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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation. See file COPYING.
+ *
+ */
+
+#ifndef CEPH_PAXOSSERVICE_H
+#define CEPH_PAXOSSERVICE_H
+
+#include "include/Context.h"
+#include "Paxos.h"
+#include "Monitor.h"
+#include "MonitorDBStore.h"
+
+class Monitor;
+class Paxos;
+
+/**
+ * A Paxos Service is an abstraction that easily allows one to obtain an
+ * association between a Monitor and a Paxos class, in order to implement any
+ * service.
+ */
+class PaxosService {
+ /**
+ * @defgroup PaxosService_h_class Paxos Service
+ * @{
+ */
+ public:
+ /**
+ * The Monitor to which this class is associated with
+ */
+ Monitor *mon;
+ /**
+ * The Paxos instance to which this class is associated with
+ */
+ Paxos *paxos;
+ /**
+ * Our name. This will be associated with the class implementing us, and will
+ * be used mainly for store-related operations.
+ */
+ string service_name;
+ /**
+ * If we are or have queued anything for proposal, this variable will be true
+ * until our proposal has been finished.
+ */
+ bool proposing;
+
+ bool need_immediate_propose = false;
+
+protected:
+ /**
+ * Services implementing us used to depend on the Paxos version, back when
+ * each service would have a Paxos instance for itself. However, now we only
+ * have a single Paxos instance, shared by all the services. Each service now
+ * must keep its own version, if so they wish. This variable should be used
+ * for that purpose.
+ */
+ version_t service_version;
+
+ private:
+ /**
+ * Event callback responsible for proposing our pending value once a timer
+ * runs out and fires.
+ */
+ Context *proposal_timer;
+ /**
+ * If the implementation class has anything pending to be proposed to Paxos,
+ * then have_pending should be true; otherwise, false.
+ */
+ bool have_pending;
+
+ /**
+ * health checks for this service
+ *
+ * Child must populate this during encode_pending() by calling encode_health().
+ */
+ health_check_map_t health_checks;
+protected:
+ /**
+ * format of our state in leveldb, 0 for default
+ */
+ version_t format_version;
+
+public:
+ const health_check_map_t& get_health_checks() const {
+ return health_checks;
+ }
+
+ /**
+ * @defgroup PaxosService_h_callbacks Callback classes
+ * @{
+ */
+ /**
+ * Retry dispatching a given service message
+ *
+ * This callback class is used when we had to wait for some condition to
+ * become true while we were dispatching it.
+ *
+ * For instance, if the message's version isn't readable, according to Paxos,
+ * then we must wait for it to become readable. So, we just queue an
+ * instance of this class onto the Paxos::wait_for_readable function, and
+ * we will retry the whole dispatch again once the callback is fired.
+ */
+ class C_RetryMessage : public C_MonOp {
+ PaxosService *svc;
+ public:
+ C_RetryMessage(PaxosService *s, MonOpRequestRef op_) :
+ C_MonOp(op_), svc(s) { }
+ void _finish(int r) override {
+ if (r == -EAGAIN || r >= 0)
+ svc->dispatch(op);
+ else if (r == -ECANCELED)
+ return;
+ else
+ ceph_abort_msg("bad C_RetryMessage return value");
+ }
+ };
+
+ /**
+ * @}
+ */
+
+ /**
+ * @param mn A Monitor instance
+ * @param p A Paxos instance
+ * @param name Our service's name.
+ */
+ PaxosService(Monitor *mn, Paxos *p, string name)
+ : mon(mn), paxos(p), service_name(name),
+ proposing(false),
+ service_version(0), proposal_timer(0), have_pending(false),
+ format_version(0),
+ last_committed_name("last_committed"),
+ first_committed_name("first_committed"),
+ full_prefix_name("full"), full_latest_name("latest"),
+ cached_first_committed(0), cached_last_committed(0)
+ {
+ }
+
+ virtual ~PaxosService() {}
+
+ /**
+ * Get the service's name.
+ *
+ * @returns The service's name.
+ */
+ const string& get_service_name() const { return service_name; }
+
+ /**
+ * Get the store prefixes we utilize
+ */
+ virtual void get_store_prefixes(set<string>& s) const {
+ s.insert(service_name);
+ }
+
+ // i implement and you ignore
+ /**
+ * Informs this instance that it should consider itself restarted.
