Refactoring the VFS-SHM methods used by WAL. This version compiles and

runs non-WAL test cases but crashes and burns on wal.test.

doc/vfs-shm.txt

@@ -78,14 +78,24 @@ during testing using an instrumented lock manager.
 
 (5)  No part of the wal-index will be read without holding either some
      kind of SHM lock or an EXCLUSIVE lock on the original database.
+     The original database is the file named in the 2nd parameter to
+     the xShmOpen method.
+
 (6)  A holder of a READ_FULL will never read any page of the database
      file that is contained anywhere in the wal-index.
+
 (7)  No part of the wal-index other than the header will be written nor
-     will the size of the wal-index grow without holding a WRITE.
+     will the size of the wal-index grow without holding a WRITE or
+     an EXCLUSIVE on the original database file.
+
 (8)  The wal-index header will not be written without holding one of
-     WRITE, CHECKPOINT, or RECOVER.
-(9)  A CHECKPOINT or RECOVER must be held in order to reset the last valid
-     frame counter in the header of the wal-index back to zero.
+     WRITE, CHECKPOINT, or RECOVER on the wal-index or an EXCLUSIVE on
+     the original database files.
+
+(9)  A CHECKPOINT or RECOVER must be held on the wal-index, or an
+     EXCLUSIVE on the original database file, in order to reset the 
+     last valid frame counter in the header of the wal-index back to zero.
+
 (10) A WRITE can only increase the last valid frame pointer in the header.
 
 The SQLite core will only ever send requests for UNLOCK, READ, WRITE,

src/os.c

@@ -98,6 +98,24 @@ int sqlite3OsSectorSize(sqlite3_file *id){
 int sqlite3OsDeviceCharacteristics(sqlite3_file *id){
   return id->pMethods->xDeviceCharacteristics(id);
 }
+int sqlite3OsShmOpen(sqlite3_file *id){
+  return id->pMethods->xShmOpen(id);
+}
+int sqlite3OsShmSize(sqlite3_file *id, int reqSize, int *pNewSize){
+  return id->pMethods->xShmSize(id, reqSize, pNewSize);
+}
+int sqlite3OsShmGet(sqlite3_file *id, int reqSize, int *pSize, void **pp){
+  return id->pMethods->xShmGet(id, reqSize, pSize, pp);
+}
+int sqlite3OsShmRelease(sqlite3_file *id){
+  return id->pMethods->xShmRelease(id);
+}
+int sqlite3OsShmLock(sqlite3_file *id, int desiredLock, int *pGotLock){
+  return id->pMethods->xShmLock(id, desiredLock, pGotLock);
+}
+int sqlite3OsShmClose(sqlite3_file *id, int deleteFlag){
+  return id->pMethods->xShmClose(id, deleteFlag);
+}
 
 /*
 ** The next group of routines are convenience wrappers around the

src/os.h

@@ -243,6 +243,12 @@ int sqlite3OsFileControl(sqlite3_file*,int,void*);
 #define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
 int sqlite3OsSectorSize(sqlite3_file *id);
 int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
+int sqlite3OsShmOpen(sqlite3_file *id);
+int sqlite3OsShmSize(sqlite3_file *id, int, int*);
+int sqlite3OsShmGet(sqlite3_file *id, int, int*, void**);
+int sqlite3OsShmRelease(sqlite3_file *id);
+int sqlite3OsShmLock(sqlite3_file *id, int, int*);
+int sqlite3OsShmClose(sqlite3_file *id, int);
 
 /* 
 ** Functions for accessing sqlite3_vfs methods