libsystemd/sd-device/sd-device.c

	sd-device.c revision 8927b1dad2d4a7330174cb924090b4635a2547fb
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen/***
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  This file is part of systemd.
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  Copyright 2008-2012 Kay Sievers <kay@vrfy.org>
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  Copyright 2014 Tom Gundersen <teg@jklm.no>
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  systemd is free software; you can redistribute it and/or modify it
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  under the terms of the GNU Lesser General Public License as published by
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  the Free Software Foundation; either version 2.1 of the License, or
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  (at your option) any later version.
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  systemd is distributed in the hope that it will be useful, but
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  WITHOUT ANY WARRANTY; without even the implied warranty of
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  Lesser General Public License for more details.
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  You should have received a copy of the GNU Lesser General Public License
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen  along with systemd; If not, see <http://www.gnu.org/licenses/>.
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen***/
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include <ctype.h>
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include <sys/types.h>
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include <net/if.h>
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include "util.h"
0617ffabe86a6d366252477eafbe59a888b149d4Tom Gundersen#include "macro.h"
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include "path-util.h"
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include "strxcpyx.h"
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include "fileio.h"
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen#include "hashmap.h"
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen#include "set.h"
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen#include "strv.h"
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
02b59d57e0c08231645120077f651151f5bb2babTom Gundersen#include "sd-device.h"
7c99d940c11e4da1863a218b6b70dd16e65b7518Tom Gundersen
7c99d940c11e4da1863a218b6b70dd16e65b7518Tom Gundersen#include "device-util.h"
7c99d940c11e4da1863a218b6b70dd16e65b7518Tom Gundersen#include "device-private.h"
7c99d940c11e4da1863a218b6b70dd16e65b7518Tom Gundersen#include "device-internal.h"
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen
7c99d940c11e4da1863a218b6b70dd16e65b7518Tom Gundersenint device_new_aux(sd_device **ret) {
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen        _cleanup_device_unref_ sd_device *device = NULL;
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        assert(ret);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        device = new0(sd_device, 1);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        if (!device)
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                return -ENOMEM;
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        device->n_ref = 1;
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen        device->watch_handle = -1;
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        *ret = device;
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        device = NULL;
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        return 0;
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen}
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen_public_ sd_device *sd_device_ref(sd_device *device) {
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen        if (device)
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                assert_se(++ device->n_ref >= 2);
02b59d57e0c08231645120077f651151f5bb2babTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        return device;
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen}
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen_public_ sd_device *sd_device_unref(sd_device *device) {
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen        if (device && -- device->n_ref == 0) {
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen                sd_device_unref(device->parent);
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen                free(device->syspath);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                free(device->sysname);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                free(device->devtype);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                free(device->devname);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                free(device->subsystem);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                free(device->driver);
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen                free(device->id_filename);
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen                free(device->properties_strv);
12e0f830f592ec4c6bb49ac7ae1e0e84f74105e3Tom Gundersen                free(device->properties_nulstr);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                ordered_hashmap_free_free_free(device->properties);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                ordered_hashmap_free_free_free(device->properties_db);
f579559b3a14c1f1ef96c372e7626c4733e6ef7dTom Gundersen                hashmap_free_free_free(device->sysattr_values);
                set_free_free(device->sysattrs);
                set_free_free(device->tags);
                set_free_free(device->devlinks);

                free(device);
        }

        return NULL;
}

int device_add_property_aux(sd_device *device, const char *_key, const char *_value, bool db) {
        OrderedHashmap **properties;

        assert(device);
        assert(_key);

        if (db)
                properties = &device->properties_db;
        else
                properties = &device->properties;

        if (_value) {
                _cleanup_free_ char *key = NULL, *value = NULL, *old_key = NULL, *old_value = NULL;
                int r;

                r = ordered_hashmap_ensure_allocated(properties, &string_hash_ops);
                if (r < 0)
                        return r;

                key = strdup(_key);
                if (!key)
                        return -ENOMEM;

                value = strdup(_value);
                if (!value)
                        return -ENOMEM;

                old_value = ordered_hashmap_get2(*properties, key, (void**) &old_key);

                r = ordered_hashmap_replace(*properties, key, value);
                if (r < 0)
                        return r;

                key = NULL;
                value = NULL;
        } else {
                _cleanup_free_ char *key = NULL;
                _cleanup_free_ char *value = NULL;

                value = ordered_hashmap_remove2(*properties, _key, (void**) &key);
        }

        if (!db) {
                device->properties_generation ++;
                device->properties_buf_outdated = true;
        }

        return 0;
}

int device_add_property_internal(sd_device *device, const char *key, const char *value) {
        return device_add_property_aux(device, key, value, false);
}

int device_set_syspath(sd_device *device, const char *_syspath, bool verify) {
        _cleanup_free_ char *syspath = NULL;
        const char *devpath;
        int r;

        assert(device);
        assert(_syspath);

        /* must be a subdirectory of /sys */
        if (!path_startswith(_syspath, "/sys/")) {
                log_debug("sd-device: syspath '%s' is not a subdirectory of /sys", _syspath);
                return -EINVAL;
        }

        if (verify) {
                r = readlink_and_canonicalize(_syspath, &syspath);
                if (r == -ENOENT)
                        /* the device does not exist (any more?) */
                        return -ENODEV;
                else if (r == -EINVAL) {
                        /* not a symlink */
                        syspath = canonicalize_file_name(_syspath);
                        if (!syspath) {
                                if (errno == ENOENT)
                                        /* the device does not exist (any more?) */
                                        return -ENODEV;