+ *
+ * This means that we will cancel our proposal_timer event, if any exists.
+ */
+ void restart();
+ /**
+ * Informs this instance that an election has finished.
+ *
+ * This means that we will invoke a PaxosService::discard_pending while
+ * setting have_pending to false (basically, ignore our pending state) and
+ * we will then make sure we obtain a new state.
+ *
+ * Our state shall be updated by PaxosService::_active if the Paxos is
+ * active; otherwise, we will wait for it to become active by adding a
+ * PaxosService::C_Active callback to it.
+ */
+ void election_finished();
+ /**
+ * Informs this instance that it is supposed to shutdown.
+ *
+ * Basically, it will instruct Paxos to cancel all events/callbacks and then
+ * will cancel the proposal_timer event if any exists.
+ */
+ void shutdown();
+
+private:
+ /**
+ * Update our state by updating it from Paxos, and then creating a new
+ * pending state if need be.
+ *
+ * @remarks We only create a pending state we our Monitor is the Leader.
+ *
+ * @pre Paxos is active
+ * @post have_pending is true if our Monitor is the Leader and Paxos is
+ * active
+ */
+ void _active();
+
+public:
+ /**
+ * Propose a new value through Paxos.
+ *
+ * This function should be called by the classes implementing
+ * PaxosService, in order to propose a new value through Paxos.
+ *
+ * @pre The implementation class implements the encode_pending function.
+ * @pre have_pending is true
+ * @pre Our monitor is the Leader
+ * @pre Paxos is active
+ * @post Cancel the proposal timer, if any
+ * @post have_pending is false
+ * @post propose pending value through Paxos
+ *
+ * @note This function depends on the implementation of encode_pending on
+ * the class that is implementing PaxosService
+ */
+ void propose_pending();
+
+ /**
+ * Let others request us to propose.
+ *
+ * At the moment, this is just a wrapper to propose_pending() with an
+ * extra check for is_writeable(), but it's a good practice to dissociate
+ * requests for proposals from direct usage of propose_pending() for
+ * future use -- we might want to perform additional checks or put a
+ * request on hold, for instance.
+ */
+ void request_proposal() {
+ ceph_assert(is_writeable());
+
+ propose_pending();
+ }
+ /**
+ * Request service @p other to perform a proposal.
+ *
+ * We could simply use the function above, requesting @p other directly,
+ * but we might eventually want to do something to the request -- say,
+ * set a flag stating we're waiting on a cross-proposal to be finished.
+ */
+ void request_proposal(PaxosService *other) {
+ ceph_assert(other != NULL);
+ ceph_assert(other->is_writeable());
+
+ other->request_proposal();
+ }
+
+ /**
+ * Dispatch a message by passing it to several different functions that are
+ * either implemented directly by this service, or that should be implemented
+ * by the class implementing this service.
+ *
+ * @param m A message
+ * @returns 'true' on successful dispatch; 'false' otherwise.
+ */
+ bool dispatch(MonOpRequestRef op);
+
+ void refresh(bool *need_bootstrap);
+ void post_refresh();
+
+ /**
+ * @defgroup PaxosService_h_override_funcs Functions that should be
+ * overridden.
+ *
+ * These functions should be overridden at will by the class implementing
+ * this service.
+ * @{
+ */
+ /**
+ * Create the initial state for your system.
+ *
+ * In some of ours the state is actually set up elsewhere so this does
+ * nothing.
+ */
+ virtual void create_initial() = 0;
+
+ /**
+ * Query the Paxos system for the latest state and apply it if it's newer
+ * than the current Monitor state.
+ */
+ virtual void update_from_paxos(bool *need_bootstrap) = 0;
+
+ /**
+ * Hook called after all services have refreshed their state from paxos
+ *
+ * This is useful for doing any update work that depends on other
+ * service's having up-to-date state.
+ */
+ virtual void post_paxos_update() {}
+
+ /**
+ * Init on startup
+ *
+ * This is called on mon startup, after all of the PaxosService instances'
+ * update_from_paxos() methods have been called
+ */
+ virtual void init() {}
+
+ /**
+ * Create the pending state.
+ *
+ * @invariant This function is only called on a Leader.
+ * @remarks This created state is then modified by incoming messages.
