init/devices.cpp

/*
 * Copyright (C) 2007-2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "devices.h"

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <fnmatch.h>
#include <grp.h>
#include <libgen.h>
#include <linux/netlink.h>
#include <pwd.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/sendfile.h>
#include <sys/socket.h>
#include <sys/sysmacros.h>
#include <sys/time.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>

#include <algorithm>
#include <memory>
#include <thread>

#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <cutils/uevent.h>
#include <private/android_filesystem_config.h>
#include <selinux/android.h>
#include <selinux/label.h>
#include <selinux/selinux.h>

#include "keyword_map.h"
#include "ueventd.h"
#include "util.h"

#ifdef _INIT_INIT_H
#error "Do not include init.h in files used by ueventd or watchdogd; it will expose init's globals"
#endif

static selabel_handle* sehandle;

static android::base::unique_fd device_fd;

Permissions::Permissions(const std::string& name, mode_t perm, uid_t uid, gid_t gid)
    : name_(name), perm_(perm), uid_(uid), gid_(gid), prefix_(false), wildcard_(false) {
    // If the first * is the last character, then we'll treat name_ as a prefix
    // Otherwise, if a * is present, then we do a full fnmatch().
    auto wildcard_position = name_.find('*');
    if (wildcard_position == name_.length() - 1) {
        prefix_ = true;
        name_.pop_back();
    } else if (wildcard_position != std::string::npos) {
        wildcard_ = true;
    }
}

bool Permissions::Match(const std::string& path) const {
    if (prefix_) {
        return android::base::StartsWith(path, name_.c_str());
    } else if (wildcard_) {
        return fnmatch(name_.c_str(), path.c_str(), FNM_PATHNAME) == 0;
    } else {
        return path == name_;
    }

    return false;
}

bool SysfsPermissions::MatchWithSubsystem(const std::string& path,
                                          const std::string& subsystem) const {
    std::string path_basename = android::base::Basename(path);
    if (name().find(subsystem) != std::string::npos) {
        if (Match("/sys/class/" + subsystem + "/" + path_basename)) return true;
        if (Match("/sys/bus/" + subsystem + "/devices/" + path_basename)) return true;
    }
    return Match(path);
}

void SysfsPermissions::SetPermissions(const std::string& path) const {
    std::string attribute_file = path + "/" + attribute_;
    LOG(INFO) << "fixup " << attribute_file << " " << uid() << " " << gid() << " " << std::oct
              << perm();
    chown(attribute_file.c_str(), uid(), gid());
    chmod(attribute_file.c_str(), perm());
}

// TODO: Move these to be member variables of a future devices class.
std::vector<Permissions> dev_permissions;
std::vector<SysfsPermissions> sysfs_permissions;

bool ParsePermissionsLine(std::vector<std::string>&& args, std::string* err, bool is_sysfs) {
    if (is_sysfs && args.size() != 5) {
        *err = "/sys/ lines must have 5 entries";
        return false;
    }

    if (!is_sysfs && args.size() != 4) {
        *err = "/dev/ lines must have 4 entries";
        return false;
    }

    auto it = args.begin();
    const std::string& name = *it++;

    std::string sysfs_attribute;
    if (is_sysfs) sysfs_attribute = *it++;

    // args is now common to both sys and dev entries and contains: <perm> <uid> <gid>
    std::string& perm_string = *it++;
    char* end_pointer = 0;
    mode_t perm = strtol(perm_string.c_str(), &end_pointer, 8);
    if (end_pointer == nullptr || *end_pointer != '\0') {
        *err = "invalid mode '" + perm_string + "'";
        return false;
    }

    std::string& uid_string = *it++;
    passwd* pwd = getpwnam(uid_string.c_str());
    if (!pwd) {
        *err = "invalid uid '" + uid_string + "'";
        return false;
    }
    uid_t uid = pwd->pw_uid;

    std::string& gid_string = *it++;
    struct group* grp = getgrnam(gid_string.c_str());
    if (!grp) {
        *err = "invalid gid '" + gid_string + "'";
        return false;
    }
    gid_t gid = grp->gr_gid;

    if (is_sysfs) {
        sysfs_permissions.emplace_back(name, sysfs_attribute, perm, uid, gid);
    } else {
        dev_permissions.emplace_back(name, perm, uid, gid);
    }
    return true;
}