                                log_debug("sd-device: could not canonicalize '%s': %m", _syspath);
                                return -errno;
                        }
                } else if (r < 0) {
                        log_debug("sd-device: could not get target of '%s': %s", _syspath, strerror(-r));
                        return r;
                }

                if (path_startswith(syspath,  "/sys/devices/")) {
                        char *path;

                        /* all 'devices' require an 'uevent' file */
                        path = strjoina(syspath, "/uevent");
                        r = access(path, F_OK);
                        if (r < 0) {
                                if (errno == ENOENT)
                                        /* this is not a valid device */
                                        return -ENODEV;

                                log_debug("sd-device: %s does not have an uevent file: %m", syspath);
                                return -errno;
                        }
                } else {
                        /* everything else just just needs to be a directory */
                        if (!is_dir(syspath, false))
                                return -ENODEV;
                }
        } else {
                syspath = strdup(_syspath);
                if (!syspath)
                        return -ENOMEM;
        }

        devpath = syspath + strlen("/sys");

        r = device_add_property_internal(device, "DEVPATH", devpath);
        if (r < 0)
                return r;

        free(device->syspath);
        device->syspath = syspath;
        syspath = NULL;

        device->devpath = devpath;

        return 0;
}

_public_ int sd_device_new_from_syspath(sd_device **ret, const char *syspath) {
        _cleanup_device_unref_ sd_device *device = NULL;
        int r;

        assert_return(ret, -EINVAL);
        assert_return(syspath, -EINVAL);

        r = device_new_aux(&device);
        if (r < 0)
                return r;

        r = device_set_syspath(device, syspath, true);
        if (r < 0)
                return r;

        *ret = device;
        device = NULL;

        return 0;
}

_public_ int sd_device_new_from_devnum(sd_device **ret, char type, dev_t devnum) {
        char *syspath;
        char id[DECIMAL_STR_MAX(unsigned) * 2 + 1];

        assert_return(ret, -EINVAL);
        assert_return(type == 'b' || type == 'c', -EINVAL);

        /* use /sys/dev/{block,char}/<maj>:<min> link */
        snprintf(id, sizeof(id), "%u:%u", major(devnum), minor(devnum));

        syspath = strjoina("/sys/dev/", (type == 'b' ? "block" : "char"), "/", id);

        return sd_device_new_from_syspath(ret, syspath);
}

_public_ int sd_device_new_from_subsystem_sysname(sd_device **ret, const char *subsystem, const char *sysname) {
        char *syspath;

        assert_return(ret, -EINVAL);
        assert_return(subsystem, -EINVAL);
        assert_return(sysname, -EINVAL);

        if (streq(subsystem, "subsystem")) {
                syspath = strjoina("/sys/subsystem/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);

                syspath = strjoina("/sys/bus/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);

                syspath = strjoina("/sys/class/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);
        } else  if (streq(subsystem, "module")) {
                syspath = strjoina("/sys/module/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);
        } else if (streq(subsystem, "drivers")) {
                char subsys[PATH_MAX];
                char *driver;

                strscpy(subsys, sizeof(subsys), sysname);
                driver = strchr(subsys, ':');
                if (driver) {
                        driver[0] = '\0';
                        driver++;

                        syspath = strjoina("/sys/subsystem/", subsys, "/drivers/", driver);
                        if (access(syspath, F_OK) >= 0)
                                return sd_device_new_from_syspath(ret, syspath);

                        syspath = strjoina("/sys/bus/", subsys, "/drivers/", driver);
                        if (access(syspath, F_OK) >= 0)
                                return sd_device_new_from_syspath(ret, syspath);
                } else
                        return -EINVAL;
        } else {
                syspath = strjoina("/sys/subsystem/", subsystem, "/devices/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);

                syspath = strjoina("/sys/bus/", subsystem, "/devices/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);

                syspath = strjoina("/sys/class/", subsystem, "/", sysname);
                if (access(syspath, F_OK) >= 0)
                        return sd_device_new_from_syspath(ret, syspath);
        }

        return -ENODEV;
}

int device_set_devtype(sd_device *device, const char *_devtype) {
        _cleanup_free_ char *devtype = NULL;
        int r;

        assert(device);
        assert(_devtype);

        devtype = strdup(_devtype);
        if (!devtype)
                return -ENOMEM;

        r = device_add_property_internal(device, "DEVTYPE", devtype);
        if (r < 0)
                return r;

        free(device->devtype);
        device->devtype = devtype;
        devtype = NULL;

        return 0;
}

int device_set_ifindex(sd_device *device, const char *_ifindex) {
        int ifindex, r;

        assert(device);
        assert(_ifindex);

        r = safe_atoi(_ifindex, &ifindex);
        if (r < 0)
                return r;

        if (ifindex <= 0)
                return -EINVAL;

        r = device_add_property_internal(device, "IFINDEX", _ifindex);
        if (r < 0)
                return r;

        device->ifindex = ifindex;

        return 0;
}

int device_set_devname(sd_device *device, const char *_devname) {
        _cleanup_free_ char *devname = NULL;
        int r;

        assert(device);
        assert(_devname);

        if (_devname[0] != '/') {
                r = asprintf(&devname, "/dev/%s", _devname);
                if (r < 0)
                        return -ENOMEM;
        } else {
                devname = strdup(_devname);
                if (!devname)
                        return -ENOMEM;
        }

        r = device_add_property_internal(device, "DEVNAME", devname);
        if (r < 0)
                return r;

        free(device->devname);
        device->devname = devname;
        devname = NULL;

        return 0;
}

int device_set_devmode(sd_device *device, const char *_devmode) {
        unsigned devmode;
        int r;

        assert(device);
        assert(_devmode);

        r = safe_atou(_devmode, &devmode);
        if (r < 0)
                return r;