+ * @remarks Called at startup and after every Paxos ratification round.
+ */
+ virtual void create_pending() = 0;
+
+ /**
+ * Encode the pending state into a bufferlist for ratification and
+ * transmission as the next state.
+ *
+ * @invariant This function is only called on a Leader.
+ *
+ * @param t The transaction to hold all changes.
+ */
+ virtual void encode_pending(MonitorDBStore::TransactionRef t) = 0;
+
+ /**
+ * Discard the pending state
+ *
+ * @invariant This function is only called on a Leader.
+ *
+ * @remarks This function is NOT overridden in any of our code, but it is
+ * called in PaxosService::election_finished if have_pending is
+ * true.
+ */
+ virtual void discard_pending() { }
+
+ /**
+ * Look at the query; if the query can be handled without changing state,
+ * do so.
+ *
+ * @param m A query message
+ * @returns 'true' if the query was handled (e.g., was a read that got
+ * answered, was a state change that has no effect); 'false'
+ * otherwise.
+ */
+ virtual bool preprocess_query(MonOpRequestRef op) = 0;
+
+ /**
+ * Apply the message to the pending state.
+ *
+ * @invariant This function is only called on a Leader.
+ *
+ * @param m An update message
+ * @returns 'true' if the update message was handled (e.g., a command that
+ * went through); 'false' otherwise.
+ */
+ virtual bool prepare_update(MonOpRequestRef op) = 0;
+ /**
+ * @}
+ */
+
+ /**
+ * Determine if the Paxos system should vote on pending, and if so how long
+ * it should wait to vote.
+ *
+ * @param[out] delay The wait time, used so we can limit the update traffic
+ * spamming.
+ * @returns 'true' if the Paxos system should propose; 'false' otherwise.
+ */
+ virtual bool should_propose(double &delay);
+
+ /**
+ * force an immediate propose.
+ *
+ * This is meant to be called from prepare_update(op).
+ */
+ void force_immediate_propose() {
+ need_immediate_propose = true;
+ }
+
+ /**
+ * @defgroup PaxosService_h_courtesy Courtesy functions
+ *
+ * Courtesy functions, in case the class implementing this service has
+ * anything it wants/needs to do at these times.
+ * @{
+ */
+ /**
+ * This is called when the Paxos state goes to active.
+ *
+ * On the peon, this is after each election.
+ * On the leader, this is after each election, *and* after each completed
+ * proposal.
+ *
+ * @note This function may get called twice in certain recovery cases.
+ */
+ virtual void on_active() { }
+
+ /**
+ * This is called when we are shutting down
+ */
+ virtual void on_shutdown() {}
+
+ /**
+ * this is called when activating on the leader
+ *
+ * it should conditionally upgrade the on-disk format by proposing a transaction
+ */
+ virtual void upgrade_format() { }
+
+ /**
+ * this is called when we detect the store has just upgraded underneath us
+ */
+ virtual void on_upgrade() {}
+
+ /**
+ * Called when the Paxos system enters a Leader election.
+ *
+ * @remarks It's a courtesy method, in case the class implementing this
+ * service has anything it wants/needs to do at that time.
+ */
+ virtual void on_restart() { }
+ /**
+ * @}
+ */
+
+ /**
+ * Tick.
+ */
+ virtual void tick() {}
+
+ void encode_health(const health_check_map_t& next,
+ MonitorDBStore::TransactionRef t) {
+ bufferlist bl;
+ encode(next, bl);
+ t->put("health", service_name, bl);
+ mon->log_health(next, health_checks, t);
+ }
+ void load_health();
+
+ /**
+ * @defgroup PaxosService_h_store_keys Set of keys that are usually used on
+ * all the services implementing this
+ * class, and, being almost the only keys
+ * used, should be standardized to avoid
+ * mistakes.
+ * @{
+ */
+ const string last_committed_name;
+ const string first_committed_name;
+ const string full_prefix_name;
+ const string full_latest_name;
+ /**
+ * @}
+ */
+
+ private:
+ /**
+ * @defgroup PaxosService_h_version_cache Variables holding cached values
+ * for the most used versions (first
+ * and last committed); we only have
+ * to read them when the store is
+ * updated, so in-between updates we
+ * may very well use cached versions
+ * and avoid the overhead.