// TODO: Move this to be a member variable of a future devices class.
static std::vector<Subsystem> subsystems;

std::string Subsystem::ParseDevPath(uevent* uevent) const {
    std::string devname = devname_source_ == DevnameSource::DEVNAME_UEVENT_DEVNAME
                              ? uevent->device_name
                              : android::base::Basename(uevent->path);

    return dir_name_ + "/" + devname;
}

bool SubsystemParser::ParseSection(std::vector<std::string>&& args, const std::string& filename,
                                   int line, std::string* err) {
    if (args.size() != 2) {
        *err = "subsystems must have exactly one name";
        return false;
    }

    if (std::find(subsystems.begin(), subsystems.end(), args[1]) != subsystems.end()) {
        *err = "ignoring duplicate subsystem entry";
        return false;
    }

    subsystem_.name_ = args[1];

    return true;
}

bool SubsystemParser::ParseDevName(std::vector<std::string>&& args, std::string* err) {
    if (args[1] == "uevent_devname") {
        subsystem_.devname_source_ = Subsystem::DevnameSource::DEVNAME_UEVENT_DEVNAME;
        return true;
    }
    if (args[1] == "uevent_devpath") {
        subsystem_.devname_source_ = Subsystem::DevnameSource::DEVNAME_UEVENT_DEVPATH;
        return true;
    }

    *err = "invalid devname '" + args[1] + "'";
    return false;
}

bool SubsystemParser::ParseDirName(std::vector<std::string>&& args, std::string* err) {
    if (args[1].front() != '/') {
        *err = "dirname '" + args[1] + " ' does not start with '/'";
        return false;
    }

    subsystem_.dir_name_ = args[1];
    return true;
}

bool SubsystemParser::ParseLineSection(std::vector<std::string>&& args, int line, std::string* err) {
    using OptionParser =
        bool (SubsystemParser::*)(std::vector<std::string> && args, std::string * err);
    static class OptionParserMap : public KeywordMap<OptionParser> {
      private:
        const Map& map() const override {
            // clang-format off
            static const Map option_parsers = {
                {"devname",     {1,     1,      &SubsystemParser::ParseDevName}},
                {"dirname",     {1,     1,      &SubsystemParser::ParseDirName}},
            };
            // clang-format on
            return option_parsers;
        }
    } parser_map;

    auto parser = parser_map.FindFunction(args, err);

    if (!parser) {
        return false;
    }

    return (this->*parser)(std::move(args), err);
}

void SubsystemParser::EndSection() {
    subsystems.emplace_back(std::move(subsystem_));
}

static void fixup_sys_permissions(const std::string& upath, const std::string& subsystem) {
    // upaths omit the "/sys" that paths in this list
    // contain, so we prepend it...
    std::string path = "/sys" + upath;

    for (const auto& s : sysfs_permissions) {
        if (s.MatchWithSubsystem(path, subsystem)) s.SetPermissions(path);
    }

    if (access(path.c_str(), F_OK) == 0) {
        LOG(VERBOSE) << "restorecon_recursive: " << path;
        selinux_android_restorecon(path.c_str(), SELINUX_ANDROID_RESTORECON_RECURSE);
    }
}

static std::tuple<mode_t, uid_t, gid_t> get_device_permissions(
    const std::string& path, const std::vector<std::string>& links) {
    // Search the perms list in reverse so that ueventd.$hardware can override ueventd.rc.
    for (auto it = dev_permissions.rbegin(); it != dev_permissions.rend(); ++it) {
        if (it->Match(path) || std::any_of(links.begin(), links.end(),
                                           [it](const auto& link) { return it->Match(link); })) {
            return {it->perm(), it->uid(), it->gid()};
        }
    }
    /* Default if nothing found. */
    return {0600, 0, 0};
}

static void make_device(const std::string& path, int block, int major, int minor,
                        const std::vector<std::string>& links) {
    dev_t dev;
    char *secontext = NULL;

    auto [mode, uid, gid] = get_device_permissions(path, links);
    mode |= (block ? S_IFBLK : S_IFCHR);

