transaction: do not add installed jobs to the transaction

[thirdparty/systemd.git] / src / core / transaction.c

#include "transaction.h"
#include "bus-errors.h"

static void transaction_unlink_job(Transaction *tr, Job *j, bool delete_dependencies);

static void transaction_delete_job(Transaction *tr, Job *j, bool delete_dependencies) {
        assert(tr);
        assert(j);

        /* Deletes one job from the transaction */

        transaction_unlink_job(tr, j, delete_dependencies);

        if (!j->installed)
                job_free(j);
}

static void transaction_delete_unit(Transaction *tr, Unit *u) {
        Job *j;

        /* Deletes all jobs associated with a certain unit from the
         * transaction */

        while ((j = hashmap_get(tr->jobs, u)))
                transaction_delete_job(tr, j, true);
}

void transaction_abort(Transaction *tr) {
        Job *j;

        assert(tr);

        while ((j = hashmap_first(tr->jobs)))
                transaction_delete_job(tr, j, true);

        assert(hashmap_isempty(tr->jobs));

        assert(!tr->anchor);
}

static void transaction_find_jobs_that_matter_to_anchor(Transaction *tr, Job *j, unsigned generation) {
        JobDependency *l;

        assert(tr);

        /* A recursive sweep through the graph that marks all units
         * that matter to the anchor job, i.e. are directly or
         * indirectly a dependency of the anchor job via paths that
         * are fully marked as mattering. */

        if (j)
                l = j->subject_list;
        else
                l = tr->anchor;

        LIST_FOREACH(subject, l, l) {

                /* This link does not matter */
                if (!l->matters)
                        continue;

                /* This unit has already been marked */
                if (l->object->generation == generation)
                        continue;

                l->object->matters_to_anchor = true;
                l->object->generation = generation;

                transaction_find_jobs_that_matter_to_anchor(tr, l->object, generation);
        }
}

static void transaction_merge_and_delete_job(Transaction *tr, Job *j, Job *other, JobType t) {
        JobDependency *l, *last;

        assert(j);
        assert(other);
        assert(j->unit == other->unit);
        assert(!j->installed);

        /* Merges 'other' into 'j' and then deletes 'other'. */

        j->type = t;
        j->state = JOB_WAITING;
        j->override = j->override || other->override;

        j->matters_to_anchor = j->matters_to_anchor || other->matters_to_anchor;

        /* Patch us in as new owner of the JobDependency objects */
        last = NULL;
        LIST_FOREACH(subject, l, other->subject_list) {
                assert(l->subject == other);
                l->subject = j;
                last = l;
        }

        /* Merge both lists */
        if (last) {
                last->subject_next = j->subject_list;
                if (j->subject_list)
                        j->subject_list->subject_prev = last;
                j->subject_list = other->subject_list;
        }

        /* Patch us in as new owner of the JobDependency objects */
        last = NULL;
        LIST_FOREACH(object, l, other->object_list) {
                assert(l->object == other);
                l->object = j;
                last = l;
        }

        /* Merge both lists */
        if (last) {
                last->object_next = j->object_list;
                if (j->object_list)
                        j->object_list->object_prev = last;
                j->object_list = other->object_list;
        }

        /* Kill the other job */
        other->subject_list = NULL;
        other->object_list = NULL;
        transaction_delete_job(tr, other, true);
}

static bool job_is_conflicted_by(Job *j) {
        JobDependency *l;

        assert(j);

        /* Returns true if this job is pulled in by a least one
         * ConflictedBy dependency. */

        LIST_FOREACH(object, l, j->object_list)
                if (l->conflicts)
                        return true;

        return false;
}

static int delete_one_unmergeable_job(Transaction *tr, Job *j) {
        Job *k;

        assert(j);

        /* Tries to delete one item in the linked list
         * j->transaction_next->transaction_next->... that conflicts
         * with another one, in an attempt to make an inconsistent
         * transaction work. */

        /* We rely here on the fact that if a merged with b does not
         * merge with c, either a or b merge with c neither */
        LIST_FOREACH(transaction, j, j)
                LIST_FOREACH(transaction, k, j->transaction_next) {
                        Job *d;

                        /* Is this one mergeable? Then skip it */
                        if (job_type_is_mergeable(j->type, k->type))
                                continue;