+ * @{
+ */
+ version_t cached_first_committed;
+ version_t cached_last_committed;
+ /**
+ * @}
+ */
+
+ /**
+ * Callback list to be used whenever we are running a proposal through
+ * Paxos. These callbacks will be awaken whenever the said proposal
+ * finishes.
+ */
+ list<Context*> waiting_for_finished_proposal;
+
+ public:
+
+ /**
+ * Check if we are proposing a value through Paxos
+ *
+ * @returns true if we are proposing; false otherwise.
+ */
+ bool is_proposing() const {
+ return proposing;
+ }
+
+ /**
+ * Check if we are in the Paxos ACTIVE state.
+ *
+ * @note This function is a wrapper for Paxos::is_active
+ *
+ * @returns true if in state ACTIVE; false otherwise.
+ */
+ bool is_active() const {
+ return
+ !is_proposing() &&
+ (paxos->is_active() || paxos->is_updating() || paxos->is_writing());
+ }
+
+ /**
+ * Check if we are readable.
+ *
+ * This mirrors on the paxos check, except that we also verify that
+ *
+ * - the client hasn't seen the future relative to this PaxosService
+ * - this service isn't proposing.
+ * - we have committed our initial state (last_committed > 0)
+ *
+ * @param ver The version we want to check if is readable
+ * @returns true if it is readable; false otherwise
+ */
+ bool is_readable(version_t ver = 0) const {
+ if (ver > get_last_committed() ||
+ !paxos->is_readable(0) ||
+ get_last_committed() == 0)
+ return false;
+ return true;
+ }
+
+ /**
+ * Check if we are writeable.
+ *
+ * We consider to be writeable iff:
+ *
+ * - we are not proposing a new version;
+ * - we are ready to be written to -- i.e., we have a pending value.
+ * - paxos is (active or updating or writing or refresh)
+ *
+ * @returns true if writeable; false otherwise
+ */
+ bool is_writeable() const {
+ return is_active() && have_pending;
+ }
+
+ /**
+ * Wait for a proposal to finish.
+ *
+ * Add a callback to be awaken whenever our current proposal finishes being
+ * proposed through Paxos.
+ *
+ * @param c The callback to be awaken once the proposal is finished.
+ */
+ void wait_for_finished_proposal(MonOpRequestRef op, Context *c) {
+ if (op)
+ op->mark_event(service_name + ":wait_for_finished_proposal");
+ waiting_for_finished_proposal.push_back(c);
+ }
+ void wait_for_finished_proposal_ctx(Context *c) {
+ MonOpRequestRef o;
+ wait_for_finished_proposal(o, c);
+ }
+
+ /**
+ * Wait for us to become active
+ *
+ * @param c The callback to be awaken once we become active.
+ */
+ void wait_for_active(MonOpRequestRef op, Context *c) {
+ if (op)
+ op->mark_event(service_name + ":wait_for_active");
+
+ if (!is_proposing()) {
+ paxos->wait_for_active(op, c);
+ return;
+ }
+ wait_for_finished_proposal(op, c);
+ }
+ void wait_for_active_ctx(Context *c) {
+ MonOpRequestRef o;
+ wait_for_active(o, c);
+ }
+
+ /**
+ * Wait for us to become readable
+ *
+ * @param c The callback to be awaken once we become active.
+ * @param ver The version we want to wait on.
+ */
+ void wait_for_readable(MonOpRequestRef op, Context *c, version_t ver = 0) {
+ /* This is somewhat of a hack. We only do check if a version is readable on
+ * PaxosService::dispatch(), but, nonetheless, we must make sure that if that
+ * is why we are not readable, then we must wait on PaxosService and not on
+ * Paxos; otherwise, we may assert on Paxos::wait_for_readable() if it
+ * happens to be readable at that specific point in time.
+ */
+ if (op)
+ op->mark_event(service_name + ":wait_for_readable");
+
+ if (is_proposing() ||
+ ver > get_last_committed() ||
+ get_last_committed() == 0)
+ wait_for_finished_proposal(op, c);
+ else {
+ if (op)
+ op->mark_event(service_name + ":wait_for_readable/paxos");
+
+ paxos->wait_for_readable(op, c);
+ }
+ }
+
+ void wait_for_readable_ctx(Context *c, version_t ver = 0) {
+ MonOpRequestRef o; // will initialize the shared_ptr to NULL
+ wait_for_readable(o, c, ver);
+ }
+
+ /**
+ * Wait for us to become writeable
+ *
+ * @param c The callback to be awaken once we become writeable.
