NAME¶
gd_alter_frameoffset — modify the starting frame of fields in a dirfile
SYNOPSIS¶
#include <getdata.h>
int gd_alter_frameoffset(DIRFILE *dirfile,
off_t offset, int fragment_index, int
recode);
DESCRIPTION¶
The
gd_alter_frameoffset() function sets the frame offset of the format
specification fragment given by
fragment_index to
offset in the
dirfile(5) database specified by
dirfile. The frame offset of a
fragment indicate the frame number of the first sample of data stored in
binary files associated with
RAW fields defined in the specified
fragment. The frame offset of a fragment containing no
RAW fields is
ignored. The frame offset may not be negative.
The
dirfile argument must point to a valid DIRFILE object previously
created by a call to
gd_open(3).
In addition to being simply a valid fragment index,
fragment_index may
also be the special value
GD_ALL_FRAGMENTS, which indicates that the
frame offset of all fragments in the database should be changed.
If the
recode argument is non-zero, this call will shift the binary data
of affected
RAW fields to account for the change in frame offset. If
the new frame offset is larger than the old frame offset, this will result in
permanent deletion of data from the database. If the new frame offset is
smaller than the old frame offset, the binary file will be padded at the front
with zeroes. If
recode is zero, affected binary files are left
untouched.
RETURN VALUE¶
Upon successful completion,
gd_alter_frameoffset() returns zero. On
error, it returns -1 and sets the dirfile error to a non-zero error value.
Possible error values are:
- GD_E_ACCMODE
- The specified dirfile was opened read-only.
- GD_E_ALLOC
- The library was unable to allocate memory.
- GD_E_BAD_DIRFILE
- The supplied dirfile was invalid.
- GD_E_BAD_INDEX
- The supplied index was out of range.
- GD_E_PROTECTED
- The metadata of the given format specification fragment was protected from
change, or the binary data of the fragment was protected from change and
binary file shifting was requested.
- GD_E_RANGE
- The supplied offset was less than zero.
- GD_E_RAW_IO
- An I/O error occurred while attempting to shift a binary file.
- GD_E_UNCLEAN_DB
- An error occurred while moving the shifted file into place. As a result,
the database may be in an unclean state. See the NOTES section
below for recovery instructions. In this case, the dirfile will be flagged
as invalid, to prevent further database corruption. It should be
immediately closed.
- GD_E_UNKNOWN_ENCODING
- The encoding scheme of the fragment is unknown.
- GD_E_UNSUPPORTED
- The encoding scheme of the fragment does not support binary file
shifting.
The dirfile error may be retrieved by calling
gd_error(3). A descriptive
error string for the last error encountered can be obtained from a call to
gd_error_string(3).
NOTES¶
A binary file shift occurs out-of-place. As a result, sufficient space must be
present on the filesystem for the binary files of all
RAW fields in the
fragment both before and after translation. If all fragments are updated by
specifying
GD_ALL_FRAGMENTS, the shifting occurs one fragment at a
time.
An error code of
GD_E_UNCLEAN_DB indicates a system error occurred while
moving the shifted binary data into place or when deleting the old data. If
this happens, the database may be left in an unclean state. The caller should
check the filesystem directly to ascertain the state of the dirfile data
before continuing. For recovery instructions, see the file
/usr/share/doc/getdata/unclean_database_recovery.txt.
SEE ALSO¶
gd_open(3),
gd_error(3),
gd_error_string(3),
gd_frameoffset(3),
dirfile(5),
dirfile-format(5)