    if (sehandle) {
        std::vector<const char*> c_links;
        for (const auto& link : links) {
            c_links.emplace_back(link.c_str());
        }
        c_links.emplace_back(nullptr);
        if (selabel_lookup_best_match(sehandle, &secontext, path.c_str(), &c_links[0], mode)) {
            PLOG(ERROR) << "Device '" << path << "' not created; cannot find SELinux label";
            return;
        }
        setfscreatecon(secontext);
    }

    dev = makedev(major, minor);
    /* Temporarily change egid to avoid race condition setting the gid of the
     * device node. Unforunately changing the euid would prevent creation of
     * some device nodes, so the uid has to be set with chown() and is still
     * racy. Fixing the gid race at least fixed the issue with system_server
     * opening dynamic input devices under the AID_INPUT gid. */
    if (setegid(gid)) {
        PLOG(ERROR) << "setegid(" << gid << ") for " << path << " device failed";
        goto out;
    }
    /* If the node already exists update its SELinux label to handle cases when
     * it was created with the wrong context during coldboot procedure. */
    if (mknod(path.c_str(), mode, dev) && (errno == EEXIST) && secontext) {
        char* fcon = nullptr;
        int rc = lgetfilecon(path.c_str(), &fcon);
        if (rc < 0) {
            PLOG(ERROR) << "Cannot get SELinux label on '" << path << "' device";
            goto out;
        }

        bool different = strcmp(fcon, secontext) != 0;
        freecon(fcon);

        if (different && lsetfilecon(path.c_str(), secontext)) {
            PLOG(ERROR) << "Cannot set '" << secontext << "' SELinux label on '" << path << "' device";
        }
    }

out:
    chown(path.c_str(), uid, -1);
    if (setegid(AID_ROOT)) {
        PLOG(FATAL) << "setegid(AID_ROOT) failed";
    }

    if (secontext) {
        freecon(secontext);
        setfscreatecon(NULL);
    }
}

// TODO: Move this to be a member variable of a future devices class.
std::vector<std::string> platform_devices;

// Given a path that may start with a platform device, find the length of the
// platform device prefix.  If it doesn't start with a platform device, return false
bool find_platform_device(const std::string& path, std::string* out_path) {
    out_path->clear();
    // platform_devices is searched backwards, since parents are added before their children,
    // and we want to match as deep of a child as we can.
    for (auto it = platform_devices.rbegin(); it != platform_devices.rend(); ++it) {
        auto platform_device_path_length = it->length();
        if (platform_device_path_length < path.length() &&
            path[platform_device_path_length] == '/' &&
            android::base::StartsWith(path, it->c_str())) {
            *out_path = *it;
            return true;
        }
    }
    return false;
}

/* Given a path that may start with a PCI device, populate the supplied buffer
 * with the PCI domain/bus number and the peripheral ID and return 0.
 * If it doesn't start with a PCI device, or there is some error, return -1 */
static bool find_pci_device_prefix(const std::string& path, std::string* result) {
    result->clear();

    if (!android::base::StartsWith(path, "/devices/pci")) return false;

    /* Beginning of the prefix is the initial "pci" after "/devices/" */
    std::string::size_type start = 9;

    /* End of the prefix is two path '/' later, capturing the domain/bus number
     * and the peripheral ID. Example: pci0000:00/0000:00:1f.2 */
    auto end = path.find('/', start);
    if (end == std::string::npos) return false;

    end = path.find('/', end + 1);
    if (end == std::string::npos) return false;

    auto length = end - start;
    if (length <= 4) {
        // The minimum string that will get to this check is 'pci/', which is malformed,
        // so return false
        return false;
    }

    *result = path.substr(start, length);
    return true;
}

/* Given a path that may start with a virtual block device, populate
 * the supplied buffer with the virtual block device ID and return 0.
 * If it doesn't start with a virtual block device, or there is some
 * error, return -1 */
static bool find_vbd_device_prefix(const std::string& path, std::string* result) {
    result->clear();

    if (!android::base::StartsWith(path, "/devices/vbd-")) return false;

    /* Beginning of the prefix is the initial "vbd-" after "/devices/" */
    std::string::size_type start = 13;

