/* SPDX-License-Identifier: LGPL-2.1-or-later */
#pragma once

#include <stdbool.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <unistd.h>

#include "sd-id128.h"

#include "bpf-program.h"
#include "condition.h"
#include "emergency-action.h"
#include "list.h"
#include "show-status.h"
#include "set.h"
#include "unit-file.h"
#include "cgroup.h"

typedef struct UnitRef UnitRef;

typedef enum KillOperation {
        KILL_TERMINATE,
        KILL_TERMINATE_AND_LOG,
        KILL_RESTART,
        KILL_KILL,
        KILL_WATCHDOG,
        _KILL_OPERATION_MAX,
        _KILL_OPERATION_INVALID = -EINVAL,
} KillOperation;

typedef enum CollectMode {
        COLLECT_INACTIVE,
        COLLECT_INACTIVE_OR_FAILED,
        _COLLECT_MODE_MAX,
        _COLLECT_MODE_INVALID = -EINVAL,
} CollectMode;

static inline bool UNIT_IS_ACTIVE_OR_RELOADING(UnitActiveState t) {
        return IN_SET(t, UNIT_ACTIVE, UNIT_RELOADING);
}

static inline bool UNIT_IS_ACTIVE_OR_ACTIVATING(UnitActiveState t) {
        return IN_SET(t, UNIT_ACTIVE, UNIT_ACTIVATING, UNIT_RELOADING);
}

static inline bool UNIT_IS_INACTIVE_OR_DEACTIVATING(UnitActiveState t) {
        return IN_SET(t, UNIT_INACTIVE, UNIT_FAILED, UNIT_DEACTIVATING);
}

static inline bool UNIT_IS_INACTIVE_OR_FAILED(UnitActiveState t) {
        return IN_SET(t, UNIT_INACTIVE, UNIT_FAILED);
}

static inline bool UNIT_IS_LOAD_COMPLETE(UnitLoadState t) {
        return t >= 0 && t < _UNIT_LOAD_STATE_MAX && t != UNIT_STUB && t != UNIT_MERGED;
}

/* Stores the 'reason' a dependency was created as a bit mask, i.e. due to which configuration source it came to be. We
 * use this so that we can selectively flush out parts of dependencies again. Note that the same dependency might be
 * created as a result of multiple "reasons", hence the bitmask. */
typedef enum UnitDependencyMask {
        /* Configured directly by the unit file, .wants/.requires symlink or drop-in, or as an immediate result of a
         * non-dependency option configured that way.  */
        UNIT_DEPENDENCY_FILE               = 1 << 0,

        /* As unconditional implicit dependency (not affected by unit configuration — except by the unit name and
         * type) */
        UNIT_DEPENDENCY_IMPLICIT           = 1 << 1,

        /* A dependency effected by DefaultDependencies=yes. Note that dependencies marked this way are conceptually
         * just a subset of UNIT_DEPENDENCY_FILE, as DefaultDependencies= is itself a unit file setting that can only
         * be set in unit files. We make this two separate bits only to help debugging how dependencies came to be. */
        UNIT_DEPENDENCY_DEFAULT            = 1 << 2,

        /* A dependency created from udev rules */
        UNIT_DEPENDENCY_UDEV               = 1 << 3,

        /* A dependency created because of some unit's RequiresMountsFor= setting */
        UNIT_DEPENDENCY_PATH               = 1 << 4,

        /* A dependency created because of data read from /proc/self/mountinfo and no other configuration source */
        UNIT_DEPENDENCY_MOUNTINFO_IMPLICIT = 1 << 5,

        /* A dependency created because of data read from /proc/self/mountinfo, but conditionalized by
         * DefaultDependencies= and thus also involving configuration from UNIT_DEPENDENCY_FILE sources */
        UNIT_DEPENDENCY_MOUNTINFO_DEFAULT  = 1 << 6,

        /* A dependency created because of data read from /proc/swaps and no other configuration source */
        UNIT_DEPENDENCY_PROC_SWAP          = 1 << 7,

        /* A dependency for units in slices assigned by directly setting Slice= */
        UNIT_DEPENDENCY_SLICE_PROPERTY     = 1 << 8,

        _UNIT_DEPENDENCY_MASK_FULL         = (1 << 9) - 1,
} UnitDependencyMask;

/* The Unit's dependencies[] hashmaps use this structure as value. It has the same size as a void pointer, and thus can
 * be stored directly as hashmap value, without any indirection. Note that this stores two masks, as both the origin
 * and the destination of a dependency might have created it. */
typedef union UnitDependencyInfo {
        void *data;
        struct {
                UnitDependencyMask origin_mask:16;
                UnitDependencyMask destination_mask:16;
        } _packed_;
} UnitDependencyInfo;

/* Newer LLVM versions don't like implicit casts from large pointer types to smaller enums, hence let's add
 * explicit type-safe helpers for that. */
static inline UnitDependency UNIT_DEPENDENCY_FROM_PTR(const void *p) {
        return PTR_TO_INT(p);
}

static inline void* UNIT_DEPENDENCY_TO_PTR(UnitDependency d) {
        return INT_TO_PTR(d);
}

#include "job.h"

struct UnitRef {
        /* Keeps tracks of references to a unit. This is useful so
         * that we can merge two units if necessary and correct all
         * references to them */

        Unit *source, *target;
        LIST_FIELDS(UnitRef, refs_by_target);
};

typedef struct Unit {
        Manager *manager;

        UnitType type;
        UnitLoadState load_state;
        Unit *merged_into;

        char *id;   /* The one special name that we use for identification */
        char *instance;