+ */
+ void wait_for_writeable(MonOpRequestRef op, Context *c) {
+ if (op)
+ op->mark_event(service_name + ":wait_for_writeable");
+
+ if (is_proposing())
+ wait_for_finished_proposal(op, c);
+ else if (!is_writeable())
+ wait_for_active(op, c);
+ else
+ paxos->wait_for_writeable(op, c);
+ }
+ void wait_for_writeable_ctx(Context *c) {
+ MonOpRequestRef o;
+ wait_for_writeable(o, c);
+ }
+
+
+ /**
+ * @defgroup PaxosService_h_Trim Functions for trimming states
+ * @{
+ */
+ /**
+ * trim service states if appropriate
+ *
+ * Called at same interval as tick()
+ */
+ void maybe_trim();
+
+ /**
+ * Auxiliary function to trim our state from version @p from to version
+ * @p to, not including; i.e., the interval [from, to[
+ *
+ * @param t The transaction to which we will add the trim operations.
+ * @param from the lower limit of the interval to be trimmed
+ * @param to the upper limit of the interval to be trimmed (not including)
+ */
+ void trim(MonitorDBStore::TransactionRef t, version_t from, version_t to);
+
+ /**
+ * encode service-specific extra bits into trim transaction
+ *
+ * @param tx transaction
+ * @param first new first_committed value
+ */
+ virtual void encode_trim_extra(MonitorDBStore::TransactionRef tx,
+ version_t first) {}
+
+ /**
+ * Get the version we should trim to.
+ *
+ * Should be overloaded by service if it wants to trim states.
+ *
+ * @returns the version we should trim to; if we return zero, it should be
+ * assumed that there's no version to trim to.
+ */
+ virtual version_t get_trim_to() const {
+ return 0;
+ }
+
+ /**
+ * @}
+ */
+ /**
+ * @defgroup PaxosService_h_Stash_Full
+ * @{
+ */
+ virtual bool should_stash_full();
+ /**
+ * Encode a full version on @p t
+ *
+ * @note We force every service to implement this function, since we strongly
+ * desire the encoding of full versions.
+ * @note Services that do not trim their state, will be bound to only create
+ * one full version. Full version stashing is determined/controlled by
+ * trimming: we stash a version each time a trim is bound to erase the
+ * latest full version.
+ *
+ * @param t Transaction on which the full version shall be encoded.
+ */
+ virtual void encode_full(MonitorDBStore::TransactionRef t) = 0;
+
+ /**
+ * @}
+ */
+
+ /**
+ * Cancel events.
+ *
+ * @note This function is a wrapper for Paxos::cancel_events
+ */
+ void cancel_events() {
+ paxos->cancel_events();
+ }
+
+ /**
+ * @defgroup PaxosService_h_store_funcs Back storage interface functions
+ * @{
+ */
+ /**
+ * @defgroup PaxosService_h_store_modify Wrapper function interface to access
+ * the back store for modification
+ * purposes
+ * @{
+ */
+ void put_first_committed(MonitorDBStore::TransactionRef t, version_t ver) {
+ t->put(get_service_name(), first_committed_name, ver);
+ }
+ /**
+ * Set the last committed version to @p ver
+ *
+ * @param t A transaction to which we add this put operation
+ * @param ver The last committed version number being put
+ */
+ void put_last_committed(MonitorDBStore::TransactionRef t, version_t ver) {
+ t->put(get_service_name(), last_committed_name, ver);
+
+ /* We only need to do this once, and that is when we are about to make our
+ * first proposal. There are some services that rely on first_committed
+ * being set -- and it should! -- so we need to guarantee that it is,
+ * specially because the services itself do not do it themselves. They do
+ * rely on it, but they expect us to deal with it, and so we shall.