                        /* Ok, we found two that conflict, let's see if we can
                         * drop one of them */
                        if (!j->matters_to_anchor && !k->matters_to_anchor) {

                                /* Both jobs don't matter, so let's
                                 * find the one that is smarter to
                                 * remove. Let's think positive and
                                 * rather remove stops then starts --
                                 * except if something is being
                                 * stopped because it is conflicted by
                                 * another unit in which case we
                                 * rather remove the start. */

                                log_debug("Looking at job %s/%s conflicted_by=%s", j->unit->id, job_type_to_string(j->type), yes_no(j->type == JOB_STOP && job_is_conflicted_by(j)));
                                log_debug("Looking at job %s/%s conflicted_by=%s", k->unit->id, job_type_to_string(k->type), yes_no(k->type == JOB_STOP && job_is_conflicted_by(k)));

                                if (j->type == JOB_STOP) {

                                        if (job_is_conflicted_by(j))
                                                d = k;
                                        else
                                                d = j;

                                } else if (k->type == JOB_STOP) {

                                        if (job_is_conflicted_by(k))
                                                d = j;
                                        else
                                                d = k;
                                } else
                                        d = j;

                        } else if (!j->matters_to_anchor)
                                d = j;
                        else if (!k->matters_to_anchor)
                                d = k;
                        else
                                return -ENOEXEC;

                        /* Ok, we can drop one, so let's do so. */
                        log_debug("Fixing conflicting jobs by deleting job %s/%s", d->unit->id, job_type_to_string(d->type));
                        transaction_delete_job(tr, d, true);
                        return 0;
                }

        return -EINVAL;
}

static int transaction_merge_jobs(Transaction *tr, DBusError *e) {
        Job *j;
        Iterator i;
        int r;

        assert(tr);

        /* First step, check whether any of the jobs for one specific
         * task conflict. If so, try to drop one of them. */
        HASHMAP_FOREACH(j, tr->jobs, i) {
                JobType t;
                Job *k;

                t = j->type;
                LIST_FOREACH(transaction, k, j->transaction_next) {
                        if (job_type_merge(&t, k->type) >= 0)
                                continue;

                        /* OK, we could not merge all jobs for this
                         * action. Let's see if we can get rid of one
                         * of them */

                        r = delete_one_unmergeable_job(tr, j);
                        if (r >= 0)
                                /* Ok, we managed to drop one, now
                                 * let's ask our callers to call us
                                 * again after garbage collecting */
                                return -EAGAIN;

                        /* We couldn't merge anything. Failure */
                        dbus_set_error(e, BUS_ERROR_TRANSACTION_JOBS_CONFLICTING, "Transaction contains conflicting jobs '%s' and '%s' for %s. Probably contradicting requirement dependencies configured.",
                                       job_type_to_string(t), job_type_to_string(k->type), k->unit->id);
                        return r;
                }
        }

        /* Second step, merge the jobs. */
        HASHMAP_FOREACH(j, tr->jobs, i) {
                JobType t = j->type;
                Job *k;

                /* Merge all transactions */
                LIST_FOREACH(transaction, k, j->transaction_next)
                        assert_se(job_type_merge(&t, k->type) == 0);

                /* If an active job is mergeable, merge it too */
                if (j->unit->job)
                        job_type_merge(&t, j->unit->job->type); /* Might fail. Which is OK */

                while ((k = j->transaction_next)) {
                        if (j->installed) {
                                transaction_merge_and_delete_job(tr, k, j, t);
                                j = k;
                        } else
                                transaction_merge_and_delete_job(tr, j, k, t);
                }

                if (j->unit->job && !j->installed)
                        transaction_merge_and_delete_job(tr, j, j->unit->job, t);

                assert(!j->transaction_next);
                assert(!j->transaction_prev);
        }

        return 0;
}

static void transaction_drop_redundant(Transaction *tr) {
        bool again;

        assert(tr);

        /* Goes through the transaction and removes all jobs that are
         * a noop */

        do {
                Job *j;
                Iterator i;

                again = false;

                HASHMAP_FOREACH(j, tr->jobs, i) {
                        bool changes_something = false;
                        Job *k;

