s390: simplify dynamic sysctl registration for appldata_register_ops

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 ops->name and that is     ops->ctl_table[2]. It needs an empty
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, ...).

[gor@linux.ibm.com: appldata_generic_handler fixup ctl_table index 2->0]
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20230310234525.3986352-7-mcgrof@kernel.orgReviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

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;
 		}
 	}
@@ -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;