SQLite

**   can be used on file systems that do not offer any reliable file locking
** NO locking means that no locking will be attempted, this is only used for
**   read-only file systems currently
** UNSUPPORTED means that no locking will be attempted, this is only used for
**   file systems that are known to be unsupported
*/
typedef enum {
        posixLockingStyle = 0,       /* standard posix-advisory locks */
        afpLockingStyle,             /* use afp locks */
        flockLockingStyle,           /* use flock() */
        dotlockLockingStyle,         /* use <file>.lock files */
        noLockingStyle,              /* useful for read-only file system */
        unsupportedLockingStyle      /* indicates unsupported file system */
} sqlite3LockingStyle;
#endif /* SQLITE_ENABLE_LOCKING_STYLE */

/*
** Helper functions to obtain and relinquish the global mutex.
*/
static void enterMutex(){

){

#ifdef SQLITE_FIXED_LOCKING_STYLE
  return (sqlite3LockingStyle)SQLITE_FIXED_LOCKING_STYLE;
#else
  struct statfs fsInfo;

  if (statfs(filePath, &fsInfo) == -1)
    return sqlite3TestLockingStyle(filePath, fd);
  
  if (fsInfo.f_flags & MNT_RDONLY)
    return noLockingStyle;
  
  if( (!strcmp(fsInfo.f_fstypename, "hfs")) ||
    (!strcmp(fsInfo.f_fstypename, "ufs")) )
                return posixLockingStyle;
  
  if(!strcmp(fsInfo.f_fstypename, "afpfs"))
    return afpLockingStyle;
  
  if(!strcmp(fsInfo.f_fstypename, "nfs")) 
    return sqlite3TestLockingStyle(filePath, fd);
  
  if(!strcmp(fsInfo.f_fstypename, "smbfs"))
    return flockLockingStyle;
  
  if(!strcmp(fsInfo.f_fstypename, "msdos"))
    return dotlockLockingStyle;
  
  if(!strcmp(fsInfo.f_fstypename, "webdav"))
    return unsupportedLockingStyle;
  
  return sqlite3TestLockingStyle(filePath, fd);  
#endif /* SQLITE_FIXED_LOCKING_STYLE */
}

#endif /* SQLITE_ENABLE_LOCKING_STYLE */

/*

#pragma mark AFP Support

/*
 ** The afpLockingContext structure contains all afp lock specific state
 */
typedef struct afpLockingContext afpLockingContext;
struct afpLockingContext {
  unsigned long long sharedLockByte;
  char *filePath;
};

struct ByteRangeLockPB2
{
  unsigned long long offset;        /* offset to first byte to lock */
  unsigned long long length;        /* nbr of bytes to lock */
  unsigned long long retRangeStart; /* nbr of 1st byte locked if successful */

  OSTRACE3("TEST WR-LOCK %d %d\n", pFile->h, r);
  
  return r;
}

/* AFP-style locking following the behavior of unixLock, see the unixLock 
** function comments for details of lock management. */
static int afpUnixLock(sqlite3_file *id, int locktype)
{
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;
  afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
  int gotPendingLock = 0;
  
  assert( pFile );
  OSTRACE5("LOCK    %d %s was %s pid=%d\n", pFile->h,
         locktypeName(locktype), locktypeName(pFile->locktype), getpid());  

  /* If there is already a lock of this type or more restrictive on the
    ** unixFile, do nothing. Don't use the afp_end_lock: exit path, as
    ** enterMutex() hasn't been called yet.
    */
  if( pFile->locktype>=locktype ){
    OSTRACE3("LOCK    %d %s ok (already held)\n", pFile->h,
           locktypeName(locktype));
    return SQLITE_OK;
  }

  /* Make sure the locking sequence is correct
    */
  assert( pFile->locktype!=NO_LOCK || locktype==SHARED_LOCK );
  assert( locktype!=PENDING_LOCK );
  assert( locktype!=RESERVED_LOCK || pFile->locktype==SHARED_LOCK );
  
  /* This mutex is needed because pFile->pLock is shared across threads
    */
  enterMutex();

  /* Make sure the current thread owns the pFile.
    */
  rc = transferOwnership(pFile);
  if( rc!=SQLITE_OK ){
    leaveMutex();
    return rc;
  }
    
