SQLite

  int pgsz,
  int bExtend,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Pointer to mapping */
){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xShmMap(id, iPage, pgsz, bExtend, pp);
}
int sqlite3OsMremap(
  sqlite3_file *id,               /* Database file handle */
  int flags,                      /* SQLITE_MREMAP_XXX flags */
  i64 iOff,                       /* Offset at which mapping(s) start */
  i64 nOld,                       /* Size of old mapping */
  i64 nNew,                       /* Size of requested mapping */
  void **pp                       /* IN/OUT: Pointer to mapped region */
){
  return id->pMethods->xMremap(id, flags, iOff, nOld, nNew, pp);
}

/*
** The next group of routines are convenience wrappers around the
** VFS methods.
*/
int sqlite3OsOpen(

#define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
int sqlite3OsSectorSize(sqlite3_file *id);
int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);
int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
void sqlite3OsShmBarrier(sqlite3_file *id);
int sqlite3OsShmUnmap(sqlite3_file *id, int);
int sqlite3OsMremap(sqlite3_file *id, int, i64, i64, i64, void **);


/* 
** Functions for accessing sqlite3_vfs methods 
*/
int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
int sqlite3OsDelete(sqlite3_vfs *, const char *, int);

#endif /* #ifndef SQLITE_OMIT_WAL */

/*
** Map, remap or unmap part of the database file.
*/
static int unixMremap(
  sqlite3_file *fd,               /* Main database file */
  int flags,                      /* Mask of SQLITE_MREMAP_XXX flags */
  sqlite3_int64 iOff,             /* Offset to start mapping at */
  sqlite3_int64 nOld,             /* Size of old mapping, or zero */
  sqlite3_int64 nNew,             /* Size of new mapping, or zero */
  void **ppMap                    /* IN/OUT: Old/new mappings */
){
  unixFile *p = (unixFile *)fd;   /* The underlying database file */
  int rc = SQLITE_OK;             /* Return code */
  void *pNew = 0;                 /* New mapping */
  i64 nRnd;                       /* nNew rounded up to 4096 */

  assert( iOff==0 );
  nRnd = (nNew+4095) & ~(i64)((1 << 12)-1);

  /* If the SQLITE_MREMAP_EXTEND flag is set, then the size of the requested 
  ** mapping (nNew bytes) may be greater than the size of the database file.
  ** If this is the case, extend the file on disk using ftruncate().  */
  assert( nNew>0 || (flags & SQLITE_MREMAP_EXTEND)==0 );
  if( flags & SQLITE_MREMAP_EXTEND ){
    struct stat statbuf;          /* Low-level file information */
    rc = osFstat(p->h, &statbuf);
    if( rc==SQLITE_OK && nNew>statbuf.st_size ){
      rc = robust_ftruncate(p->h, nNew);
    }
    if( rc!=SQLITE_OK ) return rc;
  }

#if defined(_GNU_SOURCE) && defined(__linux__)
  if( nRnd && nOld ){
    void *pOld = *ppMap;
    *ppMap = pNew = mremap(pOld, nOld, nNew, MREMAP_MAYMOVE);
    if( pNew==MAP_FAILED ){
      *ppMap = 0;
      return SQLITE_IOERR_MREMAP;
    }
    return SQLITE_OK;
  }
#endif

  if( nOld!=0 ){
    void *pOld = *ppMap;
    munmap(pOld, nOld);
  }

  if( nNew>0 ){
    int flags = PROT_READ;
    if( (p->ctrlFlags & UNIXFILE_RDONLY)==0 ) flags |= PROT_WRITE;

    pNew = mmap(0, nRnd, flags, MAP_SHARED, p->h, iOff);
    if( pNew==MAP_FAILED ){
      pNew = 0;
      rc = SQLITE_IOERR_MREMAP;
    }
  }

  *ppMap = pNew;
  return rc;
}

}

/*
** Unmap any memory mapping of the database file.
*/
static int pagerUnmap(Pager *pPager){
  if( pPager->pMap ){
    sqlite3OsMremap(pPager->fd, 0, 0, pPager->nMap, 0, &pPager->pMap);
    pPager->nMap = 0;
    pPager->nMapValid = 0;
  }
  return SQLITE_OK;
}

/*
** Create, or recreate, the memory mapping of the database file.
*/
static int pagerMap(Pager *pPager, int bExtend){
  int rc = SQLITE_OK;             /* Return code */
  Pgno nPg;                       /* Size of mapping to request in pages */
  i64 sz;                         /* Size of mapping to request in bytes */

  assert( pPager->pWal==0 && isOpen(pPager->fd) && pPager->tempFile==0 );
  assert( pPager->pMap==0 || pPager->nMap>0 );
  assert( pPager->eState>=1 );
  assert( pPager->nMmapOut==0 );
  assert( pPager->nMapLimit>0 );