        Set *aliases; /* All the other names. */

        /* For each dependency type we can look up another Hashmap with this, whose key is a Unit* object,
         * and whose value encodes why the dependency exists, using the UnitDependencyInfo type. i.e. a
         * Hashmap(UnitDependency → Hashmap(Unit* → UnitDependencyInfo)) */
        Hashmap *dependencies;

        /* Similar, for RequiresMountsFor= path dependencies. The key is the path, the value the
         * UnitDependencyInfo type */
        Hashmap *requires_mounts_for;

        char *description;
        char **documentation;

        char *fragment_path; /* if loaded from a config file this is the primary path to it */
        char *source_path; /* if converted, the source file */
        char **dropin_paths;

        usec_t fragment_not_found_timestamp_hash;
        usec_t fragment_mtime;
        usec_t source_mtime;
        usec_t dropin_mtime;

        /* If this is a transient unit we are currently writing, this is where we are writing it to */
        FILE *transient_file;

        /* Freezer state */
        sd_bus_message *pending_freezer_message;
        FreezerState freezer_state;

        /* Job timeout and action to take */
        EmergencyAction job_timeout_action;
        usec_t job_timeout;
        usec_t job_running_timeout;
        char *job_timeout_reboot_arg;

        /* If there is something to do with this unit, then this is the installed job for it */
        Job *job;

        /* JOB_NOP jobs are special and can be installed without disturbing the real job. */
        Job *nop_job;

        /* The slot used for watching NameOwnerChanged signals */
        sd_bus_slot *match_bus_slot;
        sd_bus_slot *get_name_owner_slot;

        /* References to this unit from clients */
        sd_bus_track *bus_track;
        char **deserialized_refs;

        /* References to this */
        LIST_HEAD(UnitRef, refs_by_target);

        /* Conditions to check */
        LIST_HEAD(Condition, conditions);
        LIST_HEAD(Condition, asserts);

        dual_timestamp condition_timestamp;
        dual_timestamp assert_timestamp;

        /* Updated whenever the low-level state changes */
        dual_timestamp state_change_timestamp;

        /* Updated whenever the (high-level) active state enters or leaves the active or inactive states */
        dual_timestamp inactive_exit_timestamp;
        dual_timestamp active_enter_timestamp;
        dual_timestamp active_exit_timestamp;
        dual_timestamp inactive_enter_timestamp;

        /* Per type list */
        LIST_FIELDS(Unit, units_by_type);

        /* Load queue */
        LIST_FIELDS(Unit, load_queue);

        /* D-Bus queue */
        LIST_FIELDS(Unit, dbus_queue);

        /* Cleanup queue */
        LIST_FIELDS(Unit, cleanup_queue);

        /* GC queue */
        LIST_FIELDS(Unit, gc_queue);

        /* CGroup realize members queue */
        LIST_FIELDS(Unit, cgroup_realize_queue);

        /* cgroup empty queue */
        LIST_FIELDS(Unit, cgroup_empty_queue);

        /* cgroup OOM queue */
        LIST_FIELDS(Unit, cgroup_oom_queue);

        /* Target dependencies queue */
        LIST_FIELDS(Unit, target_deps_queue);

        /* Queue of units with StopWhenUnneeded= set that shall be checked for clean-up. */
        LIST_FIELDS(Unit, stop_when_unneeded_queue);

        /* Queue of units that have an Uphold= dependency from some other unit, and should be checked for starting */
        LIST_FIELDS(Unit, start_when_upheld_queue);

        /* Queue of units that have a BindTo= dependency on some other unit, and should possibly be shut down */
        LIST_FIELDS(Unit, stop_when_bound_queue);

        /* PIDs we keep an eye on. Note that a unit might have many
         * more, but these are the ones we care enough about to
         * process SIGCHLD for */
        Set *pids;

        /* Used in SIGCHLD and sd_notify() message event invocation logic to avoid that we dispatch the same event
         * multiple times on the same unit. */
        unsigned sigchldgen;
        unsigned notifygen;

        /* Used during GC sweeps */
        unsigned gc_marker;

        /* Error code when we didn't manage to load the unit (negative) */
        int load_error;

        /* Put a ratelimit on unit starting */
        RateLimit start_ratelimit;
        EmergencyAction start_limit_action;

        /* The unit has been marked for reload, restart, etc. Stored as 1u << marker1 | 1u << marker2. */
        unsigned markers;

        /* What to do on failure or success */
        EmergencyAction success_action, failure_action;
        int success_action_exit_status, failure_action_exit_status;
        char *reboot_arg;

        /* Make sure we never enter endless loops with the StopWhenUnneeded=, BindsTo=, Uphold= logic */
        RateLimit auto_start_stop_ratelimit;

        /* Reference to a specific UID/GID */
        uid_t ref_uid;
        gid_t ref_gid;

        /* Cached unit file state and preset */
        UnitFileState unit_file_state;
        int unit_file_preset;

        /* Where the cpu.stat or cpuacct.usage was at the time the unit was started */
        nsec_t cpu_usage_base;
        nsec_t cpu_usage_last; /* the most recently read value */

        /* The current counter of processes sent SIGKILL by systemd-oomd */
        uint64_t managed_oom_kill_last;

        /* The current counter of the oom_kill field in the memory.events cgroup attribute */
        uint64_t oom_kill_last;

        /* Where the io.stat data was at the time the unit was started */
        uint64_t io_accounting_base[_CGROUP_IO_ACCOUNTING_METRIC_MAX];
        uint64_t io_accounting_last[_CGROUP_IO_ACCOUNTING_METRIC_MAX]; /* the most recently read value */

