tighten up polkit-auth, implement in hostnamed.c

[systembsd.git] / src / interfaces / hostnamed / hostnamed.c

/*
 * Copyright (c) 2014 Ian Sutton <ian@kremlin.cc>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <unistd.h>
#include <limits.h>
#include <signal.h>
#include <string.h>

#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/sensors.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>

#include <machine/apmvar.h>

#include <glib/gprintf.h>
#include <glib-unix.h>
#include <polkit/polkit.h>

#include "hostnamed-gen.h"
#include "hostnamed.h"

#include "../../polkit-auth.h"

/* format: {
 *           (1) string to be matched against runtime machine's sysctl output.
 *               can be either the exact string or a substring contained
 *               within sysctl strings. no "guesses" here, a match should
 *               reliably indicate the chassis/icon. 
 *
 *           (2) string describing chassis type divulged by (1).
 *               must be one of "desktop", "laptop", "server",
 *               "tablet", "handset", "vm", "container" or NULL
 *               if only icon string can be ascertained. "vm" refers
 *               to operating systems running on baremetal hypervisors
 *               (hardware virtualization, like XEN) while "container"
 *               refers to OSs running on shared hypervisors like
 *               virtualbox or VMware. consider the distinction carefully
 *               as common virtualization software like KVM may share
 *               characteristics of both "vm" and "container" types.
 *
 *           (3) string specifying icon to use. follows XDG icon spec.
 *               see http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html
 *               for allowed strings.
 *
 *           (4) chassis precedence bit. TRUE if (2) is defined and
 *               we're certain it is the proper string. FALSE in the
 *               circumstance (2) may be the correct string, unless
 *               a match with this bit set to TRUE overrides it.
 *               if (2) is NULL, this bit is inconsequential.
 *
 *           (5) icon precedence bit. see previous definition.
 *         }                                               */
struct SYSCTL_LOOKUP_TABLE {
    gchar    *match_string;
    gchar    *chassis;
    gchar    *icon;
    gboolean chassis_precedence;
    gboolean icon_precedence;
};

GPtrArray *hostnamed_freeable;
Hostname1 *hostnamed_interf;

GMainLoop *hostnamed_loop;

guint bus_descriptor;
gboolean dbus_interface_exported; /* reliable because of gdbus operational guarantees */

gchar *HOSTNAME, *STATIC_HOSTNAME, *PRETTY_HOSTNAME;
gchar *CHASSIS, *ICON;
gchar *KERN_NAME, *KERN_RELEASE, *KERN_VERS, *OS_CPENAME;

/* TODO no specific vm or laptop icon in gnome
 * NOTE paravirtualization on xen is only available for linuxes right now
 * dmesg on linux systems reveals xen and virtualization method (HVM or PVM) 
 * but we will worry about those later */

/* add any sysctl strings that suggest virtualization here */
const struct SYSCTL_LOOKUP_TABLE chassis_indicator_table[] =
{
    { "QEMU Virtual CPU",        "vm",        NULL,              FALSE, FALSE }, /* could be QEMU running in userspace or as part of KVM */
    { "KVM",                     "vm",        "drive-multidisk", FALSE, FALSE },
    { "SmartDC HVM",             "vm",        "drive-multidisk", TRUE,  TRUE  }, /* illumos-joyent kvm */
    { "VirtualBox",              "vm",        "drive-multidisk", TRUE,  TRUE  },
    { "VMware, Inc.",            "vm",        "drive-multidisk", TRUE,  TRUE  },
    { "VMware Virtual Platform", "vm",        "drive-multidisk", TRUE,  TRUE  },
    { "Parallels",               "vm",        "drive-multidisk", TRUE,  TRUE  }, /* need verification */
    { "Xen",                     "vm",        "drive-multidisk", FALSE, FALSE } 
}; /* TODO: chroots, etc. are the actual "containers", add them */

/* archs to check against when determining if machine is server */
const gchar *server_archs[] = {
    "hppa",
    "sparc",
    "sparc64"
};

