unitbksp.c

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/*

  Copyright (C) 2000, 2001, Silicon Graphics, Inc.  All Rights Reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of version 2.1 of the GNU Lesser General Public License 
  as published by the Free Software Foundation.

  This program is distributed in the hope that it would be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  

  Further, this software is distributed without any warranty that it is
  free of the rightful claim of any third person regarding infringement 
  or the like.  Any license provided herein, whether implied or 
  otherwise, applies only to this software file.  Patent licenses, if
  any, provided herein do not apply to combinations of this program with 
  other software, or any other product whatsoever.  

  You should have received a copy of the GNU Lesser General Public 
  License along with this program; if not, write the Free Software 
  Foundation, Inc., 59 Temple Place - Suite 330, Boston MA 02111-1307, 
  USA.

  Contact information:  Silicon Graphics, Inc., 1600 Amphitheatre Pky,
  Mountain View, CA 94043, or:

  http://www.sgi.com

  For further information regarding this notice, see:

  http://oss.sgi.com/projects/GenInfo/NoticeExplan

*/



#pragma ident "@(#) libf/fio/unitbksp.c 92.1    06/18/99 18:38:26"

#include <errno.h>
#include <foreign.h>
#include <liberrno.h>
#include "fio.h"
#ifdef __mips
typedef long long _ftelltype;
#define LIBFSEEK fseek64
#define LIBFTELL ftell64
#define FTELLZERO 0LL
#else
typedef long _ftelltype;
#define LIBFSEEK fseek
#define LIBFTELL ftell
#define FTELLZERO 0L
#endif


/*
 *      _unit_bksp
 *
 *              Perform a backspace operation on a connected unit.
 *
 *      Return value:
 *
 *              0 on normal completion.  Error status if an error is 
 *              encountered.
 */

int
_unit_bksp(unit *cup)
{
        int             errn;
        unsigned char   tbuf[TBUFSZB], *tp;
        struct ffsw     fst;
        int first_read;

        if (cup->useq == 0)     /* If direct access file */
                return(FEBKSPIV);       /* BACKSPACE invalid on dir. acc.*/

/*
 *      Wait for completion of a preceding asynchronous BUFFER IN/OUT.
 */

        WAITIO(cup, return(cup->uffsw.sw_error));

        if (cup->uwrt) {
                if (cup->utrunc) {
                        /*
                         * Truncate file after last sequential write before
                         * this BACKSPACE.
                         */
                        errn    = _unit_trunc(cup);
                        if (errn != 0)
                                return(errn);
                }
                cup->uwrt       = 0;
        }

/*
 *      According to the file structure make the appropriate request to
 *      backspace one logical record. 
 */
        switch( cup->ufs ) {

        case  FS_FDC:
                if ((cup->uend != LOGICAL_ENDFILE) || (cup->uspcproc==1)) {

                        errn    = XRCALL(cup->ufp.fdc, backrtn) cup->ufp.fdc,
                                &fst);

                        if (errn < 0)
                                return(fst.sw_error);
                }
                break;
 

        case  FS_TEXT:
        case  STD:
                /*
                 * Can't backspace pipes. sockets, ttys.  
                 */
                if (!cup->useek)
                        return(FENOBKPI);       /* can't backspace pipe */
 
                if (!cup->ufmt)         /* if not formatted */
                        return(FENOBKSP); /* can't backspace unblocked files */

                if (cup->uend) goto ok;

                first_read = 1;

                for ( ; ; ) {
                        ssize_t i;
                        size_t  ret;
                        _ftelltype x, y;

                        y       = LIBFTELL(cup->ufp.std);       
                        x       = y;

                        if (x < TBUFSZB)
                                x       = 0;
                        else
                                x -= TBUFSZB;

                        (void) LIBFSEEK(cup->ufp.std, x, 0);

                        /*
                         * starting at the current character position
                         * minus 2 chars, search backwards for a newline 
                         * character.
                         */

                        ret     = fread(tbuf, 1,(size_t)(y - x), cup->ufp.std);

                        if (ret < (y-x) && ferror(cup->ufp.std))
                                return(FEBSPNRD);

                        /* only the first time fread, we need to skip the
                         * first 2 chars
                         */
                        if (first_read) i = ret - 2;
                        else i = ret;
                        first_read = 0;

                        tp      = tbuf;

                        for ( ; i >= 0; i--) {
                                if ( *(tp+i) != '\n') continue;
                                (void) LIBFSEEK(cup->ufp.std, (_ftelltype)i+1-ret, 1);
                                goto ok;
                        }

                        if (x == 0) {
                                (void) LIBFSEEK(cup->ufp.std, FTELLZERO, 0);
                                goto ok;
                        } 
                        else
                                if (ret <= 0)   /* Should never occur */
                                        return(FEINTUNK);

                        (void) LIBFSEEK(cup->ufp.std, x, 0);
                }
 
        case FS_BIN:
                return(FENOBKSP);


        case FS_AUX:
                errn    = FEMIXAUX;        /* BACKSPACE not allowed on a WAIO,
                                         * MSIO, DRIO, or AQIO file. */
                break;
        default:
                return(FEINTFST);
        }

ok:
        cup->uend       = BEFORE_ENDFILE;
        cup->ulastyp    = DT_NONE;
        cup->urecpos    = 0;

        return(0);
}