                        LIST_FOREACH(transaction, k, j) {

                                if (!job_is_anchor(k) &&
                                    (k->installed || job_type_is_redundant(k->type, unit_active_state(k->unit))) &&
                                    (!k->unit->job || !job_type_is_conflicting(k->type, k->unit->job->type)))
                                        continue;

                                changes_something = true;
                                break;
                        }

                        if (changes_something)
                                continue;

                        /* log_debug("Found redundant job %s/%s, dropping.", j->unit->id, job_type_to_string(j->type)); */
                        transaction_delete_job(tr, j, false);
                        again = true;
                        break;
                }

        } while (again);
}

static bool unit_matters_to_anchor(Unit *u, Job *j) {
        assert(u);
        assert(!j->transaction_prev);

        /* Checks whether at least one of the jobs for this unit
         * matters to the anchor. */

        LIST_FOREACH(transaction, j, j)
                if (j->matters_to_anchor)
                        return true;

        return false;
}

static int transaction_verify_order_one(Transaction *tr, Job *j, Job *from, unsigned generation, DBusError *e) {
        Iterator i;
        Unit *u;
        int r;

        assert(tr);
        assert(j);
        assert(!j->transaction_prev);

        /* Does a recursive sweep through the ordering graph, looking
         * for a cycle. If we find cycle we try to break it. */

        /* Have we seen this before? */
        if (j->generation == generation) {
                Job *k, *delete;

                /* If the marker is NULL we have been here already and
                 * decided the job was loop-free from here. Hence
                 * shortcut things and return right-away. */
                if (!j->marker)
                        return 0;

                /* So, the marker is not NULL and we already have been
                 * here. We have a cycle. Let's try to break it. We go
                 * backwards in our path and try to find a suitable
                 * job to remove. We use the marker to find our way
                 * back, since smart how we are we stored our way back
                 * in there. */
                log_warning("Found ordering cycle on %s/%s", j->unit->id, job_type_to_string(j->type));

                delete = NULL;
                for (k = from; k; k = ((k->generation == generation && k->marker != k) ? k->marker : NULL)) {

                        log_info("Walked on cycle path to %s/%s", k->unit->id, job_type_to_string(k->type));

                        if (!delete &&
                            !k->installed &&
                            !unit_matters_to_anchor(k->unit, k)) {
                                /* Ok, we can drop this one, so let's
                                 * do so. */
                                delete = k;
                        }

                        /* Check if this in fact was the beginning of
                         * the cycle */
                        if (k == j)
                                break;
                }


                if (delete) {
                        log_warning("Breaking ordering cycle by deleting job %s/%s", delete->unit->id, job_type_to_string(delete->type));
                        transaction_delete_unit(tr, delete->unit);
                        return -EAGAIN;
                }

                log_error("Unable to break cycle");

                dbus_set_error(e, BUS_ERROR_TRANSACTION_ORDER_IS_CYCLIC, "Transaction order is cyclic. See system logs for details.");
                return -ENOEXEC;
        }

        /* Make the marker point to where we come from, so that we can
         * find our way backwards if we want to break a cycle. We use
         * a special marker for the beginning: we point to
         * ourselves. */
        j->marker = from ? from : j;
        j->generation = generation;

        /* We assume that the the dependencies are bidirectional, and
         * hence can ignore UNIT_AFTER */
        SET_FOREACH(u, j->unit->dependencies[UNIT_BEFORE], i) {
                Job *o;

                /* Is there a job for this unit? */
                o = hashmap_get(tr->jobs, u);
                if (!o) {
                        /* Ok, there is no job for this in the
                         * transaction, but maybe there is already one
                         * running? */
                        o = u->job;
                        if (!o)
                                continue;
                }

                r = transaction_verify_order_one(tr, o, j, generation, e);
                if (r < 0)
                        return r;
        }

        /* Ok, let's backtrack, and remember that this entry is not on
         * our path anymore. */
        j->marker = NULL;

        return 0;
}

static int transaction_verify_order(Transaction *tr, unsigned *generation, DBusError *e) {
        Job *j;
        int r;
        Iterator i;
        unsigned g;

        assert(tr);
        assert(generation);

        /* Check if the ordering graph is cyclic. If it is, try to fix
         * that up by dropping one of the jobs. */

        g = (*generation)++;

