Add hook functions for diskquota extension.

Diskquota extension needs two kinds of hooks:
1. hooks to detect active tables when tables are being modified.
2. hooks to cancel a query whose quota limit is reached.

These two kinds of hooks are described in detail in Wiki:
https://github.com/greenplum-db/gpdb/wiki/Greenplum-Diskquota-Design#design-of-diskquota
They are corresponding to two components: Quota Enforcement Operator
and Quota Change Detector.
Co-authored-by: NHaozhou Wang <hawang@pivotal.io>
Co-authored-by: NHao Wu <gfphoenix78@gmail.com>

src/backend/cdb/cdbbufferedappend.c

@@ -23,6 +23,11 @@
 #include "cdb/cdbbufferedappend.h"
 #include "utils/guc.h"
 
+/*
+ * Hook function in BufferedAppendWrite, used by plugins to call
+ * when the size of AO table is increased.
+ */
+BufferedAppendWrite_hook_type BufferedAppendWrite_hook = NULL;
 static void BufferedAppendWrite(
 					BufferedAppend *bufferedAppend,
 					bool needsWAL);
@@ -196,6 +201,8 @@ BufferedAppendWrite(BufferedAppend *bufferedAppend, bool needsWAL)
 		   bufferedAppend->filePathName,
 		   bufferedAppend->largeWritePosition,
 		   bytestotal);
+	if (BufferedAppendWrite_hook)
+		(*BufferedAppendWrite_hook)(bufferedAppend);
 
 	/*
 	 * Log each varblock to the XLog. Write to the file first, before

src/backend/cdb/dispatcher/cdbdisp_async.c

@@ -48,6 +48,8 @@
  */
 #define DISPATCH_WAIT_CANCEL_TIMEOUT_MSEC 100
 
+DispatcherCheckPerms_hook_type DispatcherCheckPerms_hook = NULL;
+
 typedef struct CdbDispatchCmdAsync
 {
 
@@ -539,6 +541,12 @@ checkDispatchResult(CdbDispatcherState *ds,
 				checkSegmentAlive(pParms);
 			}
 
+			/* Hook to check permissions when dispatcher timeout */
+			if (DispatcherCheckPerms_hook && pParms->waitMode == DISPATCH_WAIT_NONE)
+			{
+				(*DispatcherCheckPerms_hook)();
+			}
+
 			if (!wait)
 				break;
 		}

src/backend/storage/smgr/smgr.c

@@ -32,6 +32,16 @@
 #include "utils/hsearch.h"
 #include "utils/inval.h"
 
+/*
+ * Hook for plugins to extend smgr functions.
+ * for example, collect statistics from smgr functions
+ * via recording the active relfilenode information.
+ */
+smgrcreate_hook_type smgrcreate_hook = NULL;
+smgrextend_hook_type smgrextend_hook = NULL;
+smgrtruncate_hook_type smgrtruncate_hook = NULL;
+smgrdounlinkall_hook_type smgrdounlinkall_hook = NULL;
+
 /*
  * Each backend has a hashtable that stores all extant SMgrRelation objects.
  * In addition, "unowned" SMgrRelation objects are chained together in a list.
@@ -329,6 +339,11 @@ smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo)
 	if (isRedo && reln->md_fd[forknum] != NULL)
 		return;
 
+	if (smgrcreate_hook)
+	{
+		(*smgrcreate_hook)(reln, forknum, isRedo);
+	}
+
 	/*
 	 * We may be using the target table space for the first time in this
 	 * database, so create a per-database subdirectory if needed.
@@ -445,6 +460,11 @@ smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo, char *relstorages)
 	if (nrels == 0)
 		return;
 
+	if (smgrdounlinkall_hook)
+	{
+		(*smgrdounlinkall_hook)(rels, nrels, isRedo, relstorages);
+	}
+
 	/*
 	 * create an array which contains all relations to be dropped, and close
 	 * each relation's forks at the smgr level while at it
@@ -519,6 +539,11 @@ void
 smgrextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
 		   char *buffer, bool skipFsync)
 {
+	if (smgrextend_hook)
+	{
+		(*smgrextend_hook)(reln, forknum, blocknum, buffer, skipFsync);
+	}
+
 	mdextend(reln, forknum, blocknum, buffer, skipFsync);
 }
 
@@ -587,6 +612,11 @@ smgrnblocks(SMgrRelation reln, ForkNumber forknum)
 void
 smgrtruncate(SMgrRelation reln, ForkNumber forknum, BlockNumber nblocks)
 {
+	if (smgrtruncate_hook)
+	{
+		(*smgrtruncate_hook)(reln, forknum, nblocks);
+	}
+
 	/*
 	 * Get rid of any buffers for the about-to-be-deleted blocks. bufmgr will
 	 * just drop them without bothering to write the contents.

src/include/cdb/cdbbufferedappend.h

@@ -182,4 +182,8 @@ extern void BufferedAppendCompleteFile(
 extern void BufferedAppendFinish(
     BufferedAppend *bufferedAppend);
 
+/* Hook type and declaration in BufferedAppendWrite */
+typedef void (*BufferedAppendWrite_hook_type)(BufferedAppend *bufferedAppend);
+extern PGDLLIMPORT BufferedAppendWrite_hook_type BufferedAppendWrite_hook;
+
 #endif   /* CDBBUFFEREDAPPEND_H */

src/include/cdb/cdbdisp_async.h

@@ -18,4 +18,12 @@
 
 extern DispatcherInternalFuncs DispatcherAsyncFuncs;
 
+/*
+ * Hook for plugins to check permissions in dispatcher
+ * One example is to check whether disk quota limit is 
+ * exceeded for the table which is loading data.
+ */
+typedef bool (*DispatcherCheckPerms_hook_type) (void);
+extern PGDLLIMPORT DispatcherCheckPerms_hook_type DispatcherCheckPerms_hook;
+
 #endif

src/include/storage/smgr.h

@@ -146,4 +146,32 @@ extern Datum smgrin(PG_FUNCTION_ARGS);
 extern Datum smgreq(PG_FUNCTION_ARGS);
 extern Datum smgrne(PG_FUNCTION_ARGS);
 
+/*
+ * Hook for plugins to extend smgr functions.
+ * for example, collect statistics from smgr functions
+ * via recording the active relfilenode information.
+ */
+typedef void (*smgrcreate_hook_type)(SMgrRelation reln,
+									 ForkNumber forknum,
+									 bool isRedo);
+extern PGDLLIMPORT smgrcreate_hook_type smgrcreate_hook;
+
+typedef void (*smgrextend_hook_type)(SMgrRelation reln,
+									 ForkNumber forknum,
+									 BlockNumber blocknum,
+									 char *buffer,
+									 bool skipFsync);
+extern PGDLLIMPORT smgrextend_hook_type smgrextend_hook;
+
+typedef void (*smgrtruncate_hook_type)(SMgrRelation reln,
+									   ForkNumber forknum,
+									   BlockNumber nblocks);
+extern PGDLLIMPORT smgrtruncate_hook_type smgrtruncate_hook;
+
+typedef void (*smgrdounlinkall_hook_type)(SMgrRelation *rels,
+										  int nrels,
+										  bool isRedo,
+										  char *relstorages);
+extern PGDLLIMPORT smgrdounlinkall_hook_type smgrdounlinkall_hook;
+
 #endif   /* SMGR_H */