        /* Counterparts in the cgroup filesystem */
        char *cgroup_path;
        uint64_t cgroup_id;
        CGroupMask cgroup_realized_mask;           /* In which hierarchies does this unit's cgroup exist? (only relevant on cgroup v1) */
        CGroupMask cgroup_enabled_mask;            /* Which controllers are enabled (or more correctly: enabled for the children) for this unit's cgroup? (only relevant on cgroup v2) */
        CGroupMask cgroup_invalidated_mask;        /* A mask specifying controllers which shall be considered invalidated, and require re-realization */
        CGroupMask cgroup_members_mask;            /* A cache for the controllers required by all children of this cgroup (only relevant for slice units) */

        /* Inotify watch descriptors for watching cgroup.events and memory.events on cgroupv2 */
        int cgroup_control_inotify_wd;
        int cgroup_memory_inotify_wd;

        /* Device Controller BPF program */
        BPFProgram *bpf_device_control_installed;

        /* IP BPF Firewalling/accounting */
        int ip_accounting_ingress_map_fd;
        int ip_accounting_egress_map_fd;
        uint64_t ip_accounting_extra[_CGROUP_IP_ACCOUNTING_METRIC_MAX];

        int ipv4_allow_map_fd;
        int ipv6_allow_map_fd;
        int ipv4_deny_map_fd;
        int ipv6_deny_map_fd;
        BPFProgram *ip_bpf_ingress, *ip_bpf_ingress_installed;
        BPFProgram *ip_bpf_egress, *ip_bpf_egress_installed;

        Set *ip_bpf_custom_ingress;
        Set *ip_bpf_custom_ingress_installed;
        Set *ip_bpf_custom_egress;
        Set *ip_bpf_custom_egress_installed;

        /* BPF programs managed (e.g. loaded to kernel) by an entity external to systemd,
         * attached to unit cgroup by provided program fd and attach type. */
        Hashmap *bpf_foreign_by_key;

        FDSet *initial_socket_bind_link_fds;
#if BPF_FRAMEWORK
        /* BPF links to BPF programs attached to cgroup/bind{4|6} hooks and
         * responsible for allowing or denying a unit to bind(2) to a socket
         * address. */
        struct bpf_link *ipv4_socket_bind_link;
        struct bpf_link *ipv6_socket_bind_link;
#endif

        FDSet *initial_restric_ifaces_link_fds;
#if BPF_FRAMEWORK
        struct bpf_link *restrict_ifaces_ingress_bpf_link;
        struct bpf_link *restrict_ifaces_egress_bpf_link;
#endif

        /* Low-priority event source which is used to remove watched PIDs that have gone away, and subscribe to any new
         * ones which might have appeared. */
        sd_event_source *rewatch_pids_event_source;

        /* How to start OnSuccess=/OnFailure= units */
        JobMode on_success_job_mode;
        JobMode on_failure_job_mode;

        /* Tweaking the GC logic */
        CollectMode collect_mode;

        /* The current invocation ID */
        sd_id128_t invocation_id;
        char invocation_id_string[SD_ID128_STRING_MAX]; /* useful when logging */

        /* Garbage collect us we nobody wants or requires us anymore */
        bool stop_when_unneeded;

        /* Create default dependencies */
        bool default_dependencies;

        /* Refuse manual starting, allow starting only indirectly via dependency. */
        bool refuse_manual_start;

        /* Don't allow the user to stop this unit manually, allow stopping only indirectly via dependency. */
        bool refuse_manual_stop;

        /* Allow isolation requests */
        bool allow_isolate;

        /* Ignore this unit when isolating */
        bool ignore_on_isolate;

        /* Did the last condition check succeed? */
        bool condition_result;
        bool assert_result;

        /* Is this a transient unit? */
        bool transient;

        /* Is this a unit that is always running and cannot be stopped? */
        bool perpetual;

        /* Booleans indicating membership of this unit in the various queues */
        bool in_load_queue:1;
        bool in_dbus_queue:1;
        bool in_cleanup_queue:1;
        bool in_gc_queue:1;
        bool in_cgroup_realize_queue:1;
        bool in_cgroup_empty_queue:1;
        bool in_cgroup_oom_queue:1;
        bool in_target_deps_queue:1;
        bool in_stop_when_unneeded_queue:1;
        bool in_start_when_upheld_queue:1;
        bool in_stop_when_bound_queue:1;

        bool sent_dbus_new_signal:1;

        bool job_running_timeout_set:1;

        bool in_audit:1;
        bool on_console:1;

        bool cgroup_realized:1;
        bool cgroup_members_mask_valid:1;

        /* Reset cgroup accounting next time we fork something off */
        bool reset_accounting:1;

        bool start_limit_hit:1;

        /* Did we already invoke unit_coldplug() for this unit? */
        bool coldplugged:1;

        /* For transient units: whether to add a bus track reference after creating the unit */
        bool bus_track_add:1;

        /* Remember which unit state files we created */
        bool exported_invocation_id:1;
        bool exported_log_level_max:1;
        bool exported_log_extra_fields:1;
        bool exported_log_ratelimit_interval:1;
        bool exported_log_ratelimit_burst:1;

        /* Whether we warned about clamping the CPU quota period */
        bool warned_clamping_cpu_quota_period:1;

        /* When writing transient unit files, stores which section we stored last. If < 0, we didn't write any yet. If
         * == 0 we are in the [Unit] section, if > 0 we are in the unit type-specific section. */
        signed int last_section_private:2;
} Unit;

typedef struct UnitStatusMessageFormats {
        const char *starting_stopping[2];
        const char *finished_start_job[_JOB_RESULT_MAX];
        const char *finished_stop_job[_JOB_RESULT_MAX];
        /* If this entry is present, it'll be called to provide a context-dependent format string,
         * or NULL to fall back to finished_{start,stop}_job; if those are NULL too, fall back to generic. */
        const char *(*finished_job)(Unit *u, JobType t, JobResult result);
} UnitStatusMessageFormats;