    /* End of the prefix is one path '/' later, capturing the
       virtual block device ID. Example: 768 */
    auto end = path.find('/', start);
    if (end == std::string::npos) return false;

    auto length = end - start;
    if (length == 0) return false;

    *result = path.substr(start, length);
    return true;
}

void parse_event(const char* msg, uevent* uevent) {
    uevent->partition_num = -1;
    uevent->major = -1;
    uevent->minor = -1;
    // currently ignoring SEQNUM
    while(*msg) {
        if(!strncmp(msg, "ACTION=", 7)) {
            msg += 7;
            uevent->action = msg;
        } else if(!strncmp(msg, "DEVPATH=", 8)) {
            msg += 8;
            uevent->path = msg;
        } else if(!strncmp(msg, "SUBSYSTEM=", 10)) {
            msg += 10;
            uevent->subsystem = msg;
        } else if(!strncmp(msg, "FIRMWARE=", 9)) {
            msg += 9;
            uevent->firmware = msg;
        } else if(!strncmp(msg, "MAJOR=", 6)) {
            msg += 6;
            uevent->major = atoi(msg);
        } else if(!strncmp(msg, "MINOR=", 6)) {
            msg += 6;
            uevent->minor = atoi(msg);
        } else if(!strncmp(msg, "PARTN=", 6)) {
            msg += 6;
            uevent->partition_num = atoi(msg);
        } else if(!strncmp(msg, "PARTNAME=", 9)) {
            msg += 9;
            uevent->partition_name = msg;
        } else if(!strncmp(msg, "DEVNAME=", 8)) {
            msg += 8;
            uevent->device_name = msg;
        }

        // advance to after the next \0
        while(*msg++)
            ;
    }

    if (LOG_UEVENTS) {
        LOG(INFO) << "event { '" << uevent->action << "', '" << uevent->path << "', '"
                  << uevent->subsystem << "', '" << uevent->firmware << "', " << uevent->major
                  << ", " << uevent->minor << " }";
    }
}

std::vector<std::string> get_character_device_symlinks(uevent* uevent) {
    std::string parent_device;
    if (!find_platform_device(uevent->path, &parent_device)) return {};

    // skip path to the parent driver
    std::string path = uevent->path.substr(parent_device.length());

    if (!android::base::StartsWith(path, "/usb")) return {};

    // skip root hub name and device. use device interface
    // skip 3 slashes, including the first / by starting the search at the 1st character, not 0th.
    // then extract what comes between the 3rd and 4th slash
    // e.g. "/usb/usb_device/name/tty2-1:1.0" -> "name"

    std::string::size_type start = 0;
    start = path.find('/', start + 1);
    if (start == std::string::npos) return {};

    start = path.find('/', start + 1);
    if (start == std::string::npos) return {};

    auto end = path.find('/', start + 1);
    if (end == std::string::npos) return {};

    start++;  // Skip the first '/'

    auto length = end - start;
    if (length == 0) return {};

    auto name_string = path.substr(start, length);

    std::vector<std::string> links;
    links.emplace_back("/dev/usb/" + uevent->subsystem + name_string);

    mkdir("/dev/usb", 0755);

    return links;
}

// replaces any unacceptable characters with '_', the
// length of the resulting string is equal to the input string
void sanitize_partition_name(std::string* string) {
    const char* accept =
        "abcdefghijklmnopqrstuvwxyz"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "0123456789"
        "_-.";

    if (!string) return;

    std::string::size_type pos = 0;
    while ((pos = string->find_first_not_of(accept, pos)) != std::string::npos) {
        (*string)[pos] = '_';
    }
}

std::vector<std::string> get_block_device_symlinks(uevent* uevent) {
    std::string device;
    std::string type;

    if (find_platform_device(uevent->path, &device)) {
        // Skip /devices/platform or /devices/ if present
        static const std::string devices_platform_prefix = "/devices/platform/";
        static const std::string devices_prefix = "/devices/";

        if (android::base::StartsWith(device, devices_platform_prefix.c_str())) {
            device = device.substr(devices_platform_prefix.length());
        } else if (android::base::StartsWith(device, devices_prefix.c_str())) {
            device = device.substr(devices_prefix.length());
        }

        type = "platform";
    } else if (find_pci_device_prefix(uevent->path, &device)) {
        type = "pci";
    } else if (find_vbd_device_prefix(uevent->path, &device)) {
        type = "vbd";
    } else {
        return {};
    }

    std::vector<std::string> links;