        HASHMAP_FOREACH(j, tr->jobs, i)
                if ((r = transaction_verify_order_one(tr, j, NULL, g, e)) < 0)
                        return r;

        return 0;
}

static void transaction_collect_garbage(Transaction *tr) {
        bool again;

        assert(tr);

        /* Drop jobs that are not required by any other job */

        do {
                Iterator i;
                Job *j;

                again = false;

                HASHMAP_FOREACH(j, tr->jobs, i) {
                        if (j->object_list) {
                                /* log_debug("Keeping job %s/%s because of %s/%s", */
                                /*           j->unit->id, job_type_to_string(j->type), */
                                /*           j->object_list->subject ? j->object_list->subject->unit->id : "root", */
                                /*           j->object_list->subject ? job_type_to_string(j->object_list->subject->type) : "root"); */
                                continue;
                        }

                        /* log_debug("Garbage collecting job %s/%s", j->unit->id, job_type_to_string(j->type)); */
                        transaction_delete_job(tr, j, true);
                        again = true;
                        break;
                }

        } while (again);
}

static int transaction_is_destructive(Transaction *tr, DBusError *e) {
        Iterator i;
        Job *j;

        assert(tr);

        /* Checks whether applying this transaction means that
         * existing jobs would be replaced */

        HASHMAP_FOREACH(j, tr->jobs, i) {

                /* Assume merged */
                assert(!j->transaction_prev);
                assert(!j->transaction_next);

                if (j->unit->job &&
                    j->unit->job != j &&
                    !job_type_is_superset(j->type, j->unit->job->type)) {

                        dbus_set_error(e, BUS_ERROR_TRANSACTION_IS_DESTRUCTIVE, "Transaction is destructive.");
                        return -EEXIST;
                }
        }

        return 0;
}

static void transaction_minimize_impact(Transaction *tr) {
        bool again;
        assert(tr);

        /* Drops all unnecessary jobs that reverse already active jobs
         * or that stop a running service. */

        do {
                Job *j;
                Iterator i;

                again = false;

                HASHMAP_FOREACH(j, tr->jobs, i) {
                        LIST_FOREACH(transaction, j, j) {
                                bool stops_running_service, changes_existing_job;

                                /* If it matters, we shouldn't drop it */
                                if (j->matters_to_anchor)
                                        continue;

                                /* Would this stop a running service?
                                 * Would this change an existing job?
                                 * If so, let's drop this entry */

                                stops_running_service =
                                        j->type == JOB_STOP && UNIT_IS_ACTIVE_OR_ACTIVATING(unit_active_state(j->unit));

                                changes_existing_job =
                                        j->unit->job &&
                                        job_type_is_conflicting(j->type, j->unit->job->type);

                                if (!stops_running_service && !changes_existing_job)
                                        continue;

                                if (stops_running_service)
                                        log_debug("%s/%s would stop a running service.", j->unit->id, job_type_to_string(j->type));

                                if (changes_existing_job)
                                        log_debug("%s/%s would change existing job.", j->unit->id, job_type_to_string(j->type));

                                /* Ok, let's get rid of this */
                                log_debug("Deleting %s/%s to minimize impact.", j->unit->id, job_type_to_string(j->type));

                                transaction_delete_job(tr, j, true);
                                again = true;
                                break;
                        }

                        if (again)
                                break;
                }

        } while (again);
}

static int transaction_apply(Transaction *tr, Manager *m, JobMode mode) {
        Iterator i;
        Job *j;
        int r;

        /* Moves the transaction jobs to the set of active jobs */

        if (mode == JOB_ISOLATE) {

                /* When isolating first kill all installed jobs which
                 * aren't part of the new transaction */
        rescan:
                HASHMAP_FOREACH(j, m->jobs, i) {
                        assert(j->installed);

                        if (hashmap_get(tr->jobs, j->unit))
                                continue;

                        /* 'j' itself is safe to remove, but if other jobs
                           are invalidated recursively, our iterator may become
                           invalid and we need to start over. */
                        if (job_finish_and_invalidate(j, JOB_CANCELED) > 0)
                                goto rescan;
                }
        }

