Allow parallel workers to retrieve some data from Port

This commit moves authn_id into a new global structure called
ClientConnectionInfo (mapping to a MyClientConnectionInfo for each
backend) which is intended to hold all the client information that
should be shared between the backend and any of its parallel workers,
access for extensions and triggers being the primary use case.  There is
no need to push all the data of Port to the workers, and authn_id is
quite a generic concept so using a separate structure provides the best
balance (the name of the structure has been suggested by Robert Haas).

While on it, and per discussion as this would be useful for a potential
SYSTEM_USER that can be accessed through parallel workers, a second
field is added for the authentication method, copied directly from
Port.

ClientConnectionInfo is serialized and restored using a new parallel
key and a structure tracks the length of the authn_id, making the
addition of more fields straight-forward.

Author: Jacob Champion
Reviewed-by: Bertrand Drouvot, Stephen Frost, Robert Haas, Tom Lane,
Michael Paquier, Julien Rouhaud
Discussion: https://postgr.es/m/793d990837ae5c06a558d58d62de9378ab525d83.camel@vmware.com

src/backend/access/transam/parallel.c

@@ -76,6 +76,7 @@
 #define PARALLEL_KEY_REINDEX_STATE			UINT64CONST(0xFFFFFFFFFFFF000C)
 #define PARALLEL_KEY_RELMAPPER_STATE		UINT64CONST(0xFFFFFFFFFFFF000D)
 #define PARALLEL_KEY_UNCOMMITTEDENUMS		UINT64CONST(0xFFFFFFFFFFFF000E)
+#define PARALLEL_KEY_CLIENTCONNINFO			UINT64CONST(0xFFFFFFFFFFFF000F)
 
 /* Fixed-size parallel state. */
 typedef struct FixedParallelState
@@ -212,6 +213,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
 	Size		reindexlen = 0;
 	Size		relmapperlen = 0;
 	Size		uncommittedenumslen = 0;
+	Size		clientconninfolen = 0;
 	Size		segsize = 0;
 	int			i;
 	FixedParallelState *fps;
@@ -272,8 +274,10 @@ InitializeParallelDSM(ParallelContext *pcxt)
 		shm_toc_estimate_chunk(&pcxt->estimator, relmapperlen);
 		uncommittedenumslen = EstimateUncommittedEnumsSpace();
 		shm_toc_estimate_chunk(&pcxt->estimator, uncommittedenumslen);
+		clientconninfolen = EstimateClientConnectionInfoSpace();
+		shm_toc_estimate_chunk(&pcxt->estimator, clientconninfolen);
 		/* If you add more chunks here, you probably need to add keys. */
-		shm_toc_estimate_keys(&pcxt->estimator, 11);
+		shm_toc_estimate_keys(&pcxt->estimator, 12);
 
 		/* Estimate space need for error queues. */
 		StaticAssertStmt(BUFFERALIGN(PARALLEL_ERROR_QUEUE_SIZE) ==
@@ -352,6 +356,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
 		char	   *session_dsm_handle_space;
 		char	   *entrypointstate;
 		char	   *uncommittedenumsspace;
+		char	   *clientconninfospace;
 		Size		lnamelen;
 
 		/* Serialize shared libraries we have loaded. */
@@ -422,6 +427,12 @@ InitializeParallelDSM(ParallelContext *pcxt)
 		shm_toc_insert(pcxt->toc, PARALLEL_KEY_UNCOMMITTEDENUMS,
 					   uncommittedenumsspace);
 
+		/* Serialize our ClientConnectionInfo. */
+		clientconninfospace = shm_toc_allocate(pcxt->toc, clientconninfolen);
+		SerializeClientConnectionInfo(clientconninfolen, clientconninfospace);
+		shm_toc_insert(pcxt->toc, PARALLEL_KEY_CLIENTCONNINFO,
+					   clientconninfospace);
+
 		/* Allocate space for worker information. */
 		pcxt->worker = palloc0(sizeof(ParallelWorkerInfo) * pcxt->nworkers);
 
@@ -1270,6 +1281,7 @@ ParallelWorkerMain(Datum main_arg)
 	char	   *reindexspace;
 	char	   *relmapperspace;
 	char	   *uncommittedenumsspace;
+	char	   *clientconninfospace;
 	StringInfoData msgbuf;
 	char	   *session_dsm_handle_space;
 	Snapshot	tsnapshot;
@@ -1479,6 +1491,11 @@ ParallelWorkerMain(Datum main_arg)
 										   false);
 	RestoreUncommittedEnums(uncommittedenumsspace);
 
+	/* Restore the ClientConnectionInfo. */
+	clientconninfospace = shm_toc_lookup(toc, PARALLEL_KEY_CLIENTCONNINFO,
+										 false);
+	RestoreClientConnectionInfo(clientconninfospace);
+
 	/* Attach to the leader's serializable transaction, if SERIALIZABLE. */
 	AttachSerializableXact(fps->serializable_xact_handle);
 

src/backend/libpq/auth.c

@@ -333,23 +333,23 @@ auth_failed(Port *port, int status, const char *logdetail)
 