/* Flags used when writing drop-in files or transient unit files */
typedef enum UnitWriteFlags {
        /* Write a runtime unit file or drop-in (i.e. one below /run) */
        UNIT_RUNTIME           = 1 << 0,

        /* Write a persistent drop-in (i.e. one below /etc) */
        UNIT_PERSISTENT        = 1 << 1,

        /* Place this item in the per-unit-type private section, instead of [Unit] */
        UNIT_PRIVATE           = 1 << 2,

        /* Apply specifier escaping before writing */
        UNIT_ESCAPE_SPECIFIERS = 1 << 3,

        /* Apply C escaping before writing */
        UNIT_ESCAPE_C          = 1 << 4,
} UnitWriteFlags;

/* Returns true if neither persistent, nor runtime storage is requested, i.e. this is a check invocation only */
static inline bool UNIT_WRITE_FLAGS_NOOP(UnitWriteFlags flags) {
        return (flags & (UNIT_RUNTIME|UNIT_PERSISTENT)) == 0;
}

#include "kill.h"

typedef struct UnitVTable {
        /* How much memory does an object of this unit type need */
        size_t object_size;

        /* If greater than 0, the offset into the object where
         * ExecContext is found, if the unit type has that */
        size_t exec_context_offset;

        /* If greater than 0, the offset into the object where
         * CGroupContext is found, if the unit type has that */
        size_t cgroup_context_offset;

        /* If greater than 0, the offset into the object where
         * KillContext is found, if the unit type has that */
        size_t kill_context_offset;

        /* If greater than 0, the offset into the object where the
         * pointer to ExecRuntime is found, if the unit type has
         * that */
        size_t exec_runtime_offset;

        /* If greater than 0, the offset into the object where the pointer to DynamicCreds is found, if the unit type
         * has that. */
        size_t dynamic_creds_offset;

        /* The name of the configuration file section with the private settings of this unit */
        const char *private_section;

        /* Config file sections this unit type understands, separated
         * by NUL chars */
        const char *sections;

        /* This should reset all type-specific variables. This should
         * not allocate memory, and is called with zero-initialized
         * data. It should hence only initialize variables that need
         * to be set != 0. */
        void (*init)(Unit *u);

        /* This should free all type-specific variables. It should be
         * idempotent. */
        void (*done)(Unit *u);

        /* Actually load data from disk. This may fail, and should set
         * load_state to UNIT_LOADED, UNIT_MERGED or leave it at
         * UNIT_STUB if no configuration could be found. */
        int (*load)(Unit *u);

        /* During deserialization we only record the intended state to return to. With coldplug() we actually put the
         * deserialized state in effect. This is where unit_notify() should be called to start things up. Note that
         * this callback is invoked *before* we leave the reloading state of the manager, i.e. *before* we consider the
         * reloading to be complete. Thus, this callback should just restore the exact same state for any unit that was
         * in effect before the reload, i.e. units should not catch up with changes happened during the reload. That's
         * what catchup() below is for. */
        int (*coldplug)(Unit *u);

        /* This is called shortly after all units' coldplug() call was invoked, and *after* the manager left the
         * reloading state. It's supposed to catch up with state changes due to external events we missed so far (for
         * example because they took place while we were reloading/reexecing) */
        void (*catchup)(Unit *u);

        void (*dump)(Unit *u, FILE *f, const char *prefix);

        int (*start)(Unit *u);
        int (*stop)(Unit *u);
        int (*reload)(Unit *u);

        int (*kill)(Unit *u, KillWho w, int signo, sd_bus_error *error);

        /* Clear out the various runtime/state/cache/logs/configuration data */
        int (*clean)(Unit *u, ExecCleanMask m);

        /* Freeze the unit */
        int (*freeze)(Unit *u);
        int (*thaw)(Unit *u);
        bool (*can_freeze)(Unit *u);

        /* Return which kind of data can be cleaned */
        int (*can_clean)(Unit *u, ExecCleanMask *ret);

        bool (*can_reload)(Unit *u);

        /* Serialize state and file descriptors that should be carried over into the new
         * instance after reexecution. */
        int (*serialize)(Unit *u, FILE *f, FDSet *fds);

        /* Restore one item from the serialization */
        int (*deserialize_item)(Unit *u, const char *key, const char *data, FDSet *fds);

        /* Try to match up fds with what we need for this unit */
        void (*distribute_fds)(Unit *u, FDSet *fds);

        /* Boils down the more complex internal state of this unit to
         * a simpler one that the engine can understand */
        UnitActiveState (*active_state)(Unit *u);

        /* Returns the substate specific to this unit type as
         * string. This is purely information so that we can give the
         * user a more fine grained explanation in which actual state a
         * unit is in. */
        const char* (*sub_state_to_string)(Unit *u);

        /* Additionally to UnitActiveState determine whether unit is to be restarted. */
        bool (*will_restart)(Unit *u);

        /* Return false when there is a reason to prevent this unit from being gc'ed
         * even though nothing references it and it isn't active in any way. */
        bool (*may_gc)(Unit *u);

        /* Return true when the unit is not controlled by the manager (e.g. extrinsic mounts). */
        bool (*is_extrinsic)(Unit *u);

        /* When the unit is not running and no job for it queued we shall release its runtime resources */
        void (*release_resources)(Unit *u);

        /* Invoked on every child that died */
        void (*sigchld_event)(Unit *u, pid_t pid, int code, int status);

        /* Reset failed state if we are in failed state */
        void (*reset_failed)(Unit *u);

        /* Called whenever any of the cgroups this unit watches for ran empty */
        void (*notify_cgroup_empty)(Unit *u);

        /* Called whenever an OOM kill event on this unit was seen */
        void (*notify_cgroup_oom)(Unit *u);