        HASHMAP_FOREACH(j, tr->jobs, i) {
                /* Assume merged */
                assert(!j->transaction_prev);
                assert(!j->transaction_next);

                if (j->installed)
                        continue;

                r = hashmap_put(m->jobs, UINT32_TO_PTR(j->id), j);
                if (r < 0)
                        goto rollback;
        }

        while ((j = hashmap_steal_first(tr->jobs))) {
                Job *uj;
                if (j->installed) {
                        /* log_debug("Skipping already installed job %s/%s as %u", j->unit->id, job_type_to_string(j->type), (unsigned) j->id); */
                        continue;
                }

                uj = j->unit->job;
                if (uj) {
                        job_uninstall(uj);
                        job_free(uj);
                }

                j->unit->job = j;
                j->installed = true;
                m->n_installed_jobs ++;

                /* We're fully installed. Now let's free data we don't
                 * need anymore. */

                assert(!j->transaction_next);
                assert(!j->transaction_prev);

                /* Clean the job dependencies */
                transaction_unlink_job(tr, j, false);

                job_add_to_run_queue(j);
                job_add_to_dbus_queue(j);
                job_start_timer(j);

                log_debug("Installed new job %s/%s as %u", j->unit->id, job_type_to_string(j->type), (unsigned) j->id);
        }

        assert(!tr->anchor);

        return 0;

rollback:

        HASHMAP_FOREACH(j, tr->jobs, i) {
                if (j->installed)
                        continue;

                hashmap_remove(m->jobs, UINT32_TO_PTR(j->id));
        }

        return r;
}

int transaction_activate(Transaction *tr, Manager *m, JobMode mode, DBusError *e) {
        int r;
        unsigned generation = 1;

        assert(tr);

        /* This applies the changes recorded in tr->jobs to
         * the actual list of jobs, if possible. */

        /* First step: figure out which jobs matter */
        transaction_find_jobs_that_matter_to_anchor(tr, NULL, generation++);

        /* Second step: Try not to stop any running services if
         * we don't have to. Don't try to reverse running
         * jobs if we don't have to. */
        if (mode == JOB_FAIL)
                transaction_minimize_impact(tr);

        /* Third step: Drop redundant jobs */
        transaction_drop_redundant(tr);

        for (;;) {
                /* Fourth step: Let's remove unneeded jobs that might
                 * be lurking. */
                if (mode != JOB_ISOLATE)
                        transaction_collect_garbage(tr);

                /* Fifth step: verify order makes sense and correct
                 * cycles if necessary and possible */
                r = transaction_verify_order(tr, &generation, e);
                if (r >= 0)
                        break;

                if (r != -EAGAIN) {
                        log_warning("Requested transaction contains an unfixable cyclic ordering dependency: %s", bus_error(e, r));
                        return r;
                }

                /* Let's see if the resulting transaction ordering
                 * graph is still cyclic... */
        }

        for (;;) {
                /* Sixth step: let's drop unmergeable entries if
                 * necessary and possible, merge entries we can
                 * merge */
                r = transaction_merge_jobs(tr, e);
                if (r >= 0)
                        break;

                if (r != -EAGAIN) {
                        log_warning("Requested transaction contains unmergeable jobs: %s", bus_error(e, r));
                        return r;
                }

                /* Seventh step: an entry got dropped, let's garbage
                 * collect its dependencies. */
                if (mode != JOB_ISOLATE)
                        transaction_collect_garbage(tr);

                /* Let's see if the resulting transaction still has
                 * unmergeable entries ... */
        }

        /* Eights step: Drop redundant jobs again, if the merging now allows us to drop more. */
        transaction_drop_redundant(tr);

        /* Ninth step: check whether we can actually apply this */
        if (mode == JOB_FAIL) {
                r = transaction_is_destructive(tr, e);
                if (r < 0) {
                        log_notice("Requested transaction contradicts existing jobs: %s", bus_error(e, r));
                        return r;
                }
        }

        /* Tenth step: apply changes */
        r = transaction_apply(tr, m, mode);
        if (r < 0) {
                log_warning("Failed to apply transaction: %s", strerror(-r));
                return r;
        }

        assert(hashmap_isempty(tr->jobs));
        assert(!tr->anchor);

        return 0;
}

static Job* transaction_add_one_job(Transaction *tr, JobType type, Unit *unit, bool override, bool *is_new) {
        Job *j, *f;

        assert(tr);
        assert(unit);