  /* Figure out how large a mapping to request. Set variable sz to this 
  ** value in bytes. */
  nPg = (pPager->eState==1) ? pPager->dbSize : pPager->dbFileSize;
  sz = (i64)nPg * pPager->pageSize;
  if( sz>pPager->nMapLimit ) sz = pPager->nMapLimit;

  if( sz!=pPager->nMapValid ){
    int flags = (bExtend ? SQLITE_MREMAP_EXTEND : 0);
    rc = sqlite3OsMremap(pPager->fd, flags, 0, pPager->nMap, sz, &pPager->pMap);
    if( rc==SQLITE_OK ){
      assert( pPager->pMap!=0 );
      pPager->nMap = sz;
    }else{
      assert( pPager->pMap==0 );
      pPager->nMap = 0;
    }

    rc = pagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
  }

  /* Before the first write, give the VFS a hint of what the final
  ** file size will be.
  */
  assert( rc!=SQLITE_OK || isOpen(pPager->fd) );
  if( rc==SQLITE_OK 
   && (pList->pDirty ? pPager->dbSize : pList->pgno+1)>pPager->dbHintSize 
  ){
    sqlite3_int64 szFile = pPager->pageSize * (sqlite3_int64)pPager->dbSize;
    sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_SIZE_HINT, &szFile);
    pPager->dbHintSize = pPager->dbSize;

    if( pPager->nMmapOut==0 && pPager->nMapLimit>0 ){
      pPager->dbFileSize = pPager->dbSize;
      pagerMap(pPager, 1);
    }
  }

  while( rc==SQLITE_OK && pList ){
    Pgno pgno = pList->pgno;

    /* If there are dirty pages in the page cache with page numbers greater
    ** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to

  ** Otherwise, request the page from the PCache layer. */
  if( pPager->errCode!=SQLITE_OK ){
    rc = pPager->errCode;
  }else{

    if( bMmapOk ){
      if( pPager->pMap==0 || (pPager->bMapResize && pPager->nMmapOut==0) ){
        rc = pagerMap(pPager, 0);
      }
      if( rc==SQLITE_OK && pPager->nMap>=((i64)pgno * pPager->pageSize) ){
        if( pPager->eState>PAGER_READER ){
          (void)sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
        }
        if( pPg==0 ){
          rc = pagerAcquireMapPage(pPager, pgno, &pPg);

int sqlite3PagerReadFileheader(Pager*, int, unsigned char*);

/* Functions used to configure a Pager object. */
void sqlite3PagerSetBusyhandler(Pager*, int(*)(void *), void *);
int sqlite3PagerSetPagesize(Pager*, u32*, int);
int sqlite3PagerMaxPageCount(Pager*, int);
void sqlite3PagerSetCachesize(Pager*, int);
void sqlite3PagerSetMmapsize(Pager *, int);
void sqlite3PagerShrink(Pager*);
void sqlite3PagerSetSafetyLevel(Pager*,int,int,int);
int sqlite3PagerLockingMode(Pager *, int);
int sqlite3PagerSetJournalMode(Pager *, int);
int sqlite3PagerGetJournalMode(Pager*);
int sqlite3PagerOkToChangeJournalMode(Pager*);
i64 sqlite3PagerJournalSizeLimit(Pager *, i64);

#define SQLITE_IOERR_DIR_CLOSE         (SQLITE_IOERR | (17<<8))
#define SQLITE_IOERR_SHMOPEN           (SQLITE_IOERR | (18<<8))
#define SQLITE_IOERR_SHMSIZE           (SQLITE_IOERR | (19<<8))
#define SQLITE_IOERR_SHMLOCK           (SQLITE_IOERR | (20<<8))
#define SQLITE_IOERR_SHMMAP            (SQLITE_IOERR | (21<<8))
#define SQLITE_IOERR_SEEK              (SQLITE_IOERR | (22<<8))
#define SQLITE_IOERR_DELETE_NOENT      (SQLITE_IOERR | (23<<8))
#define SQLITE_IOERR_MREMAP            (SQLITE_IOERR | (24<<8))
#define SQLITE_LOCKED_SHAREDCACHE      (SQLITE_LOCKED |  (1<<8))
#define SQLITE_BUSY_RECOVERY           (SQLITE_BUSY   |  (1<<8))
#define SQLITE_CANTOPEN_NOTEMPDIR      (SQLITE_CANTOPEN | (1<<8))
#define SQLITE_CANTOPEN_ISDIR          (SQLITE_CANTOPEN | (2<<8))
#define SQLITE_CANTOPEN_FULLPATH       (SQLITE_CANTOPEN | (3<<8))
#define SQLITE_CORRUPT_VTAB            (SQLITE_CORRUPT | (1<<8))
#define SQLITE_READONLY_RECOVERY       (SQLITE_READONLY | (1<<8))

  int (*xDeviceCharacteristics)(sqlite3_file*);
  /* Methods above are valid for version 1 */
  int (*xShmMap)(sqlite3_file*, int iPg, int pgsz, int, void volatile**);
  int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
  void (*xShmBarrier)(sqlite3_file*);
  int (*xShmUnmap)(sqlite3_file*, int deleteFlag);
  /* Methods above are valid for version 2 */
  int (*xMremap)(sqlite3_file *fd, int flags,
      sqlite3_int64 iOff, sqlite3_int64 nOld, sqlite3_int64 nNew, void **ppMap);
  /* Methods above are valid for version 3 */
  /* Additional methods may be added in future releases */
};

#define SQLITE_MREMAP_EXTEND  0x0001        /* xMremap call may extend file */

/*
** CAPI3REF: Standard File Control Opcodes
**
** These integer constants are opcodes for the xFileControl method
** of the [sqlite3_io_methods] object and for the [sqlite3_file_control()]
** interface.