        /* Called whenever a process of this unit sends us a message */
        void (*notify_message)(Unit *u, const struct ucred *ucred, char * const *tags, FDSet *fds);

        /* Called whenever a name this Unit registered for comes or goes away. */
        void (*bus_name_owner_change)(Unit *u, const char *new_owner);

        /* Called for each property that is being set */
        int (*bus_set_property)(Unit *u, const char *name, sd_bus_message *message, UnitWriteFlags flags, sd_bus_error *error);

        /* Called after at least one property got changed to apply the necessary change */
        int (*bus_commit_properties)(Unit *u);

        /* Return the unit this unit is following */
        Unit *(*following)(Unit *u);

        /* Return the set of units that are following each other */
        int (*following_set)(Unit *u, Set **s);

        /* Invoked each time a unit this unit is triggering changes
         * state or gains/loses a job */
        void (*trigger_notify)(Unit *u, Unit *trigger);

        /* Called whenever CLOCK_REALTIME made a jump */
        void (*time_change)(Unit *u);

        /* Called whenever /etc/localtime was modified */
        void (*timezone_change)(Unit *u);

        /* Returns the next timeout of a unit */
        int (*get_timeout)(Unit *u, usec_t *timeout);

        /* Returns the main PID if there is any defined, or 0. */
        pid_t (*main_pid)(Unit *u);

        /* Returns the main PID if there is any defined, or 0. */
        pid_t (*control_pid)(Unit *u);

        /* Returns true if the unit currently needs access to the console */
        bool (*needs_console)(Unit *u);

        /* Returns the exit status to propagate in case of FailureAction=exit/SuccessAction=exit; usually returns the
         * exit code of the "main" process of the service or similar. */
        int (*exit_status)(Unit *u);

        /* Return a copy of the status string pointer. */
        const char* (*status_text)(Unit *u);

        /* Like the enumerate() callback further down, but only enumerates the perpetual units, i.e. all units that
         * unconditionally exist and are always active. The main reason to keep both enumeration functions separate is
         * philosophical: the state of perpetual units should be put in place by coldplug(), while the state of those
         * discovered through regular enumeration should be put in place by catchup(), see below. */
        void (*enumerate_perpetual)(Manager *m);

        /* This is called for each unit type and should be used to enumerate units already existing in the system
         * internally and load them. However, everything that is loaded here should still stay in inactive state. It is
         * the job of the catchup() call above to put the units into the discovered state. */
        void (*enumerate)(Manager *m);

        /* Type specific cleanups. */
        void (*shutdown)(Manager *m);

        /* If this function is set and returns false all jobs for units
         * of this type will immediately fail. */
        bool (*supported)(void);

        /* If this function is set, it's invoked first as part of starting a unit to allow start rate
         * limiting checks to occur before we do anything else. */
        int (*can_start)(Unit *u);

        /* The strings to print in status messages */
        UnitStatusMessageFormats status_message_formats;

        /* True if transient units of this type are OK */
        bool can_transient;

        /* True if cgroup delegation is permissible */
        bool can_delegate;

        /* True if the unit type triggers other units, i.e. can have a UNIT_TRIGGERS dependency */
        bool can_trigger;

        /* True if the unit type knows a failure state, and thus can be source of an OnFailure= dependency */
        bool can_fail;

        /* True if units of this type shall be startable only once and then never again */
        bool once_only;

        /* Do not serialize this unit when preparing for root switch */
        bool exclude_from_switch_root_serialization;

        /* True if queued jobs of this type should be GC'ed if no other job needs them anymore */
        bool gc_jobs;

        /* True if systemd-oomd can monitor and act on this unit's recursive children's cgroup(s)  */
        bool can_set_managed_oom;
} UnitVTable;

extern const UnitVTable * const unit_vtable[_UNIT_TYPE_MAX];

static inline const UnitVTable* UNIT_VTABLE(const Unit *u) {
        return unit_vtable[u->type];
}

/* For casting a unit into the various unit types */
#define DEFINE_CAST(UPPERCASE, MixedCase)                               \
        static inline MixedCase* UPPERCASE(Unit *u) {                   \
                if (_unlikely_(!u || u->type != UNIT_##UPPERCASE))      \
                        return NULL;                                    \
                                                                        \
                return (MixedCase*) u;                                  \
        }

/* For casting the various unit types into a unit */
#define UNIT(u)                                         \
        ({                                              \
                typeof(u) _u_ = (u);                    \
                Unit *_w_ = _u_ ? &(_u_)->meta : NULL;  \
                _w_;                                    \
        })

#define UNIT_HAS_EXEC_CONTEXT(u) (UNIT_VTABLE(u)->exec_context_offset > 0)
#define UNIT_HAS_CGROUP_CONTEXT(u) (UNIT_VTABLE(u)->cgroup_context_offset > 0)
#define UNIT_HAS_KILL_CONTEXT(u) (UNIT_VTABLE(u)->kill_context_offset > 0)

Unit* unit_has_dependency(const Unit *u, UnitDependencyAtom atom, Unit *other);
int unit_get_dependency_array(const Unit *u, UnitDependencyAtom atom, Unit ***ret_array);

static inline Hashmap* unit_get_dependencies(Unit *u, UnitDependency d) {
        return hashmap_get(u->dependencies, UNIT_DEPENDENCY_TO_PTR(d));
}

static inline Unit* UNIT_TRIGGER(Unit *u) {
        return unit_has_dependency(u, UNIT_ATOM_TRIGGERS, NULL);
}

static inline Unit* UNIT_GET_SLICE(const Unit *u) {
        return unit_has_dependency(u, UNIT_ATOM_IN_SLICE, NULL);
}