    LOG(VERBOSE) << "found " << type << " device " << device;

    auto link_path = "/dev/block/" + type + "/" + device;

    if (!uevent->partition_name.empty()) {
        std::string partition_name_sanitized(uevent->partition_name);
        sanitize_partition_name(&partition_name_sanitized);
        if (partition_name_sanitized != uevent->partition_name) {
            LOG(VERBOSE) << "Linking partition '" << uevent->partition_name << "' as '"
                         << partition_name_sanitized << "'";
        }
        links.emplace_back(link_path + "/by-name/" + partition_name_sanitized);
    }

    if (uevent->partition_num >= 0) {
        links.emplace_back(link_path + "/by-num/p" + std::to_string(uevent->partition_num));
    }

    auto last_slash = uevent->path.rfind('/');
    links.emplace_back(link_path + "/" + uevent->path.substr(last_slash + 1));

    return links;
}

static void make_link_init(const std::string& oldpath, const std::string& newpath) {
    if (mkdir_recursive(dirname(newpath.c_str()), 0755, sehandle)) {
        PLOG(ERROR) << "Failed to create directory " << dirname(newpath.c_str());
    }

    if (symlink(oldpath.c_str(), newpath.c_str()) && errno != EEXIST) {
        PLOG(ERROR) << "Failed to symlink " << oldpath << " to " << newpath;
    }
}

static void remove_link(const std::string& oldpath, const std::string& newpath) {
    std::string path;
    if (android::base::Readlink(newpath, &path) && path == oldpath) unlink(newpath.c_str());
}

static void handle_device(const std::string& action, const std::string& devpath, int block,
                          int major, int minor, const std::vector<std::string>& links) {
    if (action == "add") {
        make_device(devpath, block, major, minor, links);
        for (const auto& link : links) {
            make_link_init(devpath, link);
        }
    }

    if (action == "remove") {
        for (const auto& link : links) {
            remove_link(devpath, link);
        }
        unlink(devpath.c_str());
    }
}

void handle_platform_device_event(uevent* uevent) {
    if (uevent->action == "add") {
        platform_devices.emplace_back(uevent->path);
    } else if (uevent->action == "remove") {
        auto it = std::find(platform_devices.begin(), platform_devices.end(), uevent->path);
        if (it != platform_devices.end()) platform_devices.erase(it);
    }
}

static void handle_block_device_event(uevent* uevent) {
    // if it's not a /dev device, nothing to do
    if (uevent->major < 0 || uevent->minor < 0) return;

    const char* base = "/dev/block/";
    make_dir(base, 0755, sehandle);

    std::string name = android::base::Basename(uevent->path);
    std::string devpath = base + name;

    std::vector<std::string> links;
    if (android::base::StartsWith(uevent->path, "/devices")) {
        links = get_block_device_symlinks(uevent);
    }

    handle_device(uevent->action, devpath, 1, uevent->major, uevent->minor, links);
}

static void handle_generic_device_event(uevent* uevent) {
    // if it's not a /dev device, nothing to do
    if (uevent->major < 0 || uevent->minor < 0) return;

    std::string devpath;

    if (android::base::StartsWith(uevent->subsystem, "usb")) {
        if (uevent->subsystem == "usb") {
            if (!uevent->device_name.empty()) {
                devpath = "/dev/" + uevent->device_name;
            } else {
                // This imitates the file system that would be created
                // if we were using devfs instead.
                // Minors are broken up into groups of 128, starting at "001"
                int bus_id = uevent->minor / 128 + 1;
                int device_id = uevent->minor % 128 + 1;
                devpath = android::base::StringPrintf("/dev/bus/usb/%03d/%03d", bus_id, device_id);
            }
        } else {
            // ignore other USB events
            return;
        }
    } else if (auto subsystem = std::find(subsystems.begin(), subsystems.end(), uevent->subsystem);
               subsystem != subsystems.end()) {
        devpath = subsystem->ParseDevPath(uevent);
    } else {
        devpath = "/dev/" + android::base::Basename(uevent->path);
    }

