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-rw-r--r--src/backend/commands/lockcmds.c294
1 files changed, 294 insertions, 0 deletions
diff --git a/src/backend/commands/lockcmds.c b/src/backend/commands/lockcmds.c
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+/*-------------------------------------------------------------------------
+ *
+ * lockcmds.c
+ * LOCK command support code
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * src/backend/commands/lockcmds.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/table.h"
+#include "access/xact.h"
+#include "catalog/namespace.h"
+#include "catalog/pg_inherits.h"
+#include "commands/lockcmds.h"
+#include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
+#include "parser/parse_clause.h"
+#include "rewrite/rewriteHandler.h"
+#include "storage/lmgr.h"
+#include "utils/acl.h"
+#include "utils/lsyscache.h"
+#include "utils/syscache.h"
+
+static void LockTableRecurse(Oid reloid, LOCKMODE lockmode, bool nowait);
+static AclResult LockTableAclCheck(Oid relid, LOCKMODE lockmode, Oid userid);
+static void RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid,
+ Oid oldrelid, void *arg);
+static void LockViewRecurse(Oid reloid, LOCKMODE lockmode, bool nowait,
+ List *ancestor_views);
+
+/*
+ * LOCK TABLE
+ */
+void
+LockTableCommand(LockStmt *lockstmt)
+{
+ ListCell *p;
+
+ /*
+ * Iterate over the list and process the named relations one at a time
+ */
+ foreach(p, lockstmt->relations)
+ {
+ RangeVar *rv = (RangeVar *) lfirst(p);
+ bool recurse = rv->inh;
+ Oid reloid;
+
+ reloid = RangeVarGetRelidExtended(rv, lockstmt->mode,
+ lockstmt->nowait ? RVR_NOWAIT : 0,
+ RangeVarCallbackForLockTable,
+ (void *) &lockstmt->mode);
+
+ if (get_rel_relkind(reloid) == RELKIND_VIEW)
+ LockViewRecurse(reloid, lockstmt->mode, lockstmt->nowait, NIL);
+ else if (recurse)
+ LockTableRecurse(reloid, lockstmt->mode, lockstmt->nowait);
+ }
+}
+
+/*
+ * Before acquiring a table lock on the named table, check whether we have
+ * permission to do so.
+ */
+static void
+RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid, Oid oldrelid,
+ void *arg)
+{
+ LOCKMODE lockmode = *(LOCKMODE *) arg;
+ char relkind;
+ char relpersistence;
+ AclResult aclresult;
+
+ if (!OidIsValid(relid))
+ return; /* doesn't exist, so no permissions check */
+ relkind = get_rel_relkind(relid);
+ if (!relkind)
+ return; /* woops, concurrently dropped; no permissions
+ * check */
+
+ /* Currently, we only allow plain tables or views to be locked */
+ if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE &&
+ relkind != RELKIND_VIEW)
+ ereport(ERROR,
+ (errcode(ERRCODE_WRONG_OBJECT_TYPE),
+ errmsg("\"%s\" is not a table or view",
+ rv->relname)));
+
+ /*
+ * Make note if a temporary relation has been accessed in this
+ * transaction.
+ */
+ relpersistence = get_rel_persistence(relid);
+ if (relpersistence == RELPERSISTENCE_TEMP)
+ MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
+
+ /* Check permissions. */
+ aclresult = LockTableAclCheck(relid, lockmode, GetUserId());
+ if (aclresult != ACLCHECK_OK)
+ aclcheck_error(aclresult, get_relkind_objtype(get_rel_relkind(relid)), rv->relname);
+}
+
+/*
+ * Apply LOCK TABLE recursively over an inheritance tree
+ *
+ * This doesn't check permission to perform LOCK TABLE on the child tables,
+ * because getting here means that the user has permission to lock the
+ * parent which is enough.
+ */
+static void
+LockTableRecurse(Oid reloid, LOCKMODE lockmode, bool nowait)
+{
+ List *children;
+ ListCell *lc;
+
+ children = find_all_inheritors(reloid, NoLock, NULL);
+
+ foreach(lc, children)
+ {
+ Oid childreloid = lfirst_oid(lc);
+
+ /* Parent already locked. */
+ if (childreloid == reloid)
+ continue;
+
+ if (!nowait)
+ LockRelationOid(childreloid, lockmode);
+ else if (!ConditionalLockRelationOid(childreloid, lockmode))
+ {
+ /* try to throw error by name; relation could be deleted... */
+ char *relname = get_rel_name(childreloid);
+
+ if (!relname)
+ continue; /* child concurrently dropped, just skip it */
+ ereport(ERROR,
+ (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+ errmsg("could not obtain lock on relation \"%s\"",
+ relname)));
+ }
+
+ /*
+ * Even if we got the lock, child might have been concurrently
+ * dropped. If so, we can skip it.