Unit* unit_new(Manager *m, size_t size);
Unit* unit_free(Unit *u);
DEFINE_TRIVIAL_CLEANUP_FUNC(Unit *, unit_free);

int unit_new_for_name(Manager *m, size_t size, const char *name, Unit **ret);
int unit_add_name(Unit *u, const char *name);

int unit_add_dependency(Unit *u, UnitDependency d, Unit *other, bool add_reference, UnitDependencyMask mask);
int unit_add_two_dependencies(Unit *u, UnitDependency d, UnitDependency e, Unit *other, bool add_reference, UnitDependencyMask mask);

int unit_add_dependency_by_name(Unit *u, UnitDependency d, const char *name, bool add_reference, UnitDependencyMask mask);
int unit_add_two_dependencies_by_name(Unit *u, UnitDependency d, UnitDependency e, const char *name, bool add_reference, UnitDependencyMask mask);

int unit_add_exec_dependencies(Unit *u, ExecContext *c);

int unit_choose_id(Unit *u, const char *name);
int unit_set_description(Unit *u, const char *description);

bool unit_may_gc(Unit *u);

static inline bool unit_is_extrinsic(Unit *u) {
        return u->perpetual ||
                (UNIT_VTABLE(u)->is_extrinsic && UNIT_VTABLE(u)->is_extrinsic(u));
}

static inline const char* unit_status_text(Unit *u) {
        if (u && UNIT_VTABLE(u)->status_text)
                return UNIT_VTABLE(u)->status_text(u);
        return NULL;
}

void unit_add_to_load_queue(Unit *u);
void unit_add_to_dbus_queue(Unit *u);
void unit_add_to_cleanup_queue(Unit *u);
void unit_add_to_gc_queue(Unit *u);
void unit_add_to_target_deps_queue(Unit *u);
void unit_submit_to_stop_when_unneeded_queue(Unit *u);
void unit_submit_to_start_when_upheld_queue(Unit *u);
void unit_submit_to_stop_when_bound_queue(Unit *u);

int unit_merge(Unit *u, Unit *other);
int unit_merge_by_name(Unit *u, const char *other);

Unit *unit_follow_merge(Unit *u) _pure_;

int unit_load_fragment_and_dropin(Unit *u, bool fragment_required);
int unit_load(Unit *unit);

int unit_set_slice(Unit *u, Unit *slice);
int unit_set_default_slice(Unit *u);

const char *unit_description(Unit *u) _pure_;
const char *unit_status_string(Unit *u, char **combined);

bool unit_has_name(const Unit *u, const char *name);

UnitActiveState unit_active_state(Unit *u);
FreezerState unit_freezer_state(Unit *u);
int unit_freezer_state_kernel(Unit *u, FreezerState *ret);

const char* unit_sub_state_to_string(Unit *u);

bool unit_can_reload(Unit *u) _pure_;
bool unit_can_start(Unit *u) _pure_;
bool unit_can_stop(Unit *u) _pure_;
bool unit_can_isolate(Unit *u) _pure_;

int unit_start(Unit *u);
int unit_stop(Unit *u);
int unit_reload(Unit *u);

int unit_kill(Unit *u, KillWho w, int signo, sd_bus_error *error);
int unit_kill_common(Unit *u, KillWho who, int signo, pid_t main_pid, pid_t control_pid, sd_bus_error *error);

typedef enum UnitNotifyFlags {
        UNIT_NOTIFY_RELOAD_FAILURE    = 1 << 0,
        UNIT_NOTIFY_WILL_AUTO_RESTART = 1 << 1,
} UnitNotifyFlags;

void unit_notify(Unit *u, UnitActiveState os, UnitActiveState ns, UnitNotifyFlags flags);

int unit_watch_pid(Unit *u, pid_t pid, bool exclusive);
void unit_unwatch_pid(Unit *u, pid_t pid);
void unit_unwatch_all_pids(Unit *u);

int unit_enqueue_rewatch_pids(Unit *u);
void unit_dequeue_rewatch_pids(Unit *u);

int unit_install_bus_match(Unit *u, sd_bus *bus, const char *name);
int unit_watch_bus_name(Unit *u, const char *name);
void unit_unwatch_bus_name(Unit *u, const char *name);

bool unit_job_is_applicable(Unit *u, JobType j);

int set_unit_path(const char *p);

char *unit_dbus_path(Unit *u);
char *unit_dbus_path_invocation_id(Unit *u);

int unit_load_related_unit(Unit *u, const char *type, Unit **_found);

int unit_add_node_dependency(Unit *u, const char *what, UnitDependency d, UnitDependencyMask mask);
int unit_add_blockdev_dependency(Unit *u, const char *what, UnitDependencyMask mask);

int unit_coldplug(Unit *u);
void unit_catchup(Unit *u);

void unit_status_printf(Unit *u, StatusType status_type, const char *status, const char *format, const char *ident) _printf_(4, 0);

bool unit_need_daemon_reload(Unit *u);

void unit_reset_failed(Unit *u);

Unit *unit_following(Unit *u);
int unit_following_set(Unit *u, Set **s);

const char *unit_slice_name(Unit *u);

bool unit_stop_pending(Unit *u) _pure_;
bool unit_inactive_or_pending(Unit *u) _pure_;
bool unit_active_or_pending(Unit *u);
bool unit_will_restart_default(Unit *u);
bool unit_will_restart(Unit *u);

int unit_add_default_target_dependency(Unit *u, Unit *target);

void unit_start_on_failure(Unit *u, const char *dependency_name, UnitDependencyAtom atom, JobMode job_mode);
void unit_trigger_notify(Unit *u);

UnitFileState unit_get_unit_file_state(Unit *u);
int unit_get_unit_file_preset(Unit *u);

Unit* unit_ref_set(UnitRef *ref, Unit *source, Unit *target);
void unit_ref_unset(UnitRef *ref);

