[PATCH v5 0/2] change the proc handler for nsm_use_hostnames

From: Jia He
Date: Thu Dec 15 2016 - 02:26:33 EST

nsm_use_hostnames is a module parameter and it will be exported to sysctl
procfs. This is to let user sometimes change it from userspace. But the
minimal unit for sysctl procfs read/write it sizeof(int).
In big endian system, the converting from/to bool to/from int will cause
error for proc items.

This patch introduces a new proc handler proc_dobool for nsm_use_hostnames.

v5: Fix compilation error when CONFIG_PROC_SYSCTL is not set
v4: Change (u8 *) to (bool *)
v3: Introduce a new proc handler proc_dou8vec(suggested by Xinhui Pan)
v2: Change extern type in lockd.h

The test case I used:
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sysctl.h>

bool __read_mostly nsm_use_hostnames;
module_param(nsm_use_hostnames, bool, 0644);

static struct ctl_table my_sysctl[] = {
.procname = "nsm_use_hostnames",
.data = &nsm_use_hostnames,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec,

static struct ctl_table my_root[] = {
.procname = "mysysctl",
.mode = 0555,
.child = my_sysctl,

static struct ctl_table_header * my_ctl_header;

static int __init sysctl_exam_init(void)
my_ctl_header = register_sysctl_table(&my_root);
if (my_ctl_header == NULL)
printk("error regiester sysctl");

return 0;

static void __exit sysctl_exam_exit(void)


[root@bigendian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
[root@bigendian my]# cat /proc/sys/mysysctl/nsm_use_hostnames

After I change the proc_dointvec to new handler proc_dou8vec with the
[root@bigendian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
[root@bigendian my]# cat /proc/sys/mysysctl/nsm_use_hostnames

In little endian system, there is no such issue.
Already tested in both of big and little endian(ppc64 and ppc64le)

Jia He (2):
sysctl: introduce new proc handler proc_dobool
lockd: change the proc_handler for nsm_use_hostnames

fs/lockd/svc.c | 2 +-
include/linux/sysctl.h | 2 ++
kernel/sysctl.c | 41 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 44 insertions(+), 1 deletion(-)