+ */
+ if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(childreloid)))
+ {
+ /* Release useless lock */
+ UnlockRelationOid(childreloid, lockmode);
+ continue;
+ }
+ }
+}
+
+/*
+ * Apply LOCK TABLE recursively over a view
+ *
+ * All tables and views appearing in the view definition query are locked
+ * recursively with the same lock mode.
+ */
+
+typedef struct
+{
+ LOCKMODE lockmode; /* lock mode to use */
+ bool nowait; /* no wait mode */
+ Oid viewowner; /* view owner for checking the privilege */
+ Oid viewoid; /* OID of the view to be locked */
+ List *ancestor_views; /* OIDs of ancestor views */
+} LockViewRecurse_context;
+
+static bool
+LockViewRecurse_walker(Node *node, LockViewRecurse_context *context)
+{
+ if (node == NULL)
+ return false;
+
+ if (IsA(node, Query))
+ {
+ Query *query = (Query *) node;
+ ListCell *rtable;
+
+ foreach(rtable, query->rtable)
+ {
+ RangeTblEntry *rte = lfirst(rtable);
+ AclResult aclresult;
+
+ Oid relid = rte->relid;
+ char relkind = rte->relkind;
+ char *relname = get_rel_name(relid);
+
+ /*
+ * The OLD and NEW placeholder entries in the view's rtable are
+ * skipped.
+ */
+ if (relid == context->viewoid &&
+ (strcmp(rte->eref->aliasname, "old") == 0 ||
+ strcmp(rte->eref->aliasname, "new") == 0))
+ continue;
+
+ /* Currently, we only allow plain tables or views to be locked. */
+ if (relkind != RELKIND_RELATION && relkind != RELKIND_PARTITIONED_TABLE &&
+ relkind != RELKIND_VIEW)
+ continue;
+
+ /*
+ * We might be dealing with a self-referential view. If so, we
+ * can just stop recursing, since we already locked it.
+ */
+ if (list_member_oid(context->ancestor_views, relid))
+ continue;
+
+ /* Check permissions with the view owner's privilege. */
+ aclresult = LockTableAclCheck(relid, context->lockmode, context->viewowner);
+ if (aclresult != ACLCHECK_OK)
+ aclcheck_error(aclresult, get_relkind_objtype(relkind), relname);
+
+ /* We have enough rights to lock the relation; do so. */
+ if (!context->nowait)
+ LockRelationOid(relid, context->lockmode);
+ else if (!ConditionalLockRelationOid(relid, context->lockmode))
+ ereport(ERROR,
+ (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+ errmsg("could not obtain lock on relation \"%s\"",
+ relname)));
+
+ if (relkind == RELKIND_VIEW)
+ LockViewRecurse(relid, context->lockmode, context->nowait,
+ context->ancestor_views);
+ else if (rte->inh)
+ LockTableRecurse(relid, context->lockmode, context->nowait);
+ }
+
+ return query_tree_walker(query,
+ LockViewRecurse_walker,
+ context,
+ QTW_IGNORE_JOINALIASES);
+ }
+
+ return expression_tree_walker(node,
+ LockViewRecurse_walker,
+ context);
+}
+
+static void
+LockViewRecurse(Oid reloid, LOCKMODE lockmode, bool nowait,
+ List *ancestor_views)
+{
+ LockViewRecurse_context context;
+ Relation view;
+ Query *viewquery;
+
+ /* caller has already locked the view */
+ view = table_open(reloid, NoLock);
+ viewquery = get_view_query(view);
+
+ context.lockmode = lockmode;
+ context.nowait = nowait;
+ context.viewowner = view->rd_rel->relowner;
+ context.viewoid = reloid;
+ context.ancestor_views = lappend_oid(ancestor_views, reloid);
+
+ LockViewRecurse_walker((Node *) viewquery, &context);
+
+ context.ancestor_views = list_delete_last(context.ancestor_views);
+
+ table_close(view, NoLock);
+}
+
+/*
+ * Check whether the current user is permitted to lock this relation.
+ */
+static AclResult
+LockTableAclCheck(Oid reloid, LOCKMODE lockmode, Oid userid)
+{
+ AclResult aclresult;
+ AclMode aclmask;
+
+ /* Verify adequate privilege */
+ if (lockmode == AccessShareLock)
+ aclmask = ACL_SELECT;
+ else if (lockmode == RowExclusiveLock)
+ aclmask = ACL_INSERT | ACL_UPDATE | ACL_DELETE | ACL_TRUNCATE;
+ else
+ aclmask = ACL_UPDATE | ACL_DELETE | ACL_TRUNCATE;
+
+ aclresult = pg_class_aclcheck(reloid, userid, aclmask);
+
+ return aclresult;
+}
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