#define UNIT_DEREF(ref) ((ref).target)
#define UNIT_ISSET(ref) (!!(ref).target)

int unit_patch_contexts(Unit *u);

ExecContext *unit_get_exec_context(const Unit *u) _pure_;
KillContext *unit_get_kill_context(Unit *u) _pure_;
CGroupContext *unit_get_cgroup_context(Unit *u) _pure_;

ExecRuntime *unit_get_exec_runtime(Unit *u) _pure_;

int unit_setup_exec_runtime(Unit *u);
int unit_setup_dynamic_creds(Unit *u);

char* unit_escape_setting(const char *s, UnitWriteFlags flags, char **buf);
char* unit_concat_strv(char **l, UnitWriteFlags flags);

int unit_write_setting(Unit *u, UnitWriteFlags flags, const char *name, const char *data);
int unit_write_settingf(Unit *u, UnitWriteFlags mode, const char *name, const char *format, ...) _printf_(4,5);

int unit_kill_context(Unit *u, KillContext *c, KillOperation k, pid_t main_pid, pid_t control_pid, bool main_pid_alien);

int unit_make_transient(Unit *u);

int unit_require_mounts_for(Unit *u, const char *path, UnitDependencyMask mask);

bool unit_type_supported(UnitType t);

bool unit_is_pristine(Unit *u);

bool unit_is_unneeded(Unit *u);
bool unit_is_upheld_by_active(Unit *u, Unit **ret_culprit);
bool unit_is_bound_by_inactive(Unit *u, Unit **ret_culprit);

pid_t unit_control_pid(Unit *u);
pid_t unit_main_pid(Unit *u);

void unit_warn_if_dir_nonempty(Unit *u, const char* where);
int unit_fail_if_noncanonical(Unit *u, const char* where);

int unit_test_start_limit(Unit *u);

int unit_ref_uid_gid(Unit *u, uid_t uid, gid_t gid);
void unit_unref_uid_gid(Unit *u, bool destroy_now);

void unit_notify_user_lookup(Unit *u, uid_t uid, gid_t gid);

int unit_set_invocation_id(Unit *u, sd_id128_t id);
int unit_acquire_invocation_id(Unit *u);

bool unit_shall_confirm_spawn(Unit *u);

int unit_set_exec_params(Unit *s, ExecParameters *p);

int unit_fork_helper_process(Unit *u, const char *name, pid_t *ret);
int unit_fork_and_watch_rm_rf(Unit *u, char **paths, pid_t *ret_pid);

void unit_remove_dependencies(Unit *u, UnitDependencyMask mask);

void unit_export_state_files(Unit *u);
void unit_unlink_state_files(Unit *u);

int unit_prepare_exec(Unit *u);

int unit_log_leftover_process_start(pid_t pid, int sig, void *userdata);
int unit_log_leftover_process_stop(pid_t pid, int sig, void *userdata);
int unit_warn_leftover_processes(Unit *u, cg_kill_log_func_t log_func);

bool unit_needs_console(Unit *u);

const char *unit_label_path(const Unit *u);

int unit_pid_attachable(Unit *unit, pid_t pid, sd_bus_error *error);

static inline bool unit_has_job_type(Unit *u, JobType type) {
        return u && u->job && u->job->type == type;
}

static inline bool unit_log_level_test(const Unit *u, int level) {
        ExecContext *ec = unit_get_exec_context(u);
        return !ec || ec->log_level_max < 0 || ec->log_level_max >= LOG_PRI(level);
}

/* unit_log_skip is for cases like ExecCondition= where a unit is considered "done"
 * after some execution, rather than succeeded or failed. */
void unit_log_skip(Unit *u, const char *result);
void unit_log_success(Unit *u);
void unit_log_failure(Unit *u, const char *result);
static inline void unit_log_result(Unit *u, bool success, const char *result) {
        if (success)
                unit_log_success(u);
        else
                unit_log_failure(u, result);
}

void unit_log_process_exit(Unit *u, const char *kind, const char *command, bool success, int code, int status);

int unit_exit_status(Unit *u);
int unit_success_action_exit_status(Unit *u);
int unit_failure_action_exit_status(Unit *u);

int unit_test_trigger_loaded(Unit *u);

void unit_destroy_runtime_data(Unit *u, const ExecContext *context);
int unit_clean(Unit *u, ExecCleanMask mask);
int unit_can_clean(Unit *u, ExecCleanMask *ret_mask);

bool unit_can_freeze(Unit *u);
int unit_freeze(Unit *u);
void unit_frozen(Unit *u);

int unit_thaw(Unit *u);
void unit_thawed(Unit *u);

int unit_freeze_vtable_common(Unit *u);
int unit_thaw_vtable_common(Unit *u);

Condition *unit_find_failed_condition(Unit *u);

/* Macros which append UNIT= or USER_UNIT= to the message */

#define log_unit_full_errno_zerook(unit, level, error, ...)             \
        ({                                                              \
                const Unit *_u = (unit);                                \
                const int _l = (level);                                 \
                (log_get_max_level() < LOG_PRI(_l) || (_u && !unit_log_level_test(_u, _l))) ? -ERRNO_VALUE(error) : \
                        _u ? log_object_internal(_l, error, PROJECT_FILE, __LINE__, __func__, _u->manager->unit_log_field, _u->id, _u->manager->invocation_log_field, _u->invocation_id_string, ##__VA_ARGS__) : \
                                log_internal(_l, error, PROJECT_FILE, __LINE__, __func__, ##__VA_ARGS__); \
        })

#define log_unit_full_errno(unit, level, error, ...) \
        ({                                                              \
                int _error = (error);                                   \
                ASSERT_NON_ZERO(_error);                                \
                log_unit_full_errno_zerook(unit, level, _error, ##__VA_ARGS__); \
        })

