.c b/fs/xfs/xfs_sysctl.c
> index a191f6560f98..a3ca192eca79 100644
> --- a/fs/xfs/xfs_sysctl.c
> +++ b/fs/xfs/xfs_sysctl.c
> @@ -10,12 +10,11 @@ static struct ctl_table_header *xfs_table_header;
>  
>  #ifdef CONFIG_PROC_FS
>  STATIC int
> -xfs_stats_clear_proc_handler(
> -	struct ctl_table	*ctl,
> -	int			write,
> -	void			*buffer,
> -	size_t			*lenp,
> -	loff_t			*ppos)
> +xfs_stats_clear_proc_handler(const struct ctl_table *ctl,
> +			     int			write,
> +			     void			*buffer,
> +			     size_t			*lenp,
> +			     loff_t			*ppos)

... because this doesn't match any format I've ever seen in the
kernel. The diff for this change shold be just:

@@ -10,7 +10,7 @@ static struct ctl_table_header *xfs_table_header;
 #ifdef CONFIG_PROC_FS
 STATIC int
 xfs_stats_clear_proc_handler(
-	struct ctl_table	*ctl,
+	const struct ctl_table	*ctl,
 	int			write,
 	void			*buffer,
 	size_t			*lenp,

>  {
>  	int		ret, *valp = ctl->data;
>  
> @@ -30,12 +29,11 @@ xfs_stats_clear_proc_handler(
>  }
>  
>  STATIC int
> -xfs_panic_mask_proc_handler(
> -	struct ctl_table	*ctl,
> -	int			write,
> -	void			*buffer,
> -	size_t			*lenp,
> -	loff_t			*ppos)
> +xfs_panic_mask_proc_handler(const struct ctl_table *ctl,
> +			    int			write,
> +			    void			*buffer,
> +			    size_t			*lenp,
> +			    loff_t			*ppos)
>  {
>  	int		ret, *valp = ctl->data;
>  
> @@ -51,12 +49,11 @@ xfs_panic_mask_proc_handler(
>  #endif /* CONFIG_PROC_FS */
>  
>  STATIC int
> -xfs_deprecated_dointvec_minmax(
> -	struct ctl_table	*ctl,
> -	int			write,
> -	void			*buffer,
> -	size_t			*lenp,
> -	loff_t			*ppos)
> +xfs_deprecated_dointvec_minmax(const struct ctl_table *ctl,
> +			       int			write,
> +			       void			*buffer,
> +			       size_t			*lenp,
> +			       loff_t			*ppos)
>  {
>  	if (write) {
>  		printk_ratelimited(KERN_WARNING

And these need fixing as well.

A further quick glance at the patch reveals that there are other
similar screwed up conversions as well.

> diff --git a/kernel/delayacct.c b/kernel/delayacct.c
> index 6f0c358e73d8..513791ef573d 100644
> --- a/kernel/delayacct.c
> +++ b/kernel/delayacct.c
> @@ -44,8 +44,9 @@ void delayacct_init(void)
>  }
>  
>  #ifdef CONFIG_PROC_SYSCTL
> -static int sysctl_delayacct(struct ctl_table *table, int write, void *buffer,
> -		     size_t *lenp, loff_t *ppos)
> +static int sysctl_delayacct(const struct ctl_table *table, int write,
> +			    void *buffer,
> +			    size_t *lenp, loff_t *ppos)
>  {
>  	int state = delayacct_on;
>  	struct ctl_table t;

Like this.

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 724e6d7e128f..e2955e0d9f44 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -450,7 +450,8 @@ static void update_perf_cpu_limits(void)
>  
>  static bool perf_rotate_context(struct perf_cpu_pmu_context *cpc);
>  
> -int perf_event_max_sample_rate_handler(struct ctl_table *table, int write,
> +int perf_event_max_sample_rate_handler(const struct ctl_table *table,
> +				       int write,
>  				       void *buffer, size_t *lenp, loff_t *ppos)
>  {
>  	int ret;

And this.

> @@ -474,8 +475,10 @@ int perf_event_max_sample_rate_handler(struct ctl_table *table, int write,
>  
>  int sysctl_perf_cpu_time_max_percent __read_mostly = DEFAULT_CPU_TIME_MAX_PERCENT;
>  
> -int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
> -		void *buffer, size_t *lenp, loff_t *ppos)
> +int perf_cpu_time_max_percent_handler(const struct ctl_table *table,
> +				      int write,
> +				      void *buffer, size_t *lenp,
> +				      loff_t *ppos)
>  {
>  	int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>  

And this.

> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index b2fc2727d654..003f0f5cb111 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -239,9 +239,10 @@ static long hung_timeout_jiffies(unsigned long last_checked,
>  /*
>   * Process updating of timeout sysctl
>   */
> -static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
> -				  void *buffer,
> -				  size_t *lenp, loff_t *ppos)
> +static int proc_dohung_task_timeout_secs(const struct ctl_table *table,
> +					 int write,
> +					 void *buffer,
> +					 size_t *lenp, loff_t *ppos)
>  {
>  	int ret;
>  

And this.

> diff --git a/kernel/latencytop.c b/kernel/latencytop.c
> index 781249098cb6..0a5c22b19821 100644
> --- a/kernel/latencytop.c
> +++ b/kernel/latencytop.c
> @@ -65,8 +65,9 @@ static struct latency_record latency_record[MAXLR];
>  int latencytop_enabled;
>  
>  #ifdef CONFIG_SYSCTL
> -static int sysctl_latencytop(struct ctl_table *table, int write, void *buffer,
> -		size_t *lenp, loff_t *ppos)
> +static int sysctl_latencytop(const struct ctl_table *table, int write,
> +			     void *buffer,
> +			     size_t *lenp, loff_t *ppos)
>  {
>  	int err;
>  

And this.

I could go on, but there are so many examples of this in the patch
that I think that it needs to be toosed away and regenerated in a
way that doesn't trash the existing function parameter formatting.

-Dave.
-- 
Dave Chinner
[email-masked]