 /*
  * Sets the authenticated identity for the current user.  The provided string
- * will be copied into the TopMemoryContext.  The ID will be logged if
- * log_connections is enabled.
+ * will be stored into MyClientConnectionInfo, alongside the current HBA
+ * method in use.  The ID will be logged if log_connections is enabled.
  *
  * Auth methods should call this routine exactly once, as soon as the user is
  * successfully authenticated, even if they have reasons to know that
  * authorization will fail later.
  *
  * The provided string will be copied into TopMemoryContext, to match the
- * lifetime of the Port, so it is safe to pass a string that is managed by an
- * external library.
+ * lifetime of MyClientConnectionInfo, so it is safe to pass a string that is
+ * managed by an external library.
  */
 static void
 set_authn_id(Port *port, const char *id)
 {
 	Assert(id);
 
-	if (port->authn_id)
+	if (MyClientConnectionInfo.authn_id)
 	{
 		/*
 		 * An existing authn_id should never be overwritten; that means two
@@ -360,18 +360,20 @@ set_authn_id(Port *port, const char *id)
 		ereport(FATAL,
 				(errmsg("authentication identifier set more than once"),
 				 errdetail_log("previous identifier: \"%s\"; new identifier: \"%s\"",
-							   port->authn_id, id)));
+							   MyClientConnectionInfo.authn_id, id)));
 	}
 
-	port->authn_id = MemoryContextStrdup(TopMemoryContext, id);
+	MyClientConnectionInfo.authn_id = MemoryContextStrdup(TopMemoryContext, id);
+	MyClientConnectionInfo.auth_method = port->hba->auth_method;
 
 	if (Log_connections)
 	{
 		ereport(LOG,
 				errmsg("connection authenticated: identity=\"%s\" method=%s "
 					   "(%s:%d)",
-					   port->authn_id, hba_authname(port->hba->auth_method), HbaFileName,
-					   port->hba->linenumber));
+					   MyClientConnectionInfo.authn_id,
+					   hba_authname(MyClientConnectionInfo.auth_method),
+					   HbaFileName, port->hba->linenumber));
 	}
 }
 
@@ -1907,7 +1909,8 @@ auth_peer(hbaPort *port)
 	 */
 	set_authn_id(port, pw->pw_name);
 
-	ret = check_usermap(port->hba->usermap, port->user_name, port->authn_id, false);
+	ret = check_usermap(port->hba->usermap, port->user_name,
+						MyClientConnectionInfo.authn_id, false);
 
 	return ret;
 #else

src/backend/postmaster/postmaster.c

@@ -4305,6 +4305,7 @@ BackendInitialize(Port *port)
 
 	/* Save port etc. for ps status */
 	MyProcPort = port;
+	memset(&MyClientConnectionInfo, 0, sizeof(MyClientConnectionInfo));
 
 	/* Tell fd.c about the long-lived FD associated with the port */
 	ReserveExternalFD();

src/backend/utils/init/miscinit.c

@@ -936,6 +936,99 @@ GetUserNameFromId(Oid roleid, bool noerr)
 	return result;
 }
 
+/* ------------------------------------------------------------------------
+ *				Client connection state shared with parallel workers
+ *
+ * ClientConnectionInfo contains pieces of information about the client that
+ * need to be synced to parallel workers when they initialize.
+ *-------------------------------------------------------------------------
+ */
+
+ClientConnectionInfo MyClientConnectionInfo;
+
+/*
+ * Intermediate representation of ClientConnectionInfo for easier
+ * serialization.  Variable-length fields are allocated right after this
+ * header.
+ */
+typedef struct SerializedClientConnectionInfo
+{
+	int32		authn_id_len;	/* strlen(authn_id), or -1 if NULL */
+	UserAuth	auth_method;
+} SerializedClientConnectionInfo;
+
+/*
+ * Calculate the space needed to serialize MyClientConnectionInfo.
+ */
+Size
+EstimateClientConnectionInfoSpace(void)
+{
+	Size		size = 0;
+
+	size = add_size(size, sizeof(SerializedClientConnectionInfo));
+
+	if (MyClientConnectionInfo.authn_id)
+		size = add_size(size, strlen(MyClientConnectionInfo.authn_id) + 1);
+
+	return size;
+}
+
+/*
+ * Serialize MyClientConnectionInfo for use by parallel workers.
+ */
+void
+SerializeClientConnectionInfo(Size maxsize, char *start_address)
+{
+	SerializedClientConnectionInfo serialized = {0};
+
+	serialized.authn_id_len = -1;
+	serialized.auth_method = MyClientConnectionInfo.auth_method;
+
+	if (MyClientConnectionInfo.authn_id)
+		serialized.authn_id_len = strlen(MyClientConnectionInfo.authn_id);
+
+	/* Copy serialized representation to buffer */
+	Assert(maxsize >= sizeof(serialized));
+	memcpy(start_address, &serialized, sizeof(serialized));
+
+	maxsize -= sizeof(serialized);
+	start_address += sizeof(serialized);
+
+	/* Copy authn_id into the space after the struct */
+	if (serialized.authn_id_len >= 0)
+	{
+		Assert(maxsize >= (serialized.authn_id_len + 1));
+		memcpy(start_address,
+			   MyClientConnectionInfo.authn_id,
+		/* include the NULL terminator to ease deserialization */
+			   serialized.authn_id_len + 1);
+	}
+}
+
+/*
+ * Restore MyClientConnectionInfo from its serialized representation.
+ */
+void
+RestoreClientConnectionInfo(char *conninfo)
+{
+	SerializedClientConnectionInfo serialized;
+
+	memcpy(&serialized, conninfo, sizeof(serialized));
+
+	/* Copy the fields back into place */
+	MyClientConnectionInfo.authn_id = NULL;
+	MyClientConnectionInfo.auth_method = serialized.auth_method;
+
+	if (serialized.authn_id_len >= 0)
+	{
+		char	   *authn_id;
+
+		authn_id = conninfo + sizeof(serialized);
+		MyClientConnectionInfo.authn_id = MemoryContextStrdup(TopMemoryContext,
+															  authn_id);
+	}
+}
+
 