        if (devmode > 07777)
                return -EINVAL;

        r = device_add_property_internal(device, "DEVMODE", _devmode);
        if (r < 0)
                return r;

        device->devmode = devmode;

        return 0;
}

int device_set_devnum(sd_device *device, const char *major, const char *minor) {
        unsigned maj = 0, min = 0;
        int r;

        assert(device);
        assert(major);

        r = safe_atou(major, &maj);
        if (r < 0)
                return r;
        if (!maj)
                return 0;

        if (minor) {
                r = safe_atou(minor, &min);
                if (r < 0)
                        return r;
        }

        r = device_add_property_internal(device, "MAJOR", major);
        if (r < 0)
                return r;

        if (minor) {
                r = device_add_property_internal(device, "MINOR", minor);
                if (r < 0)
                        return r;
        }

        device->devnum = makedev(maj, min);

        return 0;
}

static int handle_uevent_line(sd_device *device, const char *key, const char *value, const char **major, const char **minor) {
        int r;

        assert(device);
        assert(key);
        assert(value);
        assert(major);
        assert(minor);

        if (streq(key, "DEVTYPE")) {
                r = device_set_devtype(device, value);
                if (r < 0)
                        return r;
        } else if (streq(key, "IFINDEX")) {
                r = device_set_ifindex(device, value);
                if (r < 0)
                        return r;
        } else if (streq(key, "DEVNAME")) {
                r = device_set_devname(device, value);
                if (r < 0)
                        return r;
        } else if (streq(key, "DEVMODE")) {
                r = device_set_devmode(device, value);
                if (r < 0)
                        return r;
        } else if (streq(key, "MAJOR"))
                *major = value;
        else if (streq(key, "MINOR"))
                *minor = value;
        else {
                r = device_add_property_internal(device, key, value);
                if (r < 0)
                        return r;
        }

        return 0;
}

int device_read_uevent_file(sd_device *device) {
        _cleanup_free_ char *uevent = NULL;
        const char *syspath, *key, *value, *major = NULL, *minor = NULL;
        char *path;
        size_t uevent_len;
        unsigned i;
        int r;

        enum {
                PRE_KEY,
                KEY,
                PRE_VALUE,
                VALUE,
                INVALID_LINE,
        } state = PRE_KEY;

        assert(device);

        if (device->uevent_loaded || device->sealed)
                return 0;

        device->uevent_loaded = true;

        r = sd_device_get_syspath(device, &syspath);
        if (r < 0)
                return r;

        path = strjoina(syspath, "/uevent");

        r = read_full_file(path, &uevent, &uevent_len);
        if (r == -EACCES)
                /* empty uevent files may be write-only */
                return 0;
        else if (r == -ENOENT)
                /* some devices may not have uevent files, see set_syspath() */
                return 0;
        else if (r < 0) {
                log_debug("sd-device: failed to read uevent file '%s': %s", path, strerror(-r));
                return r;
        }

        for (i = 0; i < uevent_len; i++) {
                switch (state) {
                case PRE_KEY:
                        if (!strchr(NEWLINE, uevent[i])) {
                                key = &uevent[i];

                                state = KEY;
                        }

                        break;
                case KEY:
                        if (uevent[i] == '=') {
                                uevent[i] = '\0';

                                state = PRE_VALUE;
                        } else if (strchr(NEWLINE, uevent[i])) {
                                uevent[i] = '\0';
                                log_debug("sd-device: ignoring invalid uevent line '%s'", key);

                                state = PRE_KEY;
                        }

                        break;
                case PRE_VALUE:
                        value = &uevent[i];

                        state = VALUE;

                        break;
                case VALUE:
                        if (strchr(NEWLINE, uevent[i])) {
                                uevent[i] = '\0';

                                r = handle_uevent_line(device, key, value, &major, &minor);
                                if (r < 0)
                                        log_debug("sd-device: failed to handle uevent entry '%s=%s': %s", key, value, strerror(-r));

                                state = PRE_KEY;
                        }

                        break;
                default:
                        assert_not_reached("invalid state when parsing uevent file");
                }
        }

        if (major) {
                r = device_set_devnum(device, major, minor);
                if (r < 0)
                        log_debug("sd-device: could not set 'MAJOR=%s' or 'MINOR=%s' from '%s': %s", major, minor, path, strerror(-r));
        }

        return 0;
}

_public_ int sd_device_get_ifindex(sd_device *device, int *ifindex) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(ifindex, -EINVAL);

        r = device_read_uevent_file(device);
        if (r < 0)
                return r;

        *ifindex = device->ifindex;

        return 0;
}

_public_ int sd_device_new_from_device_id(sd_device **ret, const char *id) {
        int r;

        assert_return(ret, -EINVAL);
        assert_return(id, -EINVAL);

        switch (id[0]) {
        case 'b':
        case 'c':
        {
                char type;
                int maj, min;

                r = sscanf(id, "%c%i:%i", &type, &maj, &min);
                if (r != 3)
                        return -EINVAL;

                return sd_device_new_from_devnum(ret, type, makedev(maj, min));
        }
        case 'n':
        {
                _cleanup_device_unref_ sd_device *device = NULL;
                _cleanup_close_ int sk = -1;
                struct ifreq ifr = {};
                int ifindex;

                r = safe_atoi(&id[1], &ifr.ifr_ifindex);
                if (r < 0)
                        return r;
                else if (ifr.ifr_ifindex <= 0)
                        return -EINVAL;

                sk = socket(PF_INET, SOCK_DGRAM, 0);
                if (sk < 0)
                        return -errno;

                r = ioctl(sk, SIOCGIFNAME, &ifr);
                if (r < 0)
                        return -errno;

                r = sd_device_new_from_subsystem_sysname(&device, "net", ifr.ifr_name);
                if (r < 0)
                        return r;

                r = sd_device_get_ifindex(device, &ifindex);
                if (r < 0)
                        return r;

