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gpfs_ireadx() Subroutine
Name
gpfs_ireadx() - Performs block level incremental read of a file within an incremental inode scan.
Library
GPFS Library (libgpfs.a for AIX, libgpfs.so for Linux)
Synopsis
#include
gpfs_off64_t gpfs_ireadx(gpfs_ifile_t *ifile,
gpfs_iscan_t *iscan,
void *buffer,
int bufferSize,
gpfs_off64_t *offset,
gpfs_off64_t termOffset,
int *hole);
Description
The gpfs_ireadx() subroutine performs a block level incremental read on a file opened by gpfs_iopen()
within a given incremental scan opened using gpfs_open_inodescan().
For an overview of using gpfs_ireadx() in a backup application, see “Using APIs to develop backup
applications” on page 24.
The gpfs_ireadx() subroutines returns the data that has changed since the prev_fssnapId specified for
the inode scan. The file is scanned starting at offset and terminating at termOffset, looking for changed
data. Once changed data is located, the offset parameter is set to its location, the new data is returned in
the buffer provided, and the amount of data returned is the subroutine’s value.
If the change to the data is that it has been deleted (that is, the file has been truncated), no data is
returned, but the hole parameter is returned with a value of 1, and the size of the hole is returned as the
subroutine’s value. The returned size of the hole may exceed the bufferSize provided. If no changed data
was found before reaching the termOffset or the end-of-file, then the gpfs_ireadx() subroutine return
value is 0.
Block level incremental backups are available only if the previous snapshot was not deleted. If it was
deleted, gpfs_ireadx() may still be used, but it returns all of the file’s data, operating like the standard
gpfs_iread() subroutine. However, the gpfs_ireadx() subroutine will still identify sparse files and explicitly
return information on holes in the files, rather than returning the NULL data.
Notes:
1. Compile any program that uses this subroutine with the -lgpfs flag from the following library:
v libgpfs.a for AIX
v libgpfs.so for Linux
Parameters
ifile Pointer to gpfs_ifile_t returned from gpfs_iopen().
iscan Pointer to gpfs_iscan_t from gpfs_open_inodescan().
buffer Pointer to buffer for returned data, or NULL to query the next increment to be read.
bufferSize Size of buffer for returned data.
Chapter 9. GPFS programming interfaces 325