        /* Looks for an existing prospective job and returns that. If
         * it doesn't exist it is created and added to the prospective
         * jobs list. */

        f = hashmap_get(tr->jobs, unit);

        LIST_FOREACH(transaction, j, f) {
                assert(j->unit == unit);

                if (j->type == type) {
                        if (is_new)
                                *is_new = false;
                        return j;
                }
        }

        j = job_new(unit, type);
        if (!j)
                return NULL;

        j->generation = 0;
        j->marker = NULL;
        j->matters_to_anchor = false;
        j->override = override;

        LIST_PREPEND(Job, transaction, f, j);

        if (hashmap_replace(tr->jobs, unit, f) < 0) {
                LIST_REMOVE(Job, transaction, f, j);
                job_free(j);
                return NULL;
        }

        if (is_new)
                *is_new = true;

        /* log_debug("Added job %s/%s to transaction.", unit->id, job_type_to_string(type)); */

        return j;
}

static void transaction_job_dependency_free(Transaction *tr, JobDependency *l) {
        if (!l->subject)
                LIST_REMOVE(JobDependency, subject, tr->anchor, l);
        job_dependency_free(l);
}

static void transaction_unlink_job(Transaction *tr, Job *j, bool delete_dependencies) {
        assert(tr);
        assert(j);

        if (j->transaction_prev)
                j->transaction_prev->transaction_next = j->transaction_next;
        else if (j->transaction_next)
                hashmap_replace(tr->jobs, j->unit, j->transaction_next);
        else
                hashmap_remove_value(tr->jobs, j->unit, j);

        if (j->transaction_next)
                j->transaction_next->transaction_prev = j->transaction_prev;

        j->transaction_prev = j->transaction_next = NULL;

        while (j->subject_list)
                transaction_job_dependency_free(tr, j->subject_list);

        while (j->object_list) {
                Job *other = j->object_list->matters ? j->object_list->subject : NULL;

                transaction_job_dependency_free(tr, j->object_list);

                if (other && delete_dependencies) {
                        log_debug("Deleting job %s/%s as dependency of job %s/%s",
                                  other->unit->id, job_type_to_string(other->type),
                                  j->unit->id, job_type_to_string(j->type));
                        transaction_delete_job(tr, other, delete_dependencies);
                }
        }
}

int transaction_add_job_and_dependencies(
                Transaction *tr,
                JobType type,
                Unit *unit,
                Job *by,
                bool matters,
                bool override,
                bool conflicts,
                bool ignore_requirements,
                bool ignore_order,
                DBusError *e,
                Job **_ret) {
        Job *ret;
        JobDependency *l;
        Iterator i;
        Unit *dep;
        int r;
        bool is_new;

        assert(tr);
        assert(type < _JOB_TYPE_MAX);
        assert(unit);

        /* log_debug("Pulling in %s/%s from %s/%s", */
        /*           unit->id, job_type_to_string(type), */
        /*           by ? by->unit->id : "NA", */
        /*           by ? job_type_to_string(by->type) : "NA"); */

        if (unit->load_state != UNIT_LOADED &&
            unit->load_state != UNIT_ERROR &&
            unit->load_state != UNIT_MASKED) {
                dbus_set_error(e, BUS_ERROR_LOAD_FAILED, "Unit %s is not loaded properly.", unit->id);
                return -EINVAL;
        }

        if (type != JOB_STOP && unit->load_state == UNIT_ERROR) {
                dbus_set_error(e, BUS_ERROR_LOAD_FAILED,
                               "Unit %s failed to load: %s. "
                               "See system logs and 'systemctl status %s' for details.",
                               unit->id,
                               strerror(-unit->load_error),
                               unit->id);
                return -EINVAL;
        }

        if (type != JOB_STOP && unit->load_state == UNIT_MASKED) {
                dbus_set_error(e, BUS_ERROR_MASKED, "Unit %s is masked.", unit->id);
                return -EINVAL;
        }

        if (!unit_job_is_applicable(unit, type)) {
                dbus_set_error(e, BUS_ERROR_JOB_TYPE_NOT_APPLICABLE, "Job type %s is not applicable for unit %s.", job_type_to_string(type), unit->id);
                return -EBADR;
        }