    mkdir_recursive(android::base::Dirname(devpath), 0755, sehandle);

    auto links = get_character_device_symlinks(uevent);

    handle_device(uevent->action, devpath, 0, uevent->major, uevent->minor, links);
}

static void handle_device_event(struct uevent *uevent)
{
    if (uevent->action == "add" || uevent->action == "change" || uevent->action == "online") {
        fixup_sys_permissions(uevent->path, uevent->subsystem);
    }

    if (uevent->subsystem == "block") {
        handle_block_device_event(uevent);
    } else if (uevent->subsystem == "platform") {
        handle_platform_device_event(uevent);
    } else {
        handle_generic_device_event(uevent);
    }
}

static void load_firmware(uevent* uevent, const std::string& root,
                          int fw_fd, size_t fw_size,
                          int loading_fd, int data_fd) {
    // Start transfer.
    android::base::WriteFully(loading_fd, "1", 1);

    // Copy the firmware.
    int rc = sendfile(data_fd, fw_fd, nullptr, fw_size);
    if (rc == -1) {
        PLOG(ERROR) << "firmware: sendfile failed { '" << root << "', '" << uevent->firmware << "' }";
    }

    // Tell the firmware whether to abort or commit.
    const char* response = (rc != -1) ? "0" : "-1";
    android::base::WriteFully(loading_fd, response, strlen(response));
}

static int is_booting() {
    return access("/dev/.booting", F_OK) == 0;
}

static void process_firmware_event(uevent* uevent) {
    int booting = is_booting();

    LOG(INFO) << "firmware: loading '" << uevent->firmware << "' for '" << uevent->path << "'";

    std::string root = "/sys" + uevent->path;
    std::string loading = root + "/loading";
    std::string data = root + "/data";

    android::base::unique_fd loading_fd(open(loading.c_str(), O_WRONLY|O_CLOEXEC));
    if (loading_fd == -1) {
        PLOG(ERROR) << "couldn't open firmware loading fd for " << uevent->firmware;
        return;
    }

    android::base::unique_fd data_fd(open(data.c_str(), O_WRONLY|O_CLOEXEC));
    if (data_fd == -1) {
        PLOG(ERROR) << "couldn't open firmware data fd for " << uevent->firmware;
        return;
    }

    static const char* firmware_dirs[] = {"/etc/firmware/", "/vendor/firmware/",
                                          "/firmware/image/"};

try_loading_again:
    for (size_t i = 0; i < arraysize(firmware_dirs); i++) {
        std::string file = firmware_dirs[i] + uevent->firmware;
        android::base::unique_fd fw_fd(open(file.c_str(), O_RDONLY|O_CLOEXEC));
        struct stat sb;
        if (fw_fd != -1 && fstat(fw_fd, &sb) != -1) {
            load_firmware(uevent, root, fw_fd, sb.st_size, loading_fd, data_fd);
            return;
        }
    }

    if (booting) {
        // If we're not fully booted, we may be missing
        // filesystems needed for firmware, wait and retry.
        std::this_thread::sleep_for(100ms);
        booting = is_booting();
        goto try_loading_again;
    }

    LOG(ERROR) << "firmware: could not find firmware for " << uevent->firmware;

    // Write "-1" as our response to the kernel's firmware request, since we have nothing for it.
    write(loading_fd, "-1", 2);
}

static void handle_firmware_event(uevent* uevent) {
    if (uevent->subsystem != "firmware" || uevent->action != "add") return;

    // Loading the firmware in a child means we can do that in parallel...
    // (We ignore SIGCHLD rather than wait for our children.)
    pid_t pid = fork();
    if (pid == 0) {
        Timer t;
        process_firmware_event(uevent);
        LOG(INFO) << "loading " << uevent->path << " took " << t;
        _exit(EXIT_SUCCESS);
    } else if (pid == -1) {
        PLOG(ERROR) << "could not fork to process firmware event for " << uevent->firmware;
    }
}

static bool inline should_stop_coldboot(coldboot_action_t act)
{
    return (act == COLDBOOT_STOP || act == COLDBOOT_FINISH);
}

