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/* Copyright (c) 2017, 2025, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is designed to work with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have either included with
the program or referenced in the documentation.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#include "sql_backup_lock.h"
#include <utility>
#include "m_string.h"
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_sys.h"
#include "mysqld_error.h" // ER_SPECIFIC_ACCESS_DENIED_ERROR
#include "sql/auth/sql_security_ctx.h" // Security_context
#include "sql/mdl.h"
#include "sql/system_variables.h"
#include "sql_class.h" // THD
/**
Check if a current user has the privilege BACKUP_ADMIN required to run
the statement LOCK INSTANCE FOR BACKUP.
@param thd Current thread
@retval false A user has the privilege BACKUP_ADMIN
@retval true A user doesn't have the privilege BACKUP_ADMIN
*/
static bool check_backup_admin_privilege(THD *thd) {
Security_context *sctx = thd->security_context();
if (!sctx->has_global_grant(STRING_WITH_LEN("BACKUP_ADMIN")).first) {
my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "BACKUP_ADMIN");
return true;
}
return false;
}
bool Sql_cmd_lock_instance::execute(THD *thd) {
if (check_backup_admin_privilege(thd) ||
acquire_exclusive_backup_lock(
thd,
DBUG_EVALUATE_IF("stop_replica_dont_release_backup_lock", 5,
thd->variables.lock_wait_timeout),
false))
return true;
my_ok(thd);
return false;
}
bool Sql_cmd_unlock_instance::execute(THD *thd) {
if (check_backup_admin_privilege(thd)) return true;
release_backup_lock(thd);
my_ok(thd);
return false;
}
Shared_backup_lock_guard::Shared_backup_lock_guard(THD *thd) : m_thd(thd) {
// If instance is locked for the backup, then even block operations requisting
// shared backup lock. For example, PURGE BINARY LOG is not allowed even when
// instance is locked for backup by the same session.
if (thd->mdl_context.owns_equal_or_stronger_lock(MDL_key::BACKUP_LOCK, "", "",
MDL_SHARED)) {
m_lock_state = Shared_backup_lock_guard::Lock_result::not_locked;
return;
}
m_lock_state = try_acquire_shared_backup_lock(m_thd, false);
}
Shared_backup_lock_guard::~Shared_backup_lock_guard() {
if (m_lock_state == Shared_backup_lock_guard::Lock_result::locked) {
release_backup_lock(m_thd);
}
}
Shared_backup_lock_guard::operator Shared_backup_lock_guard::Lock_result()
const {
return m_lock_state;
}
Shared_backup_lock_guard::Lock_result
Shared_backup_lock_guard::try_acquire_shared_backup_lock(THD *thd,
bool for_trx) {
MDL_request mdl_request;
const enum_mdl_duration duration = (for_trx ? MDL_TRANSACTION : MDL_EXPLICIT);
MDL_REQUEST_INIT(&mdl_request, MDL_key::BACKUP_LOCK, "", "",
MDL_INTENTION_EXCLUSIVE, duration);
if (thd->mdl_context.try_acquire_lock(&mdl_request)) {
return Shared_backup_lock_guard::Lock_result::oom;
}
if (mdl_request.ticket == nullptr) {
return Shared_backup_lock_guard::Lock_result::not_locked;
}
return Shared_backup_lock_guard::Lock_result::locked;
}
/**
Acquire either exclusive or shared Backup Lock.
@param[in] thd Current thread context
@param[in] mdl_type Type of metadata lock to acquire for backup
@param[in] mdl_duration Duration of metadata lock
@param[in] lock_wait_timeout How many seconds to wait before timeout.
@return Operation status.
@retval false Success
@retval true Failure
*/
static bool acquire_mdl_for_backup(THD *thd, enum_mdl_type mdl_type,
enum_mdl_duration mdl_duration,
ulong lock_wait_timeout) {
MDL_request mdl_request;
assert(mdl_type == MDL_SHARED || mdl_type == MDL_INTENTION_EXCLUSIVE);
MDL_REQUEST_INIT(&mdl_request, MDL_key::BACKUP_LOCK, "", "", mdl_type,
mdl_duration);
return thd->mdl_context.acquire_lock(&mdl_request, lock_wait_timeout);
}
/**
MDL_release_locks_visitor subclass to release MDL for BACKUP_LOCK.
*/
class Release_all_backup_locks : public MDL_release_locks_visitor {
public:
bool release(MDL_ticket *ticket) override {
return ticket->get_key()->mdl_namespace() == MDL_key::BACKUP_LOCK;
}
};
void release_backup_lock(THD *thd) {
Release_all_backup_locks lock_visitor;
thd->mdl_context.release_locks(&lock_visitor);
}
/*
The following rationale is for justification of choice for specific lock
types to support BACKUP LOCK.
IX and S locks are mutually incompatible. On the other hand both these
lock types are compatible with themselves. IX lock has lower priority
than S locks. So we can use S lock for rare Backup operation which should
not be starved by more frequent DDL operations using IX locks.
From all listed above follows that S lock should be considered as Exclusive
Backup Lock and IX lock should be considered as Shared Backup Lock.
*/
bool acquire_exclusive_backup_lock(THD *thd, ulong lock_wait_timeout,
bool for_trx) {
enum_mdl_duration duration = (for_trx ? MDL_TRANSACTION : MDL_EXPLICIT);
return acquire_mdl_for_backup(thd, MDL_SHARED, duration, lock_wait_timeout);
}
bool acquire_shared_backup_lock(THD *thd, ulong lock_wait_timeout,
bool for_trx) {
enum_mdl_duration duration = (for_trx ? MDL_TRANSACTION : MDL_EXPLICIT);
return acquire_mdl_for_backup(thd, MDL_INTENTION_EXCLUSIVE, duration,
lock_wait_timeout);
}
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