BackupWrite

The BackupWrite function writes a stream of data from a buffer to a specified file or directory. The data must be divided into substreams separated by WIN32_STREAM_ID structures. You use this function to restore a file or directory that has been backed up.

BOOL BackupWrite(
  HANDLE hFile,                   // handle to file or directory
  LPBYTE lpBuffer,                // write buffer
  DWORD nNumberOfBytesToWrite,    // number of bytes to write
  LPDWORD lpNumberOfBytesWritten, // number of bytes written
  BOOL bAbort,                    // termination type
  BOOL bProcessSecurity,          // process security
  LPVOID *lpContext               // context information
);

Parameters

hFile

[in] Handle to the file or directory being restored. The function writes data to this file. You obtain this handle by calling the CreateFile function.

The BackupWrite function fails if CreateFile was called with the flag FILE_FLAG_NO_BUFFERING. In this case, the GetLastError function returns the value ERROR_INVALID_PARAMETER.

lpBuffer

[in] Pointer to a buffer that the function writes data from.

nNumberOfBytesToWrite

[in] Specifies the length of the buffer. The buffer size must be greater than the size of a WIN32_STREAM_ID structure.

lpNumberOfBytesWritten

[out] Pointer to a variable that receives the number of bytes written.

bAbort

[in] Indicates whether you have finished using BackupWrite on the handle. While you are backing up the file, specify this parameter as FALSE. After you are done using BackupWrite, you must call BackupWrite one more time specifying TRUE for this parameter and passing the appropriate lpContext. lpContext must be passed when bAbort is TRUE; all other parameters are ignored.

bProcessSecurity

[in] Specifies whether the function will restore the access-control list (ACL) data for the file or directory.

If bProcessSecurity is TRUE, you need to have specified WRITE_OWNER and WRITE_DAC access when opening the file or directory handle. If the handle does not have those access rights, the operating system denies access to the ACL data, and ACL data restoration will not occur.

lpContext

[out] Pointer to a variable that receives a pointer to an internal data structure used by BackupWrite to maintain context information during a restore operation.

You must set the variable pointed to by lpContext to NULL before the first call to BackupWrite for the specified file or directory. The function allocates memory for the data structure, and then sets the variable to point to that structure. You must not change lpContext or the variable that it points to between calls to BackupWrite.

To release the memory used by the data structure, call BackupWrite with the bAbort parameter set to TRUE when the restore operation is complete.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero, indicating that an I/O error occurred. To get extended error information, call GetLastError.

Remarks

The BACKUP_LINK stream type lets you restore files with hard links.

Data obtained by the BackupRead function should only be used as input to the BackupWrite function.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Tape Backup Overview, Tape Backup Functions, BackupRead, BackupSeek, CreateFile, WIN32_STREAM_ID