                /* this is racey, so we might end up with the wrong device */
                if (ifr.ifr_ifindex != ifindex)
                        return -ENODEV;

                *ret = device;
                device = NULL;

                return 0;
        }
        case '+':
        {
                char subsys[PATH_MAX];
                char *sysname;

                (void)strscpy(subsys, sizeof(subsys), id + 1);
                sysname = strchr(subsys, ':');
                if (!sysname)
                        return -EINVAL;

                sysname[0] = '\0';
                sysname ++;

                return sd_device_new_from_subsystem_sysname(ret, subsys, sysname);
        }
        default:
                return -EINVAL;
        }
}

_public_ int sd_device_get_syspath(sd_device *device, const char **ret) {
        assert_return(device, -EINVAL);
        assert_return(ret, -EINVAL);

        assert(path_startswith(device->syspath, "/sys/"));

        *ret = device->syspath;

        return 0;
}

static int device_new_from_child(sd_device **ret, sd_device *child) {
        _cleanup_free_ char *path = NULL;
        const char *subdir, *syspath;
        int r;

        assert(ret);
        assert(child);

        r = sd_device_get_syspath(child, &syspath);
        if (r < 0)
                return r;

        path = strdup(syspath);
        if (!path)
                return -ENOMEM;
        subdir = path + strlen("/sys");

        for (;;) {
                char *pos;

                pos = strrchr(subdir, '/');
                if (!pos || pos < subdir + 2)
                        break;

                *pos = '\0';

                r = sd_device_new_from_syspath(ret, path);
                if (r < 0)
                        continue;

                return 0;
        }

        return -ENODEV;
}

_public_ int sd_device_get_parent(sd_device *child, sd_device **ret) {

        assert_return(ret, -EINVAL);
        assert_return(child, -EINVAL);

        if (!child->parent_set) {
                child->parent_set = true;

                (void)device_new_from_child(&child->parent, child);
        }

        if (!child->parent)
                return -ENOENT;

        *ret = child->parent;

        return 0;
}

int device_set_subsystem(sd_device *device, const char *_subsystem) {
        _cleanup_free_ char *subsystem = NULL;
        int r;

        assert(device);
        assert(_subsystem);

        subsystem = strdup(_subsystem);
        if (!subsystem)
                return -ENOMEM;

        r = device_add_property_internal(device, "SUBSYSTEM", subsystem);
        if (r < 0)
                return r;

        free(device->subsystem);
        device->subsystem = subsystem;
        subsystem = NULL;

        device->subsystem_set = true;

        return 0;
}

_public_ int sd_device_get_subsystem(sd_device *device, const char **ret) {
        assert_return(ret, -EINVAL);
        assert_return(device, -EINVAL);

        if (!device->subsystem_set) {
                _cleanup_free_ char *subsystem = NULL;
                const char *syspath;
                char *path;
                int r;

                /* read 'subsystem' link */
                r = sd_device_get_syspath(device, &syspath);
                if (r < 0)
                        return r;

                path = strjoina(syspath, "/subsystem");
                r = readlink_value(path, &subsystem);
                if (r >= 0)
                        r = device_set_subsystem(device, subsystem);
                /* use implicit names */
                else if (path_startswith(device->devpath, "/module/"))
                        r = device_set_subsystem(device, "module");
                else if (strstr(device->devpath, "/drivers/"))
                        r = device_set_subsystem(device, "drivers");
                else if (path_startswith(device->devpath, "/subsystem/") ||
                         path_startswith(device->devpath, "/class/") ||
                         path_startswith(device->devpath, "/bus/"))
                        r = device_set_subsystem(device, "subsystem");
                if (r < 0 && r != -ENOENT)
                        return log_debug_errno(r, "sd-device: could not set subsystem for %s: %m", device->devpath);

                device->subsystem_set = true;
        }

        *ret = device->subsystem;

        return 0;
}

_public_ int sd_device_get_devtype(sd_device *device, const char **devtype) {
        int r;

        assert(devtype);
        assert(device);

        r = device_read_uevent_file(device);
        if (r < 0)
                return r;

        *devtype = device->devtype;

        return 0;
}

_public_ int sd_device_get_parent_with_subsystem_devtype(sd_device *child, const char *subsystem, const char *devtype, sd_device **ret) {
        sd_device *parent = NULL;
        int r;

        assert_return(child, -EINVAL);
        assert_return(subsystem, -EINVAL);

        r = sd_device_get_parent(child, &parent);
        while (r >= 0) {
                const char *parent_subsystem = NULL;
                const char *parent_devtype = NULL;

                (void)sd_device_get_subsystem(parent, &parent_subsystem);
                if (streq_ptr(parent_subsystem, subsystem)) {
                        if (!devtype)
                                break;

                        (void)sd_device_get_devtype(parent, &parent_devtype);
                        if (streq_ptr(parent_devtype, devtype))
                                break;
                }
                r = sd_device_get_parent(parent, &parent);
        }

        if (r < 0)
                return r;

        *ret = parent;

        return 0;
}

_public_ int sd_device_get_devnum(sd_device *device, dev_t *devnum) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(devnum, -EINVAL);

        r = device_read_uevent_file(device);
        if (r < 0)
                return r;

