Re: [PATCH v2 0/1] lockd: Change nsm_use_hostnames from bool to u32

[Pan Xinhui]

å 2016/12/11 23:36, Jia He åé:
> 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.
hi, Jia

not only in BE system. :)
Current code is just touching a wrong pointer.

some tests based on yours

u8 __read_mostly nsm_use_hostnames[4]={1,2,3,4}; // an arrary of u8, and [0] passed to ctl_table as data

static struct ctl_table my_sysctl[] = {
        {
                .procname       = "nsm_use_hostnames",
                .data           = &nsm_use_hostnames[0],//u8,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = &proc_dointvec,
        },
        {}
};

then run your tests and result will be

root@ltcalpine2-lp13:~/linux/bench# cat /proc/sys/mysysctl/nsm_use_hostnames
67305985( This is 0x4030201, expected be 0x1)

So your fix patch work around it. But I suggest we can support u8/u16, not only int/double int.

thanks
xinhui
 
> This patch changes the type definition of nsm_use_hostnames.
>
> 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@bigendian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
> [root@bigendian my]# cat /proc/sys/mysysctl/nsm_use_hostnames
> 16777216
>
> After I change the bool to int:
> [root@bigendian my]# insmod -f /root/my/hello.ko nsm_use_hostnames=1
> [root@bigendian my]# cat /proc/sys/mysysctl/nsm_use_hostnames
> 1
>
> In little endian system, there is no such issue.
>
> Jia He (1):
>   lockd: Change nsm_use_hostnames from bool to u32
>
>  fs/lockd/mon.c              | 2 +-
>  fs/lockd/svc.c              | 2 +-
>  include/linux/lockd/lockd.h | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)