table of contents
gd_alter_frameoffset — modify the starting frame of fields in a Dirfile
int gd_alter_frameoffset(DIRFILE *dirfile, off_t offset, int fragment_index, int recode);
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. The I/O pointer of all affected RAW fields is reset to the beginning-of-frame.
If recode is zero, affected binary files are left untouched.
Upon successful completion, gd_alter_frameoffset() returns zero. On error, it returns a negative-valued error code. Possible error codes are:
- The specified dirfile was opened read-only.
- The library was unable to allocate memory.
- The supplied dirfile was invalid.
- The supplied index was out of range.
- An I/O error occurred while attempting to shift a binary file.
- 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.
- The supplied offset was less than zero.
- 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.
- The encoding scheme of the fragment is unknown.
- The encoding scheme of the fragment does not support binary file shifting.
The error code is also stored in the DIRFILE object and may be retrieved after this function returns by calling gd_error(3). A descriptive error string for the error may be obtained by calling gd_error_string(3).
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.
The function dirfile_alter_frameoffset() appeared in GetData-0.5.0.
In GetData-0.7.0, this function was renamed to gd_alter_frameoffset().
in GetData-0.10.0, the error return from this function changed from -1 to a negative-valued error code.
gd_open(3), gd_error(3), gd_error_string(3), gd_frameoffset(3), dirfile(5), dirfile-format(5)
|25 December 2016||Version 0.10.0|