        *devnum = device->devnum;

        return 0;
}

int device_set_driver(sd_device *device, const char *_driver) {
        _cleanup_free_ char *driver = NULL;
        int r;

        assert(device);
        assert(_driver);

        driver = strdup(_driver);
        if (!driver)
                return -ENOMEM;

        r = device_add_property_internal(device, "DRIVER", driver);
        if (r < 0)
                return r;

        free(device->driver);
        device->driver = driver;
        driver = NULL;

        device->driver_set = true;

        return 0;
}

_public_ int sd_device_get_driver(sd_device *device, const char **ret) {
        assert_return(device, -EINVAL);
        assert_return(ret, -EINVAL);

        if (!device->driver_set) {
                _cleanup_free_ char *driver = NULL;
                const char *syspath;
                char *path;
                int r;

                r = sd_device_get_syspath(device, &syspath);
                if (r < 0)
                        return r;

                path = strjoina(syspath, "/driver");
                r = readlink_value(path, &driver);
                if (r >= 0) {
                        r = device_set_driver(device, driver);
                        if (r < 0)
                                return log_debug_errno(r, "sd-device: could not set driver for %s: %m", device->devpath);
                } else if (r == -ENOENT)
                        device->driver_set = true;
                else
                        return log_debug_errno(r, "sd-device: could not set driver for %s: %m", device->devpath);
        }

        *ret = device->driver;

        return 0;
}

_public_ int sd_device_get_devpath(sd_device *device, const char **devpath) {
        assert_return(device, -EINVAL);
        assert_return(devpath, -EINVAL);

        assert(device->devpath);
        assert(device->devpath[0] == '/');

        *devpath = device->devpath;

        return 0;
}

_public_ int sd_device_get_devname(sd_device *device, const char **devname) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(devname, -EINVAL);

        r = device_read_uevent_file(device);
        if (r < 0)
                return r;

        if (!device->devname)
                return -ENOENT;

        assert(path_startswith(device->devname, "/dev/"));

        *devname = device->devname;

        return 0;
}

static int device_set_sysname(sd_device *device) {
        _cleanup_free_ char *sysname = NULL;
        const char *sysnum = NULL;
        const char *pos;
        size_t len = 0;

        pos = strrchr(device->devpath, '/');
        if (!pos)
                return -EINVAL;
        pos ++;

        /* devpath is not a root directory */
        if (*pos == '\0' || pos <= device->devpath)
                return -EINVAL;

        sysname = strdup(pos);
        if (!sysname)
                return -ENOMEM;

        /* some devices have '!' in their name, change that to '/' */
        while (sysname[len] != '\0') {
                if (sysname[len] == '!')
                        sysname[len] = '/';

                len ++;
        }

        /* trailing number */
        while (len > 0 && isdigit(sysname[--len]))
                sysnum = &sysname[len];

        if (len == 0)
                sysnum = NULL;

        free(device->sysname);
        device->sysname = sysname;
        sysname = NULL;

        device->sysnum = sysnum;

        device->sysname_set = true;

        return 0;
}

_public_ int sd_device_get_sysname(sd_device *device, const char **ret) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(ret, -EINVAL);

        if (!device->sysname_set) {
                r = device_set_sysname(device);
                if (r < 0)
                        return r;
        }

        *ret = device->sysname;

        return 0;
}

_public_ int sd_device_get_sysnum(sd_device *device, const char **ret) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(ret, -EINVAL);

        if (!device->sysname_set) {
                r = device_set_sysname(device);
                if (r < 0)
                        return r;
        }

        *ret = device->sysnum;

        return 0;
}

static bool is_valid_tag(const char *tag) {
        assert(tag);

        return !strchr(tag, ':') && !strchr(tag, ' ');
}

int device_add_tag(sd_device *device, const char *tag) {
        int r;

        assert(device);
        assert(tag);

        if (!is_valid_tag(tag))
                return -EINVAL;

        r = set_ensure_allocated(&device->tags, &string_hash_ops);
        if (r < 0)
                return r;

        r = set_put_strdup(device->tags, tag);
        if (r < 0)
                return r;

        device->tags_generation ++;
        device->property_tags_outdated = true;

        return 0;
}

int device_add_devlink(sd_device *device, const char *devlink) {
        int r;

        assert(device);
        assert(devlink);

        r = set_ensure_allocated(&device->devlinks, &string_hash_ops);
        if (r < 0)
                return r;

        r = set_put_strdup(device->devlinks, devlink);
        if (r < 0)
                return r;

        device->devlinks_generation ++;
        device->property_devlinks_outdated = true;

        return 0;
}

static int device_add_property_internal_from_string(sd_device *device, const char *str) {
        _cleanup_free_ char *key = NULL;
        char *value;

        assert(device);
        assert(str);

        key = strdup(str);
        if (!key)
                return -ENOMEM;

        value = strchr(key, '=');
        if (!value)
                return -EINVAL;

        *value = '\0';

        if (isempty(++value))
                value = NULL;

        return device_add_property_internal(device, key, value);
}

int device_set_usec_initialized(sd_device *device, const char *initialized) {
        uint64_t usec_initialized;
        int r;

        assert(device);
        assert(initialized);

        r = safe_atou64(initialized, &usec_initialized);
        if (r < 0)
                return r;

        r = device_add_property_internal(device, "USEC_INITIALIZED", initialized);
        if (r < 0)
                return r;

        device->usec_initialized = usec_initialized;

        return 0;
}

static int handle_db_line(sd_device *device, char key, const char *value) {
        char *path;
        int r;

        assert(device);
        assert(value);

        switch (key) {
        case 'G':
                r = device_add_tag(device, value);
                if (r < 0)
                        return r;

                break;
        case 'S':
                path = strjoina("/dev/", value);
                r = device_add_devlink(device, path);
                if (r < 0)
                        return r;

                break;
        case 'E':
                r = device_add_property_internal_from_string(device, value);
                if (r < 0)
                        return r;

