BackupRead
The BackupRead
function reads data associated with a specified file or directory into a
buffer. You use this function to back up a file or directory.
BOOL BackupRead(
|
HANDLE hFile, |
// handle to file
or directory |
|
LPBYTE lpBuffer, |
// pointer to
buffer to read to |
|
DWORD nNumberOfBytesToRead, |
// number of bytes
to read |
|
LPDWORD lpNumberOfBytesRead, |
// pointer to
variable to receive number of bytes read |
|
BOOL bAbort, |
// termination type
|
|
BOOL bProcessSecurity, |
// process security
flag |
|
LPVOID *lpContext |
// pointer to
pointer to internal context information |
|
); |
|
Parameters
hFile
Handle to the
file or directory being backed up. The function reads data associated with this
file. You obtain this handle by calling the CreateFile function.
The BackupRead
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
Pointer to a
buffer that the function writes data to.
nNumberOfBytesToRead
Specifies the
length of the buffer. The buffer size
must be greater than the size of a WIN32_STREAM_ID structure.
lpNumberOfBytesRead
Pointer to a
variable that, when the function returns, contains the number of bytes read.
If the
function return value is TRUE, and the variable pointed to by lpNumberOfBytesRead
is zero, then all the data associated with the file handle has been read.
bAbort
Indicates
whether BackupRead terminated abnormally. If this value is TRUE, the
operation terminates abnormally and all buffers are deallocated.
bProcessSecurity
Indicates
whether the function will restore the access-control list (ACL) data for the
file or directory.
If bProcessSecurity
is TRUE, the ACL data will be backed up.
lpContext
Pointer to a
variable that receives and holds a pointer to an internal data structure used
by BackupRead to maintain context information during a backup
operation.
You must set
the variable pointed to by lpContext to NULL before the first call to BackupRead
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 BackupRead.
To release
the memory used by the data structure, call BackupRead with the bAbort
parameter set to TRUE when the backup 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
BackupRead processes all of the data pertaining to an opened
object as a series of discrete byte streams. Each stream is preceded by a
32-bit aligned WIN32_STREAM_ID structure.
Streams must
be processed in the same order in which they were written to the tape. This
ordering enables applications to compare the data backed up against the data on
the source device. The data returned by BackupRead is to be used only as
input to the BackupWrite function. This data is returned as one large
data stream divided into substreams. The substreams are separated by WIN32_STREAM_ID
headers.
If an error
occurs while BackupRead is reading, the calling process can skip the bad
data by calling the BackupSeek function.
See Also