#define log_unit_full(unit, level, ...) (void) log_unit_full_errno_zerook(unit, level, 0, __VA_ARGS__)

#define log_unit_debug(unit, ...)   log_unit_full(unit, LOG_DEBUG, __VA_ARGS__)
#define log_unit_info(unit, ...)    log_unit_full(unit, LOG_INFO, __VA_ARGS__)
#define log_unit_notice(unit, ...)  log_unit_full(unit, LOG_NOTICE, __VA_ARGS__)
#define log_unit_warning(unit, ...) log_unit_full(unit, LOG_WARNING, __VA_ARGS__)
#define log_unit_error(unit, ...)   log_unit_full(unit, LOG_ERR, __VA_ARGS__)

#define log_unit_debug_errno(unit, error, ...)   log_unit_full_errno(unit, LOG_DEBUG, error, __VA_ARGS__)
#define log_unit_info_errno(unit, error, ...)    log_unit_full_errno(unit, LOG_INFO, error, __VA_ARGS__)
#define log_unit_notice_errno(unit, error, ...)  log_unit_full_errno(unit, LOG_NOTICE, error, __VA_ARGS__)
#define log_unit_warning_errno(unit, error, ...) log_unit_full_errno(unit, LOG_WARNING, error, __VA_ARGS__)
#define log_unit_error_errno(unit, error, ...)   log_unit_full_errno(unit, LOG_ERR, error, __VA_ARGS__)

#define log_unit_struct_errno(unit, level, error, ...)                  \
        ({                                                              \
                const Unit *_u = (unit);                                \
                const int _l = (level);                                 \
                unit_log_level_test(_u, _l) ?                           \
                        log_struct_errno(_l, error, __VA_ARGS__, LOG_UNIT_ID(_u)) : \
                        -ERRNO_VALUE(error);                            \
        })

#define log_unit_struct(unit, level, ...) log_unit_struct_errno(unit, level, 0, __VA_ARGS__)

#define log_unit_struct_iovec_errno(unit, level, error, iovec, n_iovec) \
        ({                                                              \
                const int _l = (level);                                 \
                unit_log_level_test(unit, _l) ?                         \
                        log_struct_iovec_errno(_l, error, iovec, n_iovec) : \
                        -ERRNO_VALUE(error);                            \
        })

#define log_unit_struct_iovec(unit, level, iovec, n_iovec) log_unit_struct_iovec_errno(unit, level, 0, iovec, n_iovec)

#define LOG_UNIT_MESSAGE(unit, fmt, ...) "MESSAGE=%s: " fmt, (unit)->id, ##__VA_ARGS__
#define LOG_UNIT_ID(unit) (unit)->manager->unit_log_format_string, (unit)->id
#define LOG_UNIT_INVOCATION_ID(unit) (unit)->manager->invocation_log_format_string, (unit)->invocation_id_string

const char* collect_mode_to_string(CollectMode m) _const_;
CollectMode collect_mode_from_string(const char *s) _pure_;

typedef struct UnitForEachDependencyData {
        /* Stores state for the FOREACH macro below for iterating through all deps that have any of the
         * specified dependency atom bits set */
        UnitDependencyAtom match_atom;
        Hashmap *by_type, *by_unit;
        void *current_type;
        Iterator by_type_iterator, by_unit_iterator;
        Unit **current_unit;
} UnitForEachDependencyData;

/* Iterates through all dependencies that have a specific atom in the dependency type set. This tries to be
 * smart: if the atom is unique, we'll directly go to right entry. Otherwise we'll iterate through the
 * per-dependency type hashmap and match all dep that have the right atom set. */
#define _UNIT_FOREACH_DEPENDENCY(other, u, ma, data)                    \
        for (UnitForEachDependencyData data = {                         \
                        .match_atom = (ma),                             \
                        .by_type = (u)->dependencies,                   \
                        .by_type_iterator = ITERATOR_FIRST,             \
                        .current_unit = &(other),                       \
                };                                                      \
             ({                                                         \
                     UnitDependency _dt = _UNIT_DEPENDENCY_INVALID;     \
                     bool _found;                                       \
                                                                        \
                     if (data.by_type && ITERATOR_IS_FIRST(data.by_type_iterator)) { \
                             _dt = unit_dependency_from_unique_atom(data.match_atom); \
                             if (_dt >= 0) {                            \
                                     data.by_unit = hashmap_get(data.by_type, UNIT_DEPENDENCY_TO_PTR(_dt)); \
                                     data.current_type = UNIT_DEPENDENCY_TO_PTR(_dt); \
                                     data.by_type = NULL;               \
                                     _found = !!data.by_unit;           \
                             }                                          \
                     }                                                  \
                     if (_dt < 0)                                       \
                             _found = hashmap_iterate(data.by_type,     \
                                                      &data.by_type_iterator, \
                                                      (void**)&(data.by_unit), \
                                                      (const void**) &(data.current_type)); \
                     _found;                                            \
             }); )                                                      \
                if ((unit_dependency_to_atom(UNIT_DEPENDENCY_FROM_PTR(data.current_type)) & data.match_atom) != 0) \
                        for (data.by_unit_iterator = ITERATOR_FIRST;    \
                                hashmap_iterate(data.by_unit,           \
                                                &data.by_unit_iterator, \
                                                NULL,                   \
                                                (const void**) data.current_unit); )

/* Note: this matches deps that have *any* of the atoms specified in match_atom set */
#define UNIT_FOREACH_DEPENDENCY(other, u, match_atom) \
        _UNIT_FOREACH_DEPENDENCY(other, u, match_atom, UNIQ_T(data, UNIQ))
