}

/*
** Create or release a lock on shared memory.
*/
static int unixShmLock(
  sqlite3_shm *pSharedMem,   /* Pointer from unixShmOpen() */
  int lockType,              /* _RDLK, _WRLK, or _UNLK, possibly ORed _BLOCK */
  int ofst,                  /* Start of lock region */
  int nByte                  /* Size of lock region in bytes */
){
  struct unixShm *p = (struct unixShm*)pSharedMem;
  struct flock f;
  int op;
  int rc;
  
  f.l_whence = SEEK_SET;
  f.l_start = ofst;
  f.l_len = nByte;
  switch( lockType & 0x07 ){
    case SQLITE_SHM_RDLK:  f.l_type = F_RDLCK;   break;
    case SQLITE_SHM_WRLK:  f.l_type = F_WRLCK;   break;
    case SQLITE_SHM_UNLK:  f.l_type = F_UNLCK;   break;
  }
  op = (lockType & 0x08)!=0 ? F_SETLKW : F_SETLK;
  rc = fcntl(p->fd.h, op, &f);
  return (rc==0) ? SQLITE_OK : SQLITE_BUSY;
}

/*
** Delete a shared-memory segment from the system.
*/
static int unixShmDelete(sqlite3_vfs *pVfs, const char *zName){
  return pVfs->xDelete(pVfs, zName, 0);

}

/*
** Create or release a lock on shared memory.
*/
static int unixShmLock(
  sqlite3_shm *pSharedMem,   /* Pointer from unixShmOpen() */
  int desiredLock,           /* The locking state desired */
  int *pGotLock,             /* The locking state actually obtained */
  int shouldBlock            /* Block for the lock if true and possible */
){
  return SQLITE_OK;















}

/*
** Delete a shared-memory segment from the system.
*/
static int unixShmDelete(sqlite3_vfs *pVfs, const char *zName){
  return pVfs->xDelete(pVfs, zName, 0);

  ** definition.  Those that follow are added in version 2 or later
  */
  int (*xShmOpen)(sqlite3_vfs*, const char *zName, sqlite3_shm**);
  int (*xShmSize)(sqlite3_shm*, int reqSize, int *pNewSize, char**);
  int (*xShmRelease)(sqlite3_shm*);
  int (*xShmPush)(sqlite3_shm*);
  int (*xShmPull)(sqlite3_shm*);
  int (*xShmLock)(sqlite3_shm*, int lockType, int ofst, int nByte);
  int (*xShmClose)(sqlite3_shm*);
  int (*xShmDelete)(sqlite3_vfs*, const char *zName);
  int (*xRename)(sqlite3_vfs*, const char *zOld, const char *zNew, int dirSync);
  int (*xCurrentTimeInt64)(sqlite3_vfs*, sqlite3_int64*);
  /*
  ** The methods above are in versions 1 and 2 of the sqlite_vfs object.
  ** New fields may be appended in figure versions.  The iVersion
................................................................................
#define SQLITE_ACCESS_EXISTS    0
#define SQLITE_ACCESS_READWRITE 1
#define SQLITE_ACCESS_READ      2

/*
** CAPI3REF: Flags for the xShmLock VFS method
**
** These integer constants can be used as the second parameter to
** the xShmLock method of an [sqlite3_vfs] object.  They determine
** the specific locking action.  Exactly one of the first three
** values must be used ini the lockType parameter.  The fourth
** value (SQLITE_SHM_BLOCK) can optionally be ORed into the lockType
** parameter to cause the thread to block until the lock becomes
** available.
*/

#define SQLITE_SHM_RDLK   0x01

#define SQLITE_SHM_WRLK   0x02
#define SQLITE_SHM_UNLK   0x04
#define SQLITE_SHM_BLOCK  0x08



/*
** CAPI3REF: Initialize The SQLite Library
**
** ^The sqlite3_initialize() routine initializes the
** SQLite library.  ^The sqlite3_shutdown() routine
** deallocates any resources that were allocated by sqlite3_initialize().

  ** definition.  Those that follow are added in version 2 or later
  */
  int (*xShmOpen)(sqlite3_vfs*, const char *zName, sqlite3_shm**);
  int (*xShmSize)(sqlite3_shm*, int reqSize, int *pNewSize, char**);
  int (*xShmRelease)(sqlite3_shm*);
  int (*xShmPush)(sqlite3_shm*);
  int (*xShmPull)(sqlite3_shm*);
  int (*xShmLock)(sqlite3_shm*, int desiredLock, int *gotLock, int shouldBlock);
  int (*xShmClose)(sqlite3_shm*);
  int (*xShmDelete)(sqlite3_vfs*, const char *zName);
  int (*xRename)(sqlite3_vfs*, const char *zOld, const char *zNew, int dirSync);
  int (*xCurrentTimeInt64)(sqlite3_vfs*, sqlite3_int64*);
  /*
  ** The methods above are in versions 1 and 2 of the sqlite_vfs object.
  ** New fields may be appended in figure versions.  The iVersion
................................................................................
#define SQLITE_ACCESS_EXISTS    0
#define SQLITE_ACCESS_READWRITE 1
#define SQLITE_ACCESS_READ      2

/*
** CAPI3REF: Flags for the xShmLock VFS method
**
** These integer constants define the various locking states that
** an sqlite3_shm object can be in.  The SQLITE_SHM_QUERY integer
** is not a valid data - it is a constant pasted to the 
** sqlite3_vfs.xShmLock() method for querying the current lock
** state.


*/
#define SQLITE_SHM_UNLOCK       0
#define SQLITE_SHM_READ_PREFIX  1
#define SQLITE_SHM_READ_FULL    2
#define SQLITE_SHM_WRITE        3
#define SQLITE_SHM_PENDING      4
#define SQLITE_SHM_CHECKPOINT   5
#define SQLITE_SHM_RECOVER      6
#define SQLITE_SHM_QUERY        (-1)

/*
** CAPI3REF: Initialize The SQLite Library
**
** ^The sqlite3_initialize() routine initializes the
** SQLite library.  ^The sqlite3_shutdown() routine
** deallocates any resources that were allocated by sqlite3_initialize().