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gpfs_open_inodescan() Subroutine
Name
gpfs_open_inodescan() – Opens an inode scan of a file system or snapshot.
Library
GPFS Library (libgpfs.a for AIX, libgpfs.so for Linux)
Synopsis
#include
gpfs_iscan_t *gpfs_open_inodescan
(gpfs_fssnap_handle_t *fssnapHandle,
const gpfs_fssnap_id_t *prev_fssnapId,
gpfs_ino_t *maxIno);
Description
The gpfs_open_inodescan() subroutine opens a scan of the inodes in the file system or snapshot
identified by the fssnapHandle parameter. The scan traverses all user files, directories and links in the file
system or snapshot. The scan begins with the user file with the lowest inode number and returns the files
in increasing order. The gpfs_seek_inode() subroutine may be used to set the scan position to an
arbitrary inode. System files, such as the block allocation maps, are omitted from the scan. The file system
must be mounted to open an inode scan.
For an overview of using gpfs_open_inodescan() in a backup application, see “Using APIs to develop
backup applications” on page 24.
To generate a full backup, invoke gpfs_open_inodescan() with NULL for the prev_fssnapId parameter.
Repeated invocations of gpfs_next_inode() then return inode information about all existing user files,
directories and links, in inode number order.
To generate an incremental backup, invoke gpfs_open_inodescan() with the fssnapId that was obtained
from a fssnapHandle at the time the previous backup was created. The snapshot that was used for the
previous backup does not need to exist at the time the incremental backup is generated. That is, the
backup application needs to remember only the fssnapId of the previous backup; the snapshot itself can
be deleted as soon as the backup is completed.
For the incremental backup, any operation that changes the file’s mtime or ctime causes the file to be
included. Files with no changes to the file’s data or file attributes, other than a change to atime, are
omitted from the scan.
A full inode scan (prev_fssnapId set to NULL) does not return any inodes of nonexistent or deleted files,
but an incremental inode scan (prev_fssnapId not NULL) does return inodes for files that have been
deleted since the previous snapshot. The inodes of deleted files have a link count of zero.
If the snapshot indicated by prev_fssnapId is available, the caller may benefit from the extended read
subroutine, gpfs_ireadx(), which returns only the changed blocks within the files. Without the previous
snapshot, all blocks within the changed files are returned.
Once a full or incremental backup completes, the new_fssnapId must be saved in order to reuse it on a
subsequent incremental backup. This fssnapId must be provided to the gpfs_open_inodescan()
subroutine, as the prev_fssnapId input parameter.
Chapter 9. GPFS programming interfaces 331