+ */
+ if (!get_first_committed())
+ put_first_committed(t, ver);
+ }
+ /**
+ * Put the contents of @p bl into version @p ver
+ *
+ * @param t A transaction to which we will add this put operation
+ * @param ver The version to which we will add the value
+ * @param bl A bufferlist containing the version's value
+ */
+ void put_version(MonitorDBStore::TransactionRef t, version_t ver,
+ bufferlist& bl) {
+ t->put(get_service_name(), ver, bl);
+ }
+ /**
+ * Put the contents of @p bl into a full version key for this service, that
+ * will be created with @p ver in mind.
+ *
+ * @param t The transaction to which we will add this put operation
+ * @param ver A version number
+ * @param bl A bufferlist containing the version's value
+ */
+ void put_version_full(MonitorDBStore::TransactionRef t,
+ version_t ver, bufferlist& bl) {
+ string key = mon->store->combine_strings(full_prefix_name, ver);
+ t->put(get_service_name(), key, bl);
+ }
+ /**
+ * Put the version number in @p ver into the key pointing to the latest full
+ * version of this service.
+ *
+ * @param t The transaction to which we will add this put operation
+ * @param ver A version number
+ */
+ void put_version_latest_full(MonitorDBStore::TransactionRef t, version_t ver) {
+ string key = mon->store->combine_strings(full_prefix_name, full_latest_name);
+ t->put(get_service_name(), key, ver);
+ }
+ /**
+ * Put the contents of @p bl into the key @p key.
+ *
+ * @param t A transaction to which we will add this put operation
+ * @param key The key to which we will add the value
+ * @param bl A bufferlist containing the value
+ */
+ void put_value(MonitorDBStore::TransactionRef t,
+ const string& key, bufferlist& bl) {
+ t->put(get_service_name(), key, bl);
+ }
+
+ /**
+ * Put integer value @v into the key @p key.
+ *
+ * @param t A transaction to which we will add this put operation
+ * @param key The key to which we will add the value
+ * @param v An integer
+ */
+ void put_value(MonitorDBStore::TransactionRef t,
+ const string& key, version_t v) {
+ t->put(get_service_name(), key, v);
+ }
+
+ /**
+ * @}
+ */
+
+ /**
+ * @defgroup PaxosService_h_store_get Wrapper function interface to access
+ * the back store for reading purposes
+ * @{
+ */
+
+ /**
+ * @defgroup PaxosService_h_version_cache Obtain cached versions for this
+ * service.
+ * @{
+ */
+ /**
+ * Get the first committed version
+ *
+ * @returns Our first committed version (that is available)
+ */
+ version_t get_first_committed() const{
+ return cached_first_committed;
+ }
+ /**
+ * Get the last committed version
+ *
+ * @returns Our last committed version
+ */
+ version_t get_last_committed() const{
+ return cached_last_committed;
+ }
+
+ /**
+ * @}
+ */
+
+ /**
+ * Get the contents of a given version @p ver
+ *
+ * @param ver The version being obtained
+ * @param bl The bufferlist to be populated
+ * @return 0 on success; <0 otherwise
+ */
+ virtual int get_version(version_t ver, bufferlist& bl) {
+ return mon->store->get(get_service_name(), ver, bl);
+ }
+ /**
+ * Get the contents of a given full version of this service.
+ *
+ * @param ver A version number
+ * @param bl The bufferlist to be populated
+ * @returns 0 on success; <0 otherwise
+ */
+ virtual int get_version_full(version_t ver, bufferlist& bl) {
+ string key = mon->store->combine_strings(full_prefix_name, ver);
+ return mon->store->get(get_service_name(), key, bl);
+ }
+ /**
+ * Get the latest full version number
+ *
+ * @returns A version number
+ */
+ version_t get_version_latest_full() {
+ string key = mon->store->combine_strings(full_prefix_name, full_latest_name);
+ return mon->store->get(get_service_name(), key);
+ }
+
+ /**
+ * Get a value from a given key.
+ *
+ * @param[in] key The key
+ * @param[out] bl The bufferlist to be populated with the value
+ */
+ int get_value(const string& key, bufferlist& bl) {
+ return mon->store->get(get_service_name(), key, bl);
+ }
+ /**
+ * Get an integer value from a given key.
+ *
+ * @param[in] key The key
+ */
+ version_t get_value(const string& key) {
+ return mon->store->get(get_service_name(), key);
+ }
+
+ /**
+ * @}
+ */
+ /**
+ * @}
+ */
+};
+
+#endif
+
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-30 13:24:02 +0000