1 files changed, 14 insertions, 0 deletions
diff --git a/ext/misc/cksumvfs.c b/ext/misc/cksumvfs.c
index 0f6b00f43..6994dc776 100644
--- a/ext/misc/cksumvfs.c
+++ b/ext/misc/cksumvfs.c
@@ -579,6 +579,18 @@ static int cksmFileControl(sqlite3_file *pFile, int op, void *pArg){
   }else if( op==SQLITE_FCNTL_CKPT_START || op==SQLITE_FCNTL_CKPT_DONE ){
     p->inCkpt = op==SQLITE_FCNTL_CKPT_START;
     if( p->pPartner ) p->pPartner->inCkpt = p->inCkpt;
+  }else if( op==SQLITE_FCNTL_CKSM_FILE ){
+    /* This VFS needs to obtain a pointer to the corresponding database
+    ** file handle from within xOpen() calls to open wal files. To do this,
+    ** it uses the sqlite3_database_file_object() API to obtain a pointer
+    ** to the file-handle used by SQLite to access the db file. This is
+    ** fine if cksmvfs happens to be the top-level VFS, but not if there
+    ** are one or more wrapper VFS. To handle this case, this file-control
+    ** is used to extract the cksmvfs file-handle from any wrapper file 
+    ** handle.  */
+    sqlite3_file **ppFile = (sqlite3_file**)pArg;
+    *ppFile = (sqlite3_file*)p;
+    return SQLITE_OK;
   }
   rc = pFile->pMethods->xFileControl(pFile, op, pArg);
   if( rc==SQLITE_OK && op==SQLITE_FCNTL_VFSNAME ){
@@ -688,6 +700,8 @@ static int cksmOpen(
   if( rc ) goto cksm_open_done;
   if( flags & SQLITE_OPEN_WAL ){
     sqlite3_file *pDb = sqlite3_database_file_object(zName);
+    rc = pDb->pMethods->xFileControl(pDb, SQLITE_FCNTL_CKSM_FILE, (void*)&pDb);
+    assert( rc==SQLITE_OK );
     p->pPartner = (CksmFile*)pDb;
     assert( p->pPartner->pPartner==0 );
     p->pPartner->pPartner = p;