 /*-------------------------------------------------------------------------
  *				Interlock-file support

src/include/libpq/libpq-be.h

@@ -88,6 +88,37 @@ typedef struct
 } pg_gssinfo;
 #endif
 
+/*
+ * ClientConnectionInfo includes the fields describing the client connection
+ * that are copied over to parallel workers as nothing from Port does that.
+ * The same rules apply for allocations here as for Port (everything must be
+ * malloc'd or palloc'd in TopMemoryContext).
+ *
+ * If you add a struct member here, remember to also handle serialization in
+ * SerializeClientConnectionInfo() and co.
+ */
+typedef struct ClientConnectionInfo
+{
+	/*
+	 * Authenticated identity.  The meaning of this identifier is dependent on
+	 * auth_method; it is the identity (if any) that the user presented during
+	 * the authentication cycle, before they were assigned a database role.
+	 * (It is effectively the "SYSTEM-USERNAME" of a pg_ident usermap --
+	 * though the exact string in use may be different, depending on pg_hba
+	 * options.)
+	 *
+	 * authn_id is NULL if the user has not actually been authenticated, for
+	 * example if the "trust" auth method is in use.
+	 */
+	const char *authn_id;
+
+	/*
+	 * The HBA method that determined the above authn_id.  This only has
+	 * meaning if authn_id is not NULL; otherwise it's undefined.
+	 */
+	UserAuth	auth_method;
+} ClientConnectionInfo;
+
 /*
  * This is used by the postmaster in its communication with frontends.  It
  * contains all state information needed during this communication before the
@@ -148,19 +179,6 @@ typedef struct Port
 	 */
 	HbaLine    *hba;
 
-	/*
-	 * Authenticated identity.  The meaning of this identifier is dependent on
-	 * hba->auth_method; it is the identity (if any) that the user presented
-	 * during the authentication cycle, before they were assigned a database
-	 * role.  (It is effectively the "SYSTEM-USERNAME" of a pg_ident usermap
-	 * -- though the exact string in use may be different, depending on pg_hba
-	 * options.)
-	 *
-	 * authn_id is NULL if the user has not actually been authenticated, for
-	 * example if the "trust" auth method is in use.
-	 */
-	const char *authn_id;
-
 	/*
 	 * TCP keepalive and user timeout settings.
 	 *
@@ -317,6 +335,7 @@ extern ssize_t be_gssapi_write(Port *port, void *ptr, size_t len);
 #endif							/* ENABLE_GSS */
 
 extern PGDLLIMPORT ProtocolVersion FrontendProtocol;
+extern PGDLLIMPORT ClientConnectionInfo MyClientConnectionInfo;
 
 /* TCP keepalives configuration. These are no-ops on an AF_UNIX socket. */
 

src/include/miscadmin.h

@@ -482,6 +482,10 @@ extern bool has_rolreplication(Oid roleid);
 typedef void (*shmem_request_hook_type) (void);
 extern PGDLLIMPORT shmem_request_hook_type shmem_request_hook;
 
+extern Size EstimateClientConnectionInfoSpace(void);
+extern void SerializeClientConnectionInfo(Size maxsize, char *start_address);
+extern void RestoreClientConnectionInfo(char *conninfo);
+
 /* in executor/nodeHash.c */
 extern size_t get_hash_memory_limit(void);
 

src/tools/pgindent/typedefs.list

@@ -373,6 +373,7 @@ CkptTsStatus
 ClientAuthentication_hook_type
 ClientCertMode
 ClientCertName
+ClientConnectionInfo
 ClientData
 ClonePtrType
 ClosePortalStmt
@@ -2455,6 +2456,7 @@ SerCommitSeqNo
 SerialControl
 SerializableXactHandle
 SerializedActiveRelMaps
+SerializedClientConnectionInfo
 SerializedRanges
 SerializedReindexState
 SerializedSnapshotData