  /* A PENDING lock is needed before acquiring a SHARED lock and before
    ** acquiring an EXCLUSIVE lock.  For the SHARED lock, the PENDING will
    ** be released.
    */
  if( locktype==SHARED_LOCK 
      || (locktype==EXCLUSIVE_LOCK && pFile->locktype<PENDING_LOCK)
      ){
    int failed = _AFPFSSetLock(context->filePath, pFile->h, 
      PENDING_BYTE, 1, 1);
    if (failed) {
      rc = SQLITE_BUSY;
      goto afp_end_lock;
    }
  }
  
  /* If control gets to this point, then actually go ahead and make
    ** operating system calls for the specified lock.
    */
  if( locktype==SHARED_LOCK ){
    int lk, failed;
    int tries = 0;
    
    /* Now get the read-lock */
    /* note that the quality of the randomness doesn't matter that much */
    lk = random(); 

  if( rc==SQLITE_OK ){
    pFile->locktype = locktype;
  }else if( locktype==EXCLUSIVE_LOCK ){
    pFile->locktype = PENDING_LOCK;
  }
  
afp_end_lock:
    leaveMutex();
  OSTRACE4("LOCK    %d %s %s\n", pFile->h, locktypeName(locktype), 
         rc==SQLITE_OK ? "ok" : "failed");
  return rc;
}

/*
 ** Lower the locking level on file descriptor pFile to locktype.  locktype
 ** must be either NO_LOCK or SHARED_LOCK.
 **
 ** If the locking level of the file descriptor is already at or below
 ** the requested locking level, this routine is a no-op.
 */
static int afpUnixUnlock(sqlite3_file *id, int locktype) {
  struct flock lock;
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;
  afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;

  assert( pFile );

  if (rc == SQLITE_OK)
    pFile->locktype = locktype;
  leaveMutex();
  return rc;
}

/*
 ** Close a file & cleanup AFP specific locking context 
 */
static int afpUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;

  if( !pFile ) return SQLITE_OK;
  afpUnixUnlock(id, NO_LOCK);
  /* free the AFP locking structure */
  if (pFile->lockingContext != NULL) {
    if (((afpLockingContext *)pFile->lockingContext)->filePath != NULL)
      sqlite3_free(((afpLockingContext*)pFile->lockingContext)->filePath);
    sqlite3_free(pFile->lockingContext);
  }

  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();
  close(pFile->h);
  leaveMutex();
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  memset(pFile, 0, sizeof(unixFile));
  return SQLITE_OK;
}


#pragma mark flock() style locking

/*
 ** The flockLockingContext is not used
 */
typedef void flockLockingContext;

static int flockUnixCheckReservedLock(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if (pFile->locktype == RESERVED_LOCK) {
    return 1; /* already have a reserved lock */
  } else {
    /* attempt to get the lock */
    int rc = flock(pFile->h, LOCK_EX | LOCK_NB);

  else {
    pFile->locktype = NO_LOCK;
    return SQLITE_OK;
  }
}

/*
 ** Close a file.
 */
static int flockUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if( !pFile ) return SQLITE_OK;
  flockUnixUnlock(id, NO_LOCK);
  
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;

  enterMutex();
  close(pFile->h);  
  leaveMutex();
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  memset(pFile, 0, sizeof(unixFile));
  return SQLITE_OK;
}

#pragma mark Old-School .lock file based locking

/*
 ** The dotlockLockingContext structure contains all dotlock (.lock) lock
 ** specific state
 */
typedef struct dotlockLockingContext dotlockLockingContext;
struct dotlockLockingContext {
  char *lockPath;
};


static int dotlockUnixCheckReservedLock(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 
    (dotlockLockingContext *) pFile->lockingContext;
  

  if (pFile->locktype == RESERVED_LOCK) {
    return 1; /* already have a reserved lock */
  } else {
    struct stat statBuf;
    if (lstat(context->lockPath,&statBuf) == 0)
      /* file exists, someone else has the lock */
      return 1;
    else
      /* file does not exist, we could have it if we want it */
      return 0;

  }
}

static int dotlockUnixLock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 


    (dotlockLockingContext *) pFile->lockingContext;
  
  /* if we already have a lock, it is exclusive.  
  ** Just adjust level and punt on outta here. */
  if (pFile->locktype > NO_LOCK) {
    pFile->locktype = locktype;
    
    /* Always update the timestamp on the old file */
    utimes(context->lockPath,NULL);
    return SQLITE_OK;
  }
  
  /* check to see if lock file already exists */
  struct stat statBuf;
  if (lstat(context->lockPath,&statBuf) == 0){
    return SQLITE_BUSY; /* it does, busy */
  }
  
  /* grab an exclusive lock */
  int fd = open(context->lockPath,O_RDONLY|O_CREAT|O_EXCL,0600);
  if (fd < 0) {
    /* failed to open/create the file, someone else may have stolen the lock */
    return SQLITE_BUSY; 
  }
  close(fd);
  