/* --- begin method/property/dbus signal code --- */

/* TODO free some strings here */
static gboolean
on_handle_set_hostname(Hostname1 *hn1_passed_interf,
                       GDBusMethodInvocation *invoc,
                       const gchar *greet,
                       gpointer data) {
    GVariant *params;
    gchar *proposed_hostname, *valid_hostname_buf;
    const gchar *bus_name;
    gboolean policykit_auth, ret, try_to_set;
    size_t check_length;
    check_auth_result is_authed;

    proposed_hostname = NULL;
    ret = try_to_set = FALSE;
    
    params = g_dbus_method_invocation_get_parameters(invoc);
    g_variant_get(params, "(sb)", &proposed_hostname, &policykit_auth);
    bus_name = g_dbus_method_invocation_get_sender(invoc);

    /* verify caller has correct permissions via polkit */
    is_authed = polkit_try_auth(bus_name, "org.freedesktop.hostname1.SetHostname", policykit_auth);

    switch(is_authed) {

        case AUTHORIZED_NATIVELY:
        case AUTHORIZED_BY_PROMPT:
            try_to_set = TRUE;
            break;

        case UNAUTHORIZED_NATIVELY:
        case UNAUTHORIZED_FAILED_PROMPT:
            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.EACCES", "Insufficient permissions to set hostname.");
            break;

        case ERROR_BADBUS:
            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.EFAULT", "Provided bus name is invalid.");
            break;

        case ERROR_BADACTION:
            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.EFAULT", "Provided action ID is invalid.");
            break;

        case ERROR_GENERIC:
        default:
            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.ECANCELED", "Failed to set hostname for unknown reason.");
            break;
    }

    /* verify passed hostname's validity */
    if(try_to_set && proposed_hostname && (valid_hostname_buf = g_hostname_to_ascii(proposed_hostname))) {

        check_length = strnlen(valid_hostname_buf, MAXHOSTNAMELEN + 1);

        if(check_length > MAXHOSTNAMELEN) {

            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.ENAMETOOLONG", "Hostname string exceeded maximum length.");
            g_free(valid_hostname_buf);

        } else if(sethostname(proposed_hostname, check_length)) {

            g_dbus_method_invocation_return_dbus_error(invoc, "org.freedesktop.hostname1.Error.ECANCELED", "Failed to set hostname for unknown reason.");
            g_free(valid_hostname_buf);

        } else {

            HOSTNAME = valid_hostname_buf;
            hostname1_set_hostname(hn1_passed_interf, HOSTNAME);
            g_ptr_array_add(hostnamed_freeable, valid_hostname_buf);
            ret = TRUE;
            hostname1_complete_set_hostname(hn1_passed_interf, invoc);
        }
    }

    return ret;
}

static gboolean
on_handle_set_static_hostname(Hostname1 *hn1_passed_interf,
                              GDBusMethodInvocation *invoc,
                              const gchar *greet,
                              gpointer data) {
    return FALSE;
}

static gboolean
on_handle_set_pretty_hostname(Hostname1 *hn1_passed_interf,
                              GDBusMethodInvocation *invoc,
                              const gchar *greet,
                              gpointer data) {
    return FALSE;
}

static gboolean
on_handle_set_chassis(Hostname1 *hn1_passed_interf,
                      GDBusMethodInvocation *invoc,
                      const gchar *greet,
                      gpointer data) {
    return FALSE;
}

static gboolean
on_handle_set_icon_name(Hostname1 *hn1_passed_interf,
                        GDBusMethodInvocation *invoc,
                        const gchar *greet,
                        gpointer data) {
    return FALSE;
}

/* note: all hostnamed/hostname1's properties are read-only,
 * and do not need set_ functions, gdbus-codegen realized
 * this from the XML and handled the to-be error of trying
 * to set a read-only property's value 
 */

const gchar *
our_get_hostname() {

    gchar *hostname_buf;
    hostname_buf = (gchar *)g_malloc0(MAXHOSTNAMELEN);

    if(gethostname(hostname_buf, MAXHOSTNAMELEN))
        return "localhost.home.network"; /* TODO bomb out here probably */
    
    else if(!g_strcmp0(HOSTNAME, hostname_buf)) {

        g_free(hostname_buf);
        return HOSTNAME;
    }

    g_ptr_array_add(hostnamed_freeable, hostname_buf);
    HOSTNAME = hostname_buf;
    hostname1_set_hostname(hostnamed_interf, HOSTNAME);

    return HOSTNAME;
}

const gchar *
our_get_static_hostname() {

    if(STATIC_HOSTNAME && g_strcmp0(STATIC_HOSTNAME, ""))
        return STATIC_HOSTNAME;
    else if(HOSTNAME)
        return HOSTNAME;

    return "localhost.home.network";
}

const gchar *
our_get_pretty_hostname() {

    if(PRETTY_HOSTNAME)
        return PRETTY_HOSTNAME;

    return "";
}

const gchar *
our_get_chassis() {

   if(CHASSIS)
        return CHASSIS;

    return "desktop"; /* this leads to the most generic beheivor in the unlikely case its returned */
}

const gchar *
our_get_icon_name() {

    if(ICON)
        return ICON;

    return "";
}

const gchar *
our_get_kernel_name() {

    if(KERN_NAME)
        return KERN_NAME;

    return "";
}

const gchar *
our_get_kernel_version() {

    if(KERN_VERS)
        return KERN_VERS;

    return "";
}

const gchar *
our_get_kernel_release() {

    if(KERN_RELEASE)
        return KERN_RELEASE;

    return "";
}

const gchar *
our_get_os_cpename() {

    return "ONEDAY";
}

const gchar *
our_get_os_pretty_name() {

    return "OpenBSD";
}

/* --- end method/property/dbus signal code, begin bus/name handlers --- */

static void hostnamed_on_bus_acquired(GDBusConnection *conn,
                                      const gchar *name,
                                      gpointer user_data) {

    g_printf("got bus/name, exporting %s's interface...\n", name);

    hostnamed_interf = hostname1_skeleton_new();

    /* attach function pointers to generated struct's method handlers */
    g_signal_connect(hostnamed_interf, "handle-set-hostname", G_CALLBACK(on_handle_set_hostname), NULL);
    g_signal_connect(hostnamed_interf, "handle-set-static-hostname", G_CALLBACK(on_handle_set_static_hostname), NULL);
    g_signal_connect(hostnamed_interf, "handle-set-pretty-hostname", G_CALLBACK(on_handle_set_pretty_hostname), NULL);
    g_signal_connect(hostnamed_interf, "handle-set-chassis", G_CALLBACK(on_handle_set_chassis), NULL);
    g_signal_connect(hostnamed_interf, "handle-set-icon-name", G_CALLBACK(on_handle_set_icon_name), NULL);

    /* set our properties before export */
    hostname1_set_hostname(hostnamed_interf, our_get_hostname());
    hostname1_set_static_hostname(hostnamed_interf, our_get_static_hostname());
    hostname1_set_pretty_hostname(hostnamed_interf, our_get_pretty_hostname());
    hostname1_set_chassis(hostnamed_interf, our_get_chassis());
    hostname1_set_icon_name(hostnamed_interf, our_get_icon_name());
    hostname1_set_kernel_name(hostnamed_interf, our_get_kernel_name());
    hostname1_set_kernel_version(hostnamed_interf, our_get_kernel_version());
    hostname1_set_kernel_release(hostnamed_interf, our_get_kernel_release());
    hostname1_set_operating_system_cpename(hostnamed_interf, our_get_os_cpename());
    hostname1_set_operating_system_pretty_name(hostnamed_interf, our_get_os_pretty_name());
 
    if(!g_dbus_interface_skeleton_export(G_DBUS_INTERFACE_SKELETON(hostnamed_interf),
                                         conn,
                                         "/org/freedesktop/hostname1",
                                         NULL)) {

        g_printf("failed to export %s's interface!\n", name); /* unusual edge case, TODO check errno */
        hostnamed_mem_clean();

    } else {

        dbus_interface_exported = TRUE;
        g_printf("exported %s's interface on the system bus...\n", name);
    }
}

static void hostnamed_on_name_acquired(GDBusConnection *conn,
                                       const gchar *name,
                                       gpointer user_data) {

    g_printf("success!\n");
}

static void hostnamed_on_name_lost(GDBusConnection *conn,
                                   const gchar *name,
                                   gpointer user_data) {

    if(!conn) {

        g_printf("failed to connect to the system bus while trying to acquire name '%s': either dbus-daemon isn't running or we don't have permission to push names and/or their interfaces to it.\n", name);
        hostnamed_mem_clean();
    }

    g_printf("lost name %s, exiting...\n", name);

    hostnamed_mem_clean();
}

/* --- end bus/name handlers, begin misc unix functions --- */

/* safe call to clean and then exit
 * this stops our GMainLoop safely before letting main() return */
void hostnamed_mem_clean() {

    g_printf("exiting...\n");

    if(dbus_interface_exported)
        g_dbus_interface_skeleton_unexport(G_DBUS_INTERFACE_SKELETON(hostnamed_interf));

    if(g_main_loop_is_running(hostnamed_loop)) 
        g_main_loop_quit(hostnamed_loop);

}

/* wrapper for glib's unix signal handling; called only once if terminatating signal is raised against us */
gboolean unix_sig_terminate_handler(gpointer data) {

    g_printf("caught SIGINT/HUP/TERM, exiting\n");

    hostnamed_mem_clean();
    return G_SOURCE_REMOVE; 
}

void set_signal_handlers() {

    /* we don't care about its descriptor, we never need to unregister these */
    g_unix_signal_add(SIGINT,  unix_sig_terminate_handler, NULL);
    g_unix_signal_add(SIGHUP,  unix_sig_terminate_handler, NULL);
    g_unix_signal_add(SIGTERM, unix_sig_terminate_handler, NULL);

    /* TODO: the "only once" guarantee only counts towards specific signals.
     *       make sure calling a SIGINT and SIGHUP doesn't cause term_handler()
     *       to be called twice */
}

int main() {
 
    hostnamed_freeable = g_ptr_array_new();
  
    /* TODO: check for valid, writable config at init. if no, complain to `make install` */

    CHASSIS = ICON = OS_CPENAME = 0;
    KERN_NAME = KERN_RELEASE = KERN_VERS = 0;
    HOSTNAME = STATIC_HOSTNAME = PRETTY_HOSTNAME = NULL;

    set_signal_handlers();

    if(!determine_chassis_and_icon() || !set_uname_properties() || !set_names())
        return 1;
    
    hostnamed_loop = g_main_loop_new(NULL, TRUE);

    bus_descriptor = g_bus_own_name(G_BUS_TYPE_SYSTEM,
                                   "org.freedesktop.hostname1",
                                   G_BUS_NAME_OWNER_FLAGS_NONE,
                                   hostnamed_on_bus_acquired,
                                   hostnamed_on_name_acquired,
                                   hostnamed_on_name_lost,
                                   NULL,
                                   NULL);

    g_main_loop_run(hostnamed_loop);
    /* runs until single g_main_loop_quit() call is raised inside <interface>_mem_clean() */
    g_main_loop_unref(hostnamed_loop);

    /* guaranteed unownable */
    g_bus_unown_name(bus_descriptor);

    /* at this point no operations can occur with our data, it is safe to free it + its container */
    g_ptr_array_free(hostnamed_freeable, TRUE);

    return 0;
}

gboolean set_names() {

    /* (1) set up */
    gchar *hostname_buf, *static_hostname_buf, *pretty_hostname_buf;
    GKeyFile *config;
    size_t hostname_divider;

    hostname_buf        = (gchar*) g_malloc0(MAXHOSTNAMELEN);
    static_hostname_buf = (gchar*) g_malloc0(4096);
    pretty_hostname_buf = (gchar*) g_malloc0(4096);

    config = g_key_file_new();

    g_ptr_array_add(hostnamed_freeable, hostname_buf);
    g_ptr_array_add(hostnamed_freeable, static_hostname_buf);
    g_ptr_array_add(hostnamed_freeable, pretty_hostname_buf);

