date and time created 91/07/26 15:42:59 by bostic

[unix-history] / usr / src / bin / dd / position.c

/*-
* Copyright (c) 1991 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Keith Muller of the University of California, San Diego.
*
* %sccs.include.redist.c%
*/

#ifndef lint
static char sccsid[] = "@(#)position.c  5.1 (Berkeley) %G%";
#endif /* not lint */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mtio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include "dd.h"
#include "extern.h"

/*
* Position input/output data streams before starting the copy.  Device type
* dependent.  Seekable devices use lseek, and the rest position by reading.
* Seeking past the end of file can cause null blocks to be written to the
* output.
*/
void
pos_in()
{
       register int bcnt, cnt, nr, warned;

       /* If not a character, pipe or tape device, try to seek on it. */
       if (!(in.flags & (ISCHR|ISPIPE|ISTAPE))) {
               if (lseek(in.fd, (off_t)(in.offset * in.dbsz), SEEK_CUR) == -1)
                       err("%s: %s", in.name, strerror(errno));
               return;
       }

       /*
        * Read the data.  If a pipe, read until satisfy the number of bytes
        * being skipped.  No differentiation for reading complete and partial
        * blocks for other devices.
        */
       for (bcnt = in.dbsz