linux-kernel - [PATCH v5 0/2] change the proc handler for nsm_use

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Date:   Thu, 15 Dec 2016 15:24:19 +0800
From:   Jia He <hejianet@...il.com>
To:     linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Serge Hallyn <serge@...lyn.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Kees Cook <keescook@...omium.org>,
        Hugh Dickins <hughd@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Daniel Cashman <dcashman@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Jia He <hejianet@...il.com>
Subject: [PATCH v5 0/2] change the proc handler for nsm_use_hostnames

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.

Changes:
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)
{
        unregister_sysctl_table(my_ctl_header);
}

module_init(sysctl_exam_init);
module_exit(sysctl_exam_exit);
MODULE_LICENSE("GPL");
/****************************************************************/

[root@...endian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1   
[root@...endian my]# cat /proc/sys/mysysctl/nsm_use_hostnames 
16777216

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

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(-)
-- 
2.5.5