  /* got it, set the type and return ok */
  pFile->locktype = locktype;
  return SQLITE_OK;
}

static int dotlockUnixUnlock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 

    (dotlockLockingContext *) pFile->lockingContext;
  
  assert( locktype<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->locktype==locktype ){
    return SQLITE_OK;
  }

 ** Close a file.
 */
static int dotlockUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if( !pFile ) return SQLITE_OK;
  dotlockUnixUnlock(id, NO_LOCK);
  /* free the dotlock locking structure */
  if (pFile->lockingContext != NULL) {
    if (((dotlockLockingContext *)pFile->lockingContext)->lockPath != NULL)
      sqlite3_free( ( (dotlockLockingContext *)
        pFile->lockingContext)->lockPath);
    sqlite3_free(pFile->lockingContext);
  }
  
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();  
  close(pFile->h);
  leaveMutex();
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  memset(pFile, 0, sizeof(unixFile));
  return SQLITE_OK;
}


#pragma mark No locking

/*
 ** The nolockLockingContext is void
 */
typedef void nolockLockingContext;

static int nolockUnixCheckReservedLock(sqlite3_file *id) {
  return 0;
}

static int nolockUnixLock(sqlite3_file *id, int locktype) {
  return SQLITE_OK;
}

static int nolockUnixUnlock(sqlite3_file *id, int locktype) {
  return SQLITE_OK;
}

/*
 ** Close a file.
 */
static int nolockUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if( !pFile ) return SQLITE_OK;
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();
  close(pFile->h);
  leaveMutex();
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  memset(pFile, 0, sizeof(unixFile));
  return SQLITE_OK;
}

#endif /* SQLITE_ENABLE_LOCKING_STYLE */

  unixFileControl,
  unixSectorSize,
  unixDeviceCharacteristics
};

/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix with dotlock style file locking.
*/
static const sqlite3_io_methods sqlite3NolockLockingUnixIoMethod = {
  1,                        /* iVersion */
  nolockUnixClose,
  unixRead,
  unixWrite,
  unixTruncate,

  int rc;

#ifdef FD_CLOEXEC
  fcntl(h, F_SETFD, fcntl(h, F_GETFD, 0) | FD_CLOEXEC);
#endif

  lockingStyle = sqlite3DetectLockingStyle(zFilename, h);
  if ( lockingStyle == posixLockingStyle ) {
      
    enterMutex();
    rc = findLockInfo(h, &pNew->pLock, &pNew->pOpen);
    leaveMutex();
    if( rc ){
      if( dirfd>=0 ) close(dirfd);
      close(h);
      return SQLITE_NOMEM;

  pNew->dirfd = dirfd;
  SET_THREADID(pNew);
    
  switch(lockingStyle) {
    case afpLockingStyle: {
      /* afp locking uses the file path so it needs to be included in
      ** the afpLockingContext */
      int nFilename;
      pNew->pMethod = &sqlite3AFPLockingUnixIoMethod;
      pNew->lockingContext = 
        sqlite3_malloc(sizeof(afpLockingContext));
      nFilename = strlen(zFilename)+1;



      ((afpLockingContext *)pNew->lockingContext)->filePath = 


        sqlite3_malloc(nFilename);
      memcpy(((afpLockingContext *)pNew->lockingContext)->filePath, 
             zFilename, nFilename);
      srandomdev();
      break;
    }
    case flockLockingStyle:
      /* flock locking doesn't need additional lockingContext information */
      pNew->pMethod = &sqlite3FlockLockingUnixIoMethod;
      break;
    case dotlockLockingStyle: {
      /* dotlock locking uses the file path so it needs to be included in
       ** the dotlockLockingContext */

      int nFilename;

      pNew->pMethod = &sqlite3DotlockLockingUnixIoMethod;
      pNew->lockingContext = sqlite3_malloc(
        sizeof(dotlockLockingContext));
      nFilename = strlen(zFilename) + 6;
      ((dotlockLockingContext *)pNew->lockingContext)->lockPath = 
          sqlite3_malloc( nFilename );






      sqlite3_snprintf(nFilename, 
              ((dotlockLockingContext *)pNew->lockingContext)->lockPath, 
              "%s.lock", zFilename);
      break;
    }
    case posixLockingStyle:
      /* posix locking doesn't need additional lockingContext information */
      pNew->pMethod = &sqlite3UnixIoMethod;
      break;
    case noLockingStyle: