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

2 files changed, 36 insertions, 13 deletions

diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
index 32d3a4b0853..6d452ec6d95 100644
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -89,6 +89,37 @@ typedef struct
 #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
  * backend is run.  The Port structure is kept in malloc'd memory and is
@@ -149,19 +180,6 @@ 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.
 	 *
 	 * default values are 0 if AF_UNIX or not yet known; current values are 0
@@ -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. */
 
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 7c41b279942..65cf4ba50f3 100644
--- a/src/include/miscadmin.h
+++ b/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);