.\" gd_alter_frameoffset.3.  The gd_alter_frameoffset man page.
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.TH gd_alter_frameoffset 3 "16 October 2014" "Version 0.9.0" "GETDATA"
.SH NAME
gd_alter_frameoffset \(em modify the starting frame of fields in a dirfile
.SH SYNOPSIS
.B #include <getdata.h>
.HP
.nh
.ad l
.BI "int gd_alter_frameoffset(DIRFILE *" dirfile ", off_t " offset ,
.BI "int " fragment_index ", int " recode );
.hy
.ad n
.SH DESCRIPTION
The
.BR gd_alter_frameoffset ()
function sets the frame offset of the format specification fragment given by
.I fragment_index
to
.I offset
in the dirfile(5) database specified by
.IR dirfile .
The frame offset of a fragment indicate the frame number of the first sample
of data stored in binary files associated with
.B RAW
fields defined in the specified fragment.  The frame offset of a fragment
containing no
.B RAW
fields is ignored.  The frame offset may not be negative.

The
.I dirfile
argument must point to a valid DIRFILE object previously created by a call to
.BR gd_open (3).

In addition to being simply a valid fragment index,
.I fragment_index
may also be the special value
.BR GD_ALL_FRAGMENTS ,
which indicates that the frame offset of all fragments in the database should
be changed.

If the
.I recode
argument is non-zero, this call will shift the binary data of affected
.B 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
.B RAW
fields is reset to the beginning-of-frame.

If
.I recode
is zero, affected binary files are left untouched.

.SH RETURN VALUE
Upon successful completion,
.BR 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:
.TP 8
.B GD_E_ACCMODE
The specified dirfile was opened read-only.
.TP
.B GD_E_ALLOC
The library was unable to allocate memory.
.TP
.B GD_E_BAD_DIRFILE
The supplied dirfile was invalid.
.TP
.B GD_E_BAD_INDEX
The supplied index was out of range.
.TP
.B GD_E_IO
An I/O error occurred while attempting to shift a binary file.
.TP
.B 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.
.TP
.B GD_E_RANGE
The supplied offset was less than zero.
.TP
.B 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
.B 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.
.TP
.B GD_E_UNKNOWN_ENCODING
The encoding scheme of the fragment is unknown.
.TP
.B GD_E_UNSUPPORTED
The encoding scheme of the fragment does not support binary file shifting.
.PP
The dirfile error may be retrieved by calling
.BR gd_error (3).
A descriptive error string for the last error encountered can be obtained from
a call to
.BR gd_error_string (3).
.SH 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
.B RAW
fields in the fragment both before and after translation.  If all fragments
are updated by specifying
.BR GD_ALL_FRAGMENTS ,
the shifting occurs one fragment at a time.

An error code of
.B 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
@absolute_docdir@/unclean_database_recovery.txt.
.SH SEE ALSO
.BR gd_open (3),
.BR gd_error (3),
.BR gd_error_string (3),
.BR gd_frameoffset (3),
.BR dirfile (5),
.BR dirfile-format (5)