                break;
        case 'I':
                r = device_set_usec_initialized(device, value);
                if (r < 0)
                        return r;

                break;
        case 'L':
                r = safe_atoi(value, &device->devlink_priority);
                if (r < 0)
                        return r;

                break;
        case 'W':
                r = safe_atoi(value, &device->watch_handle);
                if (r < 0)
                        return r;

                break;
        default:
                log_debug("device db: unknown key '%c'", key);
        }

        return 0;
}

int device_get_id_filename(sd_device *device, const char **ret) {
        assert(device);
        assert(ret);

        if (!device->id_filename) {
                _cleanup_free_ char *id = NULL;
                const char *subsystem;
                dev_t devnum;
                int ifindex, r;

                r = sd_device_get_subsystem(device, &subsystem);
                if (r < 0)
                        return r;

                r = sd_device_get_devnum(device, &devnum);
                if (r < 0)
                        return r;

                r = sd_device_get_ifindex(device, &ifindex);
                if (r < 0)
                        return r;

                if (major(devnum) > 0) {
                        assert(subsystem);

                        /* use dev_t -- b259:131072, c254:0 */
                        r = asprintf(&id, "%c%u:%u",
                                     streq(subsystem, "block") ? 'b' : 'c',
                                     major(devnum), minor(devnum));
                        if (r < 0)
                                return -ENOMEM;
                } else if (ifindex > 0) {
                        /* use netdev ifindex -- n3 */
                        r = asprintf(&id, "n%u", ifindex);
                        if (r < 0)
                                return -ENOMEM;
                } else {
                        /* use $subsys:$sysname -- pci:0000:00:1f.2
                         * sysname() has '!' translated, get it from devpath
                         */
                        const char *sysname;

                        sysname = basename(device->devpath);
                        if (!sysname)
                                return -EINVAL;

                        if (!subsystem)
                                return -EINVAL;

                        r = asprintf(&id, "+%s:%s", subsystem, sysname);
                        if (r < 0)
                                return -ENOMEM;
                }

                device->id_filename = id;
                id = NULL;
        }

        *ret = device->id_filename;

        return 0;
}

int device_read_db_aux(sd_device *device, bool force) {
        _cleanup_free_ char *db = NULL;
        char *path;
        const char *id, *value;
        char key;
        size_t db_len;
        unsigned i;
        int r;

        enum {
                PRE_KEY,
                KEY,
                PRE_VALUE,
                VALUE,
                INVALID_LINE,
        } state = PRE_KEY;

        if (device->db_loaded || (!force && device->sealed))
                return 0;

        device->db_loaded = true;

        r = device_get_id_filename(device, &id);
        if (r < 0)
                return r;

        path = strjoina("/run/udev/data/", id);

        r = read_full_file(path, &db, &db_len);
        if (r < 0) {
                if (r == -ENOENT)
                        return 0;
                else {
                        log_debug("sd-device: failed to read db '%s': %s", path, strerror(-r));
                        return r;
                }
        }

        /* devices with a database entry are initialized */
        device->is_initialized = true;

        for (i = 0; i < db_len; i++) {
                switch (state) {
                case PRE_KEY:
                        if (!strchr(NEWLINE, db[i])) {
                                key = db[i];

                                state = KEY;
                        }

                        break;
                case KEY:
                        if (db[i] != ':') {
                                log_debug("sd-device: ignoring invalid db entry with key '%c'", key);

                                state = INVALID_LINE;
                        } else {
                                db[i] = '\0';

                                state = PRE_VALUE;
                        }

                        break;
                case PRE_VALUE:
                        value = &db[i];

                        state = VALUE;

                        break;
                case INVALID_LINE:
                        if (strchr(NEWLINE, db[i]))
                                state = PRE_KEY;

                        break;
                case VALUE:
                        if (strchr(NEWLINE, db[i])) {
                                db[i] = '\0';
                                r = handle_db_line(device, key, value);
                                if (r < 0)
                                        log_debug("sd-device: failed to handle db entry '%c:%s': %s", key, value, strerror(-r));

                                state = PRE_KEY;
                        }

                        break;
                default:
                        assert_not_reached("invalid state when parsing db");
                }
        }

        return 0;
}

static int device_read_db(sd_device *device) {
        return device_read_db_aux(device, false);
}

_public_ int sd_device_get_is_initialized(sd_device *device, int *initialized) {
        int r;

        assert_return(device, -EINVAL);
        assert_return(initialized, -EINVAL);

        r = device_read_db(device);
        if (r < 0)
                return r;

        *initialized = device->is_initialized;

        return 0;
}

_public_ int sd_device_get_usec_since_initialized(sd_device *device, uint64_t *usec) {
        usec_t now_ts;
        int r;

        assert_return(device, -EINVAL);
        assert_return(usec, -EINVAL);

        r = device_read_db(device);
        if (r < 0)
                return r;

        if (!device->is_initialized)
                return -EBUSY;

        if (!device->usec_initialized)
                return -ENODATA;

        now_ts = now(clock_boottime_or_monotonic());

        if (now_ts < device->usec_initialized)
                return -EIO;

        *usec = now_ts - device->usec_initialized;

        return 0;
}

_public_ const char *sd_device_get_tag_first(sd_device *device) {
        void *v;

        assert_return(device, NULL);

        (void) device_read_db(device);

        device->tags_iterator_generation = device->tags_generation;
        device->tags_iterator = ITERATOR_FIRST;

        set_iterate(device->tags, &device->tags_iterator, &v);
        return v;
}

_public_ const char *sd_device_get_tag_next(sd_device *device) {
        void *v;

        assert_return(device, NULL);