        /* First add the job. */
        ret = transaction_add_one_job(tr, type, unit, override, &is_new);
        if (!ret)
                return -ENOMEM;

        ret->ignore_order = ret->ignore_order || ignore_order;

        /* Then, add a link to the job. */
        l = job_dependency_new(by, ret, matters, conflicts);
        if (!l)
                return -ENOMEM;

        /* If the link has no subject job, it's the anchor link. */
        if (!by)
                LIST_PREPEND(JobDependency, subject, tr->anchor, l);

        if (is_new && !ignore_requirements) {
                Set *following;

                /* If we are following some other unit, make sure we
                 * add all dependencies of everybody following. */
                if (unit_following_set(ret->unit, &following) > 0) {
                        SET_FOREACH(dep, following, i) {
                                r = transaction_add_job_and_dependencies(tr, type, dep, ret, false, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        set_free(following);
                }

                /* Finally, recursively add in all dependencies. */
                if (type == JOB_START || type == JOB_RELOAD_OR_START) {
                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUIRES], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, true, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_BIND_TO], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, true, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUIRES_OVERRIDABLE], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, !override, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_WANTS], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_START, dep, ret, false, false, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUISITE], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_VERIFY_ACTIVE, dep, ret, true, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUISITE_OVERRIDABLE], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_VERIFY_ACTIVE, dep, ret, !override, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_CONFLICTS], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_STOP, dep, ret, true, override, true, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_CONFLICTED_BY], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_STOP, dep, ret, false, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                }

                if (type == JOB_STOP || type == JOB_RESTART || type == JOB_TRY_RESTART) {

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_REQUIRED_BY], i) {
                                r = transaction_add_job_and_dependencies(tr, type, dep, ret, true, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_BOUND_BY], i) {
                                r = transaction_add_job_and_dependencies(tr, type, dep, ret, true, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        if (r != -EBADR)
                                                goto fail;

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }
                }

                if (type == JOB_RELOAD || type == JOB_RELOAD_OR_START) {

                        SET_FOREACH(dep, ret->unit->dependencies[UNIT_PROPAGATE_RELOAD_TO], i) {
                                r = transaction_add_job_and_dependencies(tr, JOB_RELOAD, dep, ret, false, override, false, false, ignore_order, e, NULL);
                                if (r < 0) {
                                        log_warning("Cannot add dependency reload job for unit %s, ignoring: %s", dep->id, bus_error(e, r));

                                        if (e)
                                                dbus_error_free(e);
                                }
                        }
                }

                /* JOB_VERIFY_STARTED, JOB_RELOAD require no dependency handling */
        }

        if (_ret)
                *_ret = ret;

        return 0;

fail:
        return r;
}

int transaction_add_isolate_jobs(Transaction *tr, Manager *m) {
        Iterator i;
        Unit *u;
        char *k;
        int r;

        assert(tr);
        assert(m);

        HASHMAP_FOREACH_KEY(u, k, m->units, i) {

                /* ignore aliases */
                if (u->id != k)
                        continue;

                if (u->ignore_on_isolate)
                        continue;

                /* No need to stop inactive jobs */
                if (UNIT_IS_INACTIVE_OR_FAILED(unit_active_state(u)) && !u->job)
                        continue;

                /* Is there already something listed for this? */
                if (hashmap_get(tr->jobs, u))
                        continue;

                r = transaction_add_job_and_dependencies(tr, JOB_STOP, u, NULL, true, false, false, false, false, NULL, NULL);
                if (r < 0)
                        log_warning("Cannot add isolate job for unit %s, ignoring: %s", u->id, strerror(-r));
        }

        return 0;
}

Transaction *transaction_new(void) {
        Transaction *tr;

        tr = new0(Transaction, 1);
        if (!tr)
                return NULL;

        tr->jobs = hashmap_new(trivial_hash_func, trivial_compare_func);
        if (!tr->jobs) {
                free(tr);
                return NULL;
        }

        return tr;
}

void transaction_free(Transaction *tr) {
        assert(hashmap_isempty(tr->jobs));
        hashmap_free(tr->jobs);
        free(tr);
}