#define UEVENT_MSG_LEN  2048

static inline coldboot_action_t handle_device_fd_with(
        std::function<coldboot_action_t(uevent* uevent)> handle_uevent)
{
    char msg[UEVENT_MSG_LEN+2];
    int n;
    while ((n = uevent_kernel_multicast_recv(device_fd, msg, UEVENT_MSG_LEN)) > 0) {
        if(n >= UEVENT_MSG_LEN)   /* overflow -- discard */
            continue;

        msg[n] = '\0';
        msg[n+1] = '\0';

        uevent uevent;
        parse_event(msg, &uevent);
        coldboot_action_t act = handle_uevent(&uevent);
        if (should_stop_coldboot(act))
            return act;
    }

    return COLDBOOT_CONTINUE;
}

coldboot_action_t handle_device_fd(coldboot_callback fn)
{
    coldboot_action_t ret = handle_device_fd_with(
        [&](uevent* uevent) -> coldboot_action_t {
            // default is to always create the devices
            coldboot_action_t act = COLDBOOT_CREATE;
            if (fn) {
                act = fn(uevent);
            }

            if (act == COLDBOOT_CREATE || act == COLDBOOT_STOP) {
                handle_device_event(uevent);
                handle_firmware_event(uevent);
            }

            return act;
        });

    return ret;
}

/* Coldboot walks parts of the /sys tree and pokes the uevent files
** to cause the kernel to regenerate device add events that happened
** before init's device manager was started
**
** We drain any pending events from the netlink socket every time
** we poke another uevent file to make sure we don't overrun the
** socket's buffer.
*/

static coldboot_action_t do_coldboot(DIR *d, coldboot_callback fn)
{
    struct dirent *de;
    int dfd, fd;
    coldboot_action_t act = COLDBOOT_CONTINUE;

    dfd = dirfd(d);

    fd = openat(dfd, "uevent", O_WRONLY);
    if (fd >= 0) {
        write(fd, "add\n", 4);
        close(fd);
        act = handle_device_fd(fn);
        if (should_stop_coldboot(act))
            return act;
    }

    while (!should_stop_coldboot(act) && (de = readdir(d))) {
        DIR *d2;

        if(de->d_type != DT_DIR || de->d_name[0] == '.')
            continue;

        fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY);
        if(fd < 0)
            continue;

        d2 = fdopendir(fd);
        if(d2 == 0)
            close(fd);
        else {
            act = do_coldboot(d2, fn);
            closedir(d2);
        }
    }

    // default is always to continue looking for uevents
    return act;
}

static coldboot_action_t coldboot(const char *path, coldboot_callback fn)
{
    std::unique_ptr<DIR, decltype(&closedir)> d(opendir(path), closedir);
    if (d) {
        return do_coldboot(d.get(), fn);
    }

    return COLDBOOT_CONTINUE;
}

void device_init(const char* path, coldboot_callback fn) {
    if (!sehandle) {
        sehandle = selinux_android_file_context_handle();
    }
    // open uevent socket and selinux status only if it hasn't been
    // done before
    if (device_fd == -1) {
        /* is 256K enough? udev uses 16MB! */
        device_fd.reset(uevent_open_socket(256 * 1024, true));
        if (device_fd == -1) {
            return;
        }
        fcntl(device_fd, F_SETFL, O_NONBLOCK);
    }

    if (access(COLDBOOT_DONE, F_OK) == 0) {
        LOG(VERBOSE) << "Skipping coldboot, already done!";
        return;
    }

    Timer t;
    coldboot_action_t act;
    if (!path) {
        act = coldboot("/sys/class", fn);
        if (!should_stop_coldboot(act)) {
            act = coldboot("/sys/block", fn);
            if (!should_stop_coldboot(act)) {
                act = coldboot("/sys/devices", fn);
            }
        }
    } else {
        act = coldboot(path, fn);
    }

    // If we have a callback, then do as it says. If no, then the default is
    // to always create COLDBOOT_DONE file.
    if (!fn || (act == COLDBOOT_FINISH)) {
        close(open(COLDBOOT_DONE, O_WRONLY|O_CREAT|O_CLOEXEC, 0000));
    }

    LOG(INFO) << "Coldboot took " << t;
}

void device_close() {
    platform_devices.clear();
    device_fd.reset();
}

int get_device_fd() {
    return device_fd;
}