        (void) device_read_db(device);

        if (device->tags_iterator_generation != device->tags_generation)
                return NULL;

        set_iterate(device->tags, &device->tags_iterator, &v);
        return v;
}

_public_ const char *sd_device_get_devlink_first(sd_device *device) {
        void *v;

        assert_return(device, NULL);

        (void) device_read_db(device);

        device->devlinks_iterator_generation = device->devlinks_generation;
        device->devlinks_iterator = ITERATOR_FIRST;

        set_iterate(device->devlinks, &device->devlinks_iterator, &v);
        return v;
}

_public_ const char *sd_device_get_devlink_next(sd_device *device) {
        void *v;

        assert_return(device, NULL);

        (void) device_read_db(device);

        if (device->devlinks_iterator_generation != device->devlinks_generation)
                return NULL;

        set_iterate(device->devlinks, &device->devlinks_iterator, &v);
        return v;
}

static int device_properties_prepare(sd_device *device) {
        int r;

        assert(device);

        r = device_read_uevent_file(device);
        if (r < 0)
                return r;

        r = device_read_db(device);
        if (r < 0)
                return r;

        if (device->property_devlinks_outdated) {
                char *devlinks = NULL;
                const char *devlink;

                devlink = sd_device_get_devlink_first(device);
                if (devlink)
                        devlinks = strdupa(devlink);

                while ((devlink = sd_device_get_devlink_next(device)))
                        devlinks = strjoina(devlinks, " ", devlink);

                r = device_add_property_internal(device, "DEVLINKS", devlinks);
                if (r < 0)
                        return r;

                device->property_devlinks_outdated = false;
        }

        if (device->property_tags_outdated) {
                char *tags = NULL;
                const char *tag;

                tag = sd_device_get_tag_first(device);
                if (tag)
                        tags = strjoina(":", tag);

                while ((tag = sd_device_get_tag_next(device)))
                        tags = strjoina(tags, ":", tag);

                tags = strjoina(tags, ":");

                r = device_add_property_internal(device, "TAGS", tags);
                if (r < 0)
                        return r;

                device->property_tags_outdated = false;
        }

        return 0;
}

_public_ const char *sd_device_get_property_first(sd_device *device, const char **_value) {
        const char *key;
        const char *value;
        int r;

        assert_return(device, NULL);

        r = device_properties_prepare(device);
        if (r < 0)
                return NULL;

        device->properties_iterator_generation = device->properties_generation;
        device->properties_iterator = ITERATOR_FIRST;

        ordered_hashmap_iterate(device->properties, &device->properties_iterator, (void**)&value, (const void**)&key);

        if (_value)
                *_value = value;

        return key;
}

_public_ const char *sd_device_get_property_next(sd_device *device, const char **_value) {
        const char *key;
        const char *value;
        int r;

        assert_return(device, NULL);

        r = device_properties_prepare(device);
        if (r < 0)
                return NULL;

        if (device->properties_iterator_generation != device->properties_generation)
                return NULL;

        ordered_hashmap_iterate(device->properties, &device->properties_iterator, (void**)&value, (const void**)&key);

        if (_value)
                *_value = value;

        return key;
}

static int device_sysattrs_read_all(sd_device *device) {
        _cleanup_closedir_ DIR *dir = NULL;
        const char *syspath;
        struct dirent *dent;
        int r;

        assert(device);

        if (device->sysattrs_read)
                return 0;

        r = sd_device_get_syspath(device, &syspath);
        if (r < 0)
                return r;

        dir = opendir(syspath);
        if (!dir)
                return -errno;

        r = set_ensure_allocated(&device->sysattrs, &string_hash_ops);
        if (r < 0)
                return r;

        for (dent = readdir(dir); dent != NULL; dent = readdir(dir)) {
                char *path;
                struct stat statbuf;

                /* only handle symlinks and regular files */
                if (dent->d_type != DT_LNK && dent->d_type != DT_REG)
                        continue;

                path = strjoina(syspath, "/", dent->d_name);

                if (lstat(path, &statbuf) != 0)
                        continue;

                if (!(statbuf.st_mode & S_IRUSR))
                        continue;

                r = set_put_strdup(device->sysattrs, dent->d_name);
                if (r < 0)
                        return r;
        }

        device->sysattrs_read = true;

        return 0;
}

_public_ const char *sd_device_get_sysattr_first(sd_device *device) {
        void *v;
        int r;

        assert_return(device, NULL);

        if (!device->sysattrs_read) {
                r = device_sysattrs_read_all(device);
                if (r < 0) {
                        errno = -r;
                        return NULL;
                }
        }

        device->sysattrs_iterator = ITERATOR_FIRST;

        set_iterate(device->sysattrs, &device->sysattrs_iterator, &v);
        return v;
}

_public_ const char *sd_device_get_sysattr_next(sd_device *device) {
        void *v;

        assert_return(device, NULL);

        if (!device->sysattrs_read)
                return NULL;

        set_iterate(device->sysattrs, &device->sysattrs_iterator, &v);
        return v;
}

_public_ int sd_device_has_tag(sd_device *device, const char *tag) {
        assert_return(device, -EINVAL);
        assert_return(tag, -EINVAL);

        (void) device_read_db(device);

        return !!set_contains(device->tags, tag);
}

_public_ int sd_device_get_property_value(sd_device *device, const char *key, const char **_value) {
        char *value;
        int r;

        assert_return(device, -EINVAL);
        assert_return(key, -EINVAL);
        assert_return(_value, -EINVAL);

        r = device_properties_prepare(device);
        if (r < 0)
                return r;

        value = ordered_hashmap_get(device->properties, key);
        if (!value)
                return -ENOENT;

