Index: src/dbpage.c
==================================================================
--- src/dbpage.c
+++ src/dbpage.c
@@ -26,11 +26,17 @@
 ** schema for the database file that is to be read.  The default schema is
 ** "main".
 **
 ** The data field of sqlite_dbpage table can be updated.  The new
 ** value must be a BLOB which is the correct page size, otherwise the
-** update fails.  Rows may not be deleted or inserted.
+** update fails.  INSERT operations also work, and operate as if they
+** where REPLACE.  The size of the database can be extended by INSERT-ing
+** new pages on the end.
+**
+** Rows may not be deleted.  However, doing an INSERT to page number N
+** with NULL page data causes the N-th page and all subsequent pages to be
+** deleted and the database to be truncated.
 */
 
 #include "sqliteInt.h"   /* Requires access to internal data structures */
 #if (defined(SQLITE_ENABLE_DBPAGE_VTAB) || defined(SQLITE_TEST)) \
     && !defined(SQLITE_OMIT_VIRTUALTABLE)
@@ -49,17 +55,18 @@
 };
 
 struct DbpageTable {
   sqlite3_vtab base;              /* Base class.  Must be first */
   sqlite3 *db;                    /* The database */
+  int nTrunc;                     /* Entries in aTrunc[] */
+  Pgno *aTrunc;                   /* Truncation size for each database */
 };
 
 /* Columns */
 #define DBPAGE_COLUMN_PGNO    0
 #define DBPAGE_COLUMN_DATA    1
 #define DBPAGE_COLUMN_SCHEMA  2
-
 
 
 /*
 ** Connect to or create a dbpagevfs virtual table.
 */
@@ -98,10 +105,12 @@
 
 /*
 ** Disconnect from or destroy a dbpagevfs virtual table.
 */
 static int dbpageDisconnect(sqlite3_vtab *pVtab){
+  DbpageTable *pTab = (DbpageTable *)pVtab;
+  sqlite3_free(pTab->aTrunc);
   sqlite3_free(pVtab);
   return SQLITE_OK;
 }
 
 /*
@@ -323,10 +332,11 @@
   char *zErr = 0;
   int iDb;
   Btree *pBt;
   Pager *pPager;
   int szPage;
+  int isInsert;
 
   (void)pRowid;
   if( pTab->db->flags & SQLITE_Defensive ){
     zErr = "read-only";
     goto update_fail;
@@ -335,22 +345,24 @@
     zErr = "cannot delete";
     goto update_fail;
   }
   if( sqlite3_value_type(argv[0])==SQLITE_NULL ){
     pgno = (Pgno)sqlite3_value_int(argv[2]);
+    isInsert = 1;
   }else{
     pgno = sqlite3_value_int(argv[0]);
     if( (Pgno)sqlite3_value_int(argv[1])!=pgno ){
       zErr = "cannot insert";
       goto update_fail;
     }
+    isInsert = 0;
   }
   if( sqlite3_value_type(argv[4])==SQLITE_NULL ){
     iDb = 0;
   }else{
     const char *zSchema = (const char*)sqlite3_value_text(argv[4]);
-    iDb = zSchema ? sqlite3FindDbName(pTab->db, zSchema) : -1;
+    iDb = sqlite3FindDbName(pTab->db, zSchema);
     if( iDb<0 ){
       zErr = "no such schema";
       goto update_fail;
     }
   }
@@ -361,22 +373,35 @@
   }
   szPage = sqlite3BtreeGetPageSize(pBt);
   if( sqlite3_value_type(argv[3])!=SQLITE_BLOB 
    || sqlite3_value_bytes(argv[3])!=szPage
   ){
-    zErr = "bad page value";
-    goto update_fail;
+    if( sqlite3_value_type(argv[3])==SQLITE_NULL && isInsert ){
+      if( iDb>=pTab->nTrunc ){
+        testcase( pTab->aTrunc!=0 );
+        pTab->aTrunc = sqlite3_realloc(pTab->aTrunc, (iDb+1)*sizeof(Pgno));
+        if( pTab->aTrunc ){
+          int j;
+          for(j=pTab->nTrunc; j<iDb; j++) pTab->aTrunc[j] = 0;
+          pTab->nTrunc = iDb+1;
+        }else{
+          return SQLITE_NOMEM;
+        }
+      }
+      pTab->aTrunc[iDb] = pgno;
+    }else{
+      zErr = "bad page value";
+      goto update_fail;
+    }
   }
   pPager = sqlite3BtreePager(pBt);
   rc = sqlite3PagerGet(pPager, pgno, (DbPage**)&pDbPage, 0);
   if( rc==SQLITE_OK ){
     const void *pData = sqlite3_value_blob(argv[3]);
-    assert( pData!=0 || pTab->db->mallocFailed );
-    if( pData
-     && (rc = sqlite3PagerWrite(pDbPage))==SQLITE_OK
-    ){
-      memcpy(sqlite3PagerGetData(pDbPage), pData, szPage);
+    if( (rc = sqlite3PagerWrite(pDbPage))==SQLITE_OK && pData ){
+      unsigned char *aPage = sqlite3PagerGetData(pDbPage);
+      memcpy(aPage, pData, szPage);
     }
   }
   sqlite3PagerUnref(pDbPage);
   return rc;
 
@@ -395,10 +420,30 @@
   sqlite3 *db = pTab->db;
   int i;
   for(i=0; i<db->nDb; i++){
     Btree *pBt = db->aDb[i].pBt;
     if( pBt ) (void)sqlite3BtreeBeginTrans(pBt, 1, 0);
+  }
+  if( pTab->nTrunc>0 ){
+    memset(pTab->aTrunc, 0, sizeof(pTab->aTrunc[0])*pTab->nTrunc);
+  }
+  return SQLITE_OK;
+}
+
+/* Invoke sqlite3PagerTruncate() as necessary, just prior to COMMIT
+*/
+static int dbpageSync(sqlite3_vtab *pVtab){
+  int iDb;
+  DbpageTable *pTab = (DbpageTable *)pVtab;
+
+  for(iDb=0; iDb<pTab->nTrunc; iDb++){
+    if( pTab->aTrunc[iDb]>0 ){
+      Btree *pBt = pTab->db->aDb[iDb].pBt;
+      Pager *pPager = sqlite3BtreePager(pBt);
+      sqlite3PagerTruncateImage(pPager, pTab->aTrunc[iDb]);
+      pTab->aTrunc[iDb] = 0;
+    }
   }
   return SQLITE_OK;
 }
 
 
@@ -420,11 +465,11 @@
     dbpageEof,                    /* xEof - check for end of scan */
     dbpageColumn,                 /* xColumn - read data */
     dbpageRowid,                  /* xRowid - read data */
     dbpageUpdate,                 /* xUpdate */
     dbpageBegin,                  /* xBegin */
-    0,                            /* xSync */
+    dbpageSync,                   /* xSync */
     0,                            /* xCommit */
     0,                            /* xRollback */
     0,                            /* xFindMethod */
     0,                            /* xRename */
     0,                            /* xSavepoint */