Add shared memory structure

Author: kovmir

pg_sqlwall.c

@@ -1,16 +1,94 @@
 #include "postgres.h"
 #include "fmgr.h"
+#include "nodes/nodes.h"
+#include "miscadmin.h"
+#include "storage/ipc.h"
+#include "storage/shmem.h"
+#include "storage/lwlock.h"
+#include "utils/builtins.h"
 
+/* Constants and Macros */
 PG_MODULE_MAGIC;
 
 /* Abost compilation against unsupported versions. */
 #if PG_VERSION_NUM < 130000
 #error "Unsupported PostgreSQL Version"
 #endif
 
+/* Is there a better size candidate? */
+#define DENY_LIST_SIZE 128
+/* CMD_NOTHING tells us about enum size as it is the last enum member. */
+#define CMD_TYPE_COUNT CMD_NOTHING+1
+
+typedef struct pgswUserPerm {
+	Oid userId;
+	/* Lists SQL command types the user is NOT allowed to run.
+	 * CmdType enum members are indexes for this array, i.e.
+	 * denyCmd[CMD_DELETE] = true to prohibit SQL DELETE statements. */
+	bool denyCmd[CMD_TYPE_COUNT];
+} pgswUserPerm;
+
+typedef struct pgswSharedState {
+	LWLock* lock;
+	pgswUserPerm denyList[DENY_LIST_SIZE];
+	int denyListSize;
+} pgswSharedState;
+
+/* Function Prototypes */
+void _PG_init(void);
+static void pgsw_shmem_request(void);
+static void pgsw_shmem_startup(void);
+
 Datum my_function(PG_FUNCTION_ARGS);
 PG_FUNCTION_INFO_V1(my_function);
 
+/* Global variables */
+static shmem_request_hook_type prev_shmem_request_hook = NULL;
+static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
+pgswSharedState *pgsw_shmem = NULL;
+
+void
+_PG_init(void)
+{
+	if(!process_shared_preload_libraries_in_progress)
+		elog(FATAL, "Please use shared_preload_libraries");
+
+	prev_shmem_request_hook = shmem_request_hook;
+	shmem_request_hook = pgsw_shmem_request;
+
+	prev_shmem_startup_hook = shmem_startup_hook;
+	shmem_startup_hook = pgsw_shmem_startup;
+}
+
+void
+pgsw_shmem_request(void)
+{
+	if(prev_shmem_request_hook)
+		prev_shmem_request_hook();
+
+	RequestAddinShmemSpace(MAXALIGN(sizeof(pgswSharedState)));
+	RequestNamedLWLockTranche("pg_sqlwall", 1);
+}
+
+void
+pgsw_shmem_startup(void)
+{
+	bool found;
+
+	if(prev_shmem_startup_hook)
+		prev_shmem_startup_hook();
+
+	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
+
+	pgsw_shmem = ShmemInitStruct("pg_sqlwall", sizeof(pgswSharedState), &found);
+	if(!found) {
+		pgsw_shmem->denyListSize = 0;
+		pgsw_shmem->lock = &(GetNamedLWLockTranche("pg_sqlwall"))->lock;
+	}
+
+	LWLockRelease(AddinShmemInitLock);
+}
+
 Datum
 my_function(PG_FUNCTION_ARGS)
 {