utsname_sysctl.c

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/*
 *  Copyright (C) 2007
 *
 *  Author: Eric Biederman <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as
 *  published by the Free Software Foundation, version 2 of the
 *  License.
 */

#include <linux/export.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/sysctl.h>
#include <linux/wait.h>

static void *get_uts(ctl_table *table, int write)
{
    char *which = table->data;
    struct uts_namespace *uts_ns;

    uts_ns = current->nsproxy->uts_ns;
    which = (which - (char *)&init_uts_ns) + (char *)uts_ns;

    if (!write)
        down_read(&uts_sem);
    else
        down_write(&uts_sem);
    return which;
}

static void put_uts(ctl_table *table, int write, void *which)
{
    if (!write)
        up_read(&uts_sem);
    else
        up_write(&uts_sem);
}

#ifdef CONFIG_PROC_SYSCTL
/*
 *  Special case of dostring for the UTS structure. This has locks
 *  to observe. Should this be in kernel/sys.c ????
 */
static int proc_do_uts_string(ctl_table *table, int write,
          void __user *buffer, size_t *lenp, loff_t *ppos)
{
    struct ctl_table uts_table;
    int r;
    memcpy(&uts_table, table, sizeof(uts_table));
    uts_table.data = get_uts(table, write);
    r = proc_dostring(&uts_table,write,buffer,lenp, ppos);
    put_uts(table, write, uts_table.data);

    if (write)
        proc_sys_poll_notify(table->poll);

    return r;
}
#else
#define proc_do_uts_string NULL
#endif

static DEFINE_CTL_TABLE_POLL(hostname_poll);
static DEFINE_CTL_TABLE_POLL(domainname_poll);

static struct ctl_table uts_kern_table[] = {
    {
        .procname   = "ostype",
        .data       = init_uts_ns.name.sysname,
        .maxlen     = sizeof(init_uts_ns.name.sysname),
        .mode       = 0444,
        .proc_handler   = proc_do_uts_string,
    },
    {
        .procname   = "osrelease",
        .data       = init_uts_ns.name.release,
        .maxlen     = sizeof(init_uts_ns.name.release),
        .mode       = 0444,
        .proc_handler   = proc_do_uts_string,
    },
    {
        .procname   = "version",
        .data       = init_uts_ns.name.version,
        .maxlen     = sizeof(init_uts_ns.name.version),
        .mode       = 0444,
        .proc_handler   = proc_do_uts_string,
    },
    {
        .procname   = "hostname",
        .data       = init_uts_ns.name.nodename,
        .maxlen     = sizeof(init_uts_ns.name.nodename),
        .mode       = 0644,
        .proc_handler   = proc_do_uts_string,
        .poll       = &hostname_poll,
    },
    {
        .procname   = "domainname",
        .data       = init_uts_ns.name.domainname,
        .maxlen     = sizeof(init_uts_ns.name.domainname),
        .mode       = 0644,
        .proc_handler   = proc_do_uts_string,
        .poll       = &domainname_poll,
    },
    {}
};

static struct ctl_table uts_root_table[] = {
    {
        .procname   = "kernel",
        .mode       = 0555,
        .child      = uts_kern_table,
    },
    {}
};

#ifdef CONFIG_PROC_SYSCTL
/*
 * Notify userspace about a change in a certain entry of uts_kern_table,
 * identified by the parameter proc.
 */
void uts_proc_notify(enum uts_proc proc)
{
    struct ctl_table *table = &uts_kern_table[proc];

    proc_sys_poll_notify(table->poll);
}
#endif

static int __init utsname_sysctl_init(void)
{
    register_sysctl_table(uts_root_table);
    return 0;
}

__initcall(utsname_sysctl_init);