        *_value = value;

        return 0;
}

/* replaces the value if it already exists */
static int device_add_sysattr_value(sd_device *device, const char *_key, char *value) {
        _cleanup_free_ char *key = NULL;
        _cleanup_free_ char *value_old = NULL;
        int r;

        assert(device);
        assert(_key);

        r = hashmap_ensure_allocated(&device->sysattr_values, &string_hash_ops);
        if (r < 0)
                return r;

        value_old = hashmap_remove2(device->sysattr_values, _key, (void **)&key);
        if (!key) {
                key = strdup(_key);
                if (!key)
                        return -ENOMEM;
        }

        r = hashmap_put(device->sysattr_values, key, value);
        if (r < 0)
                return r;

        key = NULL;

        return 0;
}

static int device_get_sysattr_value(sd_device *device, const char *_key, const char **_value) {
        const char *key = NULL, *value;

        assert(device);
        assert(_key);

        value = hashmap_get2(device->sysattr_values, _key, (void **) &key);
        if (!key)
                return -ENOENT;

        if (_value)
                *_value = value;

        return 0;
}

/* We cache all sysattr lookups. If an attribute does not exist, it is stored
 * with a NULL value in the cache, otherwise the returned string is stored */
_public_ int sd_device_get_sysattr_value(sd_device *device, const char *sysattr, const char **_value) {
        _cleanup_free_ char *value = NULL;
        const char *syspath, *cached_value = NULL;
        char *path;
        struct stat statbuf;
        int r;

        assert_return(device, -EINVAL);
        assert_return(sysattr, -EINVAL);

        /* look for possibly already cached result */
        r = device_get_sysattr_value(device, sysattr, &cached_value);
        if (r != -ENOENT) {
                if (r < 0)
                        return r;

                if (!cached_value)
                        /* we looked up the sysattr before and it did not exist */
                        return -ENOENT;

                if (_value)
                        *_value = cached_value;

                return 0;
        }

        r = sd_device_get_syspath(device, &syspath);
        if (r < 0)
                return r;

        path = strjoina(syspath, "/", sysattr);
        r = lstat(path, &statbuf);
        if (r < 0) {
                /* remember that we could not access the sysattr */
                r = device_add_sysattr_value(device, sysattr, NULL);
                if (r < 0)
                        return r;

                return -ENOENT;
        } else if (S_ISLNK(statbuf.st_mode)) {
                /* Some core links return only the last element of the target path,
                 * these are just values, the paths should not be exposed. */
                if (STR_IN_SET(sysattr, "driver", "subsystem", "module")) {
                        r = readlink_value(path, &value);
                        if (r < 0)
                                return r;
                } else
                        return -EINVAL;
        } else if (S_ISDIR(statbuf.st_mode)) {
                /* skip directories */
                return -EINVAL;
        } else if (!(statbuf.st_mode & S_IRUSR)) {
                /* skip non-readable files */
                return -EPERM;
        } else {
                size_t size;

                /* read attribute value */
                r = read_full_file(path, &value, &size);
                if (r < 0)
                        return r;

                /* drop trailing newlines */
                while (size > 0 && value[--size] == '\n')
                        value[size] = '\0';
        }

        r = device_add_sysattr_value(device, sysattr, value);
        if (r < 0)
                return r;

        *_value = value;
        value = NULL;

        return 0;
}

static void device_remove_sysattr_value(sd_device *device, const char *_key) {
        _cleanup_free_ char *key = NULL;
        _cleanup_free_ char *value = NULL;

        assert(device);
        assert(_key);

        value = hashmap_remove2(device->sysattr_values, _key, (void **) &key);

        return;
}

/* set the attribute and save it in the cache. If a NULL value is passed the
 * attribute is cleared from the cache */
_public_ int sd_device_set_sysattr_value(sd_device *device, const char *sysattr, char *_value) {
        _cleanup_close_ int fd = -1;
        _cleanup_free_ char *value = NULL;
        const char *syspath;
        char *path;
        struct stat statbuf;
        size_t value_len = 0;
        ssize_t size;
        int r;

        assert_return(device, -EINVAL);
        assert_return(sysattr, -EINVAL);

        if (!_value) {
                device_remove_sysattr_value(device, sysattr);

                return 0;
        }

        r = sd_device_get_syspath(device, &syspath);
        if (r < 0)
                return r;

        path = strjoina(syspath, "/", sysattr);
        r = lstat(path, &statbuf);
        if (r < 0) {
                value = strdup("");
                if (!value)
                        return -ENOMEM;

                r = device_add_sysattr_value(device, sysattr, value);
                if (r < 0)
                        return r;

                return -ENXIO;
        }

        if (S_ISLNK(statbuf.st_mode))
                return -EINVAL;

        /* skip directories */
        if (S_ISDIR(statbuf.st_mode))
                return -EISDIR;

        /* skip non-readable files */
        if ((statbuf.st_mode & S_IRUSR) == 0)
                return -EACCES;

        value_len = strlen(_value);

        /* drop trailing newlines */
        while (value_len > 0 && _value[value_len - 1] == '\n')
                _value[--value_len] = '\0';

        /* value length is limited to 4k */
        if (value_len > 4096)
                return -EINVAL;

        fd = open(path, O_WRONLY | O_CLOEXEC);
        if (fd < 0)
                return -errno;

        value = strdup(_value);
        if (!value)
                return -ENOMEM;

        size = write(fd, value, value_len);
        if (size < 0)
                return -errno;

        if ((size_t)size != value_len)
                return -EIO;

        r = device_add_sysattr_value(device, sysattr, value);
        if (r < 0)
                return r;

        value = NULL;

        return 0;
}