    /* (2) set HOSTNAME */
    if(gethostname(hostname_buf, MAXHOSTNAMELEN) || !g_strcmp0(hostname_buf, "")) 
        HOSTNAME = "localhost";

    HOSTNAME = hostname_buf;

    /* this bit gets you the /etc/myname style hostname
    hostname_divider = strcspn(hostname_buf, ".");
    strncpy(ret, hostname_buf, hostname_divider); */

    /* (3) set PRETTY_HOSTNAME */
    if(g_key_file_load_from_file(config, "/etc/systemd_compat.conf", G_KEY_FILE_NONE, NULL)
        && (pretty_hostname_buf = g_key_file_get_value(config, "hostnamed", "PrettyHostname", NULL)))
        PRETTY_HOSTNAME = pretty_hostname_buf;
    else
        PRETTY_HOSTNAME = "";
 
    if(config)
        g_key_file_unref(config);

    /* (4) set STATIC_HOSTNAME */ 
    if(!g_strcmp0(PRETTY_HOSTNAME, ""))
        STATIC_HOSTNAME = HOSTNAME;

    else if((static_hostname_buf = g_hostname_to_ascii(PRETTY_HOSTNAME)))
        STATIC_HOSTNAME = static_hostname_buf;

    return (HOSTNAME && STATIC_HOSTNAME && PRETTY_HOSTNAME) ? TRUE : FALSE;

}

gboolean set_uname_properties() {

    struct utsname un;

    if(-1 == uname(&un))
        return FALSE;

    KERN_NAME = (gchar*)g_malloc0(sizeof(un.sysname));
    g_ptr_array_add(hostnamed_freeable, KERN_NAME);
    g_strlcpy(KERN_NAME, un.sysname, sizeof(un.sysname));

    KERN_RELEASE = (gchar*)g_malloc0(sizeof(un.release));
    g_ptr_array_add(hostnamed_freeable, KERN_RELEASE);
    g_strlcpy(KERN_RELEASE, un.release, sizeof(un.release));

    KERN_VERS = (gchar*)g_malloc0(sizeof(un.version));
    g_ptr_array_add(hostnamed_freeable, KERN_VERS);
    g_strlcpy(KERN_VERS, un.version, sizeof(un.version));

    return TRUE;
}

gboolean determine_chassis_and_icon() {

    const size_t bufsize = 4096;    

    char *hwproduct, *hwmodel, *hwvendor, *hwmachine;
    size_t hwproduct_size, hwmodel_size, hwvendor_size, hwmachine_size;
    int hwproduct_name[2], hwmodel_name[2], hwvendor_name[2], hwmachine_name[2];
    unsigned int i;
    gboolean UNSURE_CHASSIS_FLAG, UNSURE_ICON_FLAG;

    hwproduct_size = hwmodel_size = hwvendor_size = hwmachine_size = bufsize;
    UNSURE_CHASSIS_FLAG = UNSURE_ICON_FLAG = FALSE;
    i = 0;

    hwproduct = (char*)g_malloc0(4096);
    hwmodel   = (char*)g_malloc0(4096);
    hwvendor  = (char*)g_malloc0(4096);
    hwmachine = (char*)g_malloc0(4096);

    g_ptr_array_add(hostnamed_freeable, hwproduct);
    g_ptr_array_add(hostnamed_freeable, hwmodel);
    g_ptr_array_add(hostnamed_freeable, hwvendor);
    g_ptr_array_add(hostnamed_freeable, hwmachine);

    hwproduct_name[0] = CTL_HW;
    hwproduct_name[1] = HW_PRODUCT;

    hwmodel_name[0] = CTL_HW;
    hwmodel_name[1] = HW_MODEL;

    hwvendor_name[0] = CTL_HW;
    hwvendor_name[1] = HW_VENDOR;

    hwmachine_name[0] = CTL_HW;
    hwmachine_name[1] = HW_MACHINE;

