linux-kernel - Re: [PATCH 6/6] s390: simplify dynamic sysctl registration for appldata_register

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Date:   Mon, 13 Mar 2023 14:13:09 +0100
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     hca@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        linux-s390@...r.kernel.org, sudipm.mukherjee@...il.com,
        ebiederm@...ssion.com, keescook@...omium.org, yzaikin@...gle.com,
        j.granados@...sung.com, patches@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] s390: simplify dynamic sysctl registration for
 appldata_register_ops

On Fri, Mar 10, 2023 at 03:45:25PM -0800, Luis Chamberlain wrote:
> The routine appldata_register_ops() allocates a sysctl table
> with 4 entries. The firsts one,   ops->ctl_table[0] is the parent directory
> with an empty entry following it, ops->ctl_table[1]. The next entry is
> for the the ops->name and that is ops->ctl_table[2]. It needs an empty

for the ops->name

> entry following that, and that is ops->ctl_table[3]. And so hence the
> kcalloc(4, sizeof(struct ctl_table), GFP_KERNEL).
> 
> We can simplify this considerably since sysctl_register("foo", table)
> can create the parent directory for us if it does not exist. So we
> can just remove the first two entries and move back the ops->name to
> the first entry, and just use kcalloc(2, ...).
> 
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> ---
>  arch/s390/appldata/appldata_base.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/s390/appldata/appldata_base.c b/arch/s390/appldata/appldata_base.c
> index c593f2228083..a60c1e093039 100644
> --- a/arch/s390/appldata/appldata_base.c
> +++ b/arch/s390/appldata/appldata_base.c
> @@ -351,7 +351,8 @@ int appldata_register_ops(struct appldata_ops *ops)
>  	if (ops->size > APPLDATA_MAX_REC_SIZE)
>  		return -EINVAL;
>  
> -	ops->ctl_table = kcalloc(4, sizeof(struct ctl_table), GFP_KERNEL);
> +	/* The last entry must be an empty one */
> +	ops->ctl_table = kcalloc(2, sizeof(struct ctl_table), GFP_KERNEL);
>  	if (!ops->ctl_table)
>  		return -ENOMEM;
>  
> @@ -359,17 +360,12 @@ int appldata_register_ops(struct appldata_ops *ops)
>  	list_add(&ops->list, &appldata_ops_list);
>  	mutex_unlock(&appldata_ops_mutex);
>  
> -	ops->ctl_table[0].procname = appldata_proc_name;
> -	ops->ctl_table[0].maxlen   = 0;
> -	ops->ctl_table[0].mode     = S_IRUGO | S_IXUGO;
> -	ops->ctl_table[0].child    = &ops->ctl_table[2];
> +	ops->ctl_table[0].procname = ops->name;
> +	ops->ctl_table[0].mode     = S_IRUGO | S_IWUSR;
> +	ops->ctl_table[0].proc_handler = appldata_generic_handler;
> +	ops->ctl_table[0].data = ops;
>  
> -	ops->ctl_table[2].procname = ops->name;
> -	ops->ctl_table[2].mode     = S_IRUGO | S_IWUSR;
> -	ops->ctl_table[2].proc_handler = appldata_generic_handler;
> -	ops->ctl_table[2].data = ops;
> -
> -	ops->sysctl_header = register_sysctl_table(ops->ctl_table);
> +	ops->sysctl_header = register_sysctl(appldata_proc_name, ops->ctl_table);
>  	if (!ops->sysctl_header)
>  		goto out;
>  	return 0;
> -- 
> 2.39.1

I'll take it with the commit message change mentioned above and the following fixup,
which addresses the obvious problem found during testing:
---
diff --git a/arch/s390/appldata/appldata_base.c b/arch/s390/appldata/appldata_base.c
index a60c1e093039..f462d60679d7 100644
--- a/arch/s390/appldata/appldata_base.c
+++ b/arch/s390/appldata/appldata_base.c
@@ -281,7 +281,7 @@ appldata_generic_handler(struct ctl_table *ctl, int write,
        mutex_lock(&appldata_ops_mutex);
        list_for_each(lh, &appldata_ops_list) {
                tmp_ops = list_entry(lh, struct appldata_ops, list);
-               if (&tmp_ops->ctl_table[2] == ctl) {
+               if (&tmp_ops->ctl_table[0] == ctl) {
                        found = 1;
                }
        }
--