    /* pass NULL buffer to check size first, then pass hw to be filled according to freshly-set hw_size */
    if(-1 == sysctl(hwproduct_name, 2, NULL, &hwproduct_size, NULL, 0) || -1 == sysctl(hwproduct_name, 2, hwproduct, &hwproduct_size, NULL, 0))
        return FALSE;

    if(-1 == sysctl(hwmodel_name, 2, NULL, &hwmodel_size, NULL, 0) || -1 == sysctl(hwmodel_name, 2, hwmodel, &hwmodel_size, NULL, 0))
        return FALSE;
 
    if(-1 == sysctl(hwvendor_name, 2, NULL, &hwvendor_size, NULL, 0) || -1 == sysctl(hwvendor_name, 2, hwvendor, &hwvendor_size, NULL, 0))
        return FALSE;

    if(-1 == sysctl(hwmachine_name, 2, NULL, &hwmachine_size, NULL, 0) || -1 == sysctl(hwmachine_name, 2, hwmachine, &hwmachine_size, NULL, 0))
        return FALSE;

    /* TODO: test for laptop, if not, dmidecode for desktop vs. server
     *       probably move this code to vm test func and set a global after running it early, once */
 
    for(; i < G_N_ELEMENTS(chassis_indicator_table); i++) {
        if(strcasestr(hwproduct,    chassis_indicator_table[i].match_string)
            || strcasestr(hwmodel,  chassis_indicator_table[i].match_string)
            || strcasestr(hwvendor, chassis_indicator_table[i].match_string)) {

            if(!UNSURE_CHASSIS_FLAG && chassis_indicator_table[i].chassis) {

                UNSURE_CHASSIS_FLAG = chassis_indicator_table[i].chassis_precedence;
                CHASSIS = chassis_indicator_table[i].chassis;
            }
            
            if(!UNSURE_ICON_FLAG && chassis_indicator_table[i].icon) {

                UNSURE_ICON_FLAG = chassis_indicator_table[i].icon_precedence;
                ICON = chassis_indicator_table[i].icon;
            }
        }
    }

    if(up_native_is_laptop()) {

        if(!CHASSIS)
            CHASSIS = "laptop";
        if(!ICON)
            ICON = "input-touchpad"; /* TODO pull an icon package that actually has the icons we're looking for */

    } else if(is_server(hwmachine)) {

        if(!CHASSIS)
            CHASSIS = "server";
        if(!ICON)
            ICON = "uninterruptible-power-supply";

    } else if(!CHASSIS || !ICON) {

        if(!CHASSIS)
            CHASSIS = "desktop";
        if(!ICON)
            ICON = "computer";
    }

    return (CHASSIS && ICON);
}

gboolean is_server(gchar *arch) {
    
    unsigned int i;

    for(; i < G_N_ELEMENTS(server_archs); i++)
        if(strcasestr(arch, server_archs[i]))
            return TRUE;

    return FALSE;
}

gboolean up_native_is_laptop() {

    struct apm_power_info bstate;
    struct sensordev acpiac;

    if (up_native_get_sensordev("acpiac0", &acpiac))
        return TRUE;

    if (-1 == ioctl(up_apm_get_fd(), APM_IOC_GETPOWER, &bstate))
        g_error("ioctl on apm fd failed : %s", g_strerror(errno));

    return bstate.ac_state != APM_AC_UNKNOWN;
}

int up_apm_get_fd() {

    static int apm_fd = 0;

    if(apm_fd == 0) {

        g_debug("apm_fd is not initialized yet, opening");

        /* open /dev/apm */
        if((apm_fd = open("/dev/apm", O_RDONLY)) == -1) {
            if(errno != ENXIO && errno != ENOENT)
                g_error("cannot open device file");
        }
    }

    return apm_fd;
}

gboolean up_native_get_sensordev(const char * id, struct sensordev * snsrdev) {

    int devn;
    size_t sdlen = sizeof(struct sensordev);
    int mib[] = {CTL_HW, HW_SENSORS, 0, 0 ,0};

    for (devn = 0 ; ; devn++) {
        mib[2] = devn;
        if(sysctl(mib, 3, snsrdev, &sdlen, NULL, 0) == -1) {
            if(errno == ENXIO)
                continue;
            if(errno == ENOENT)
                break;
        }

        if (!strcmp(snsrdev->xname, id))
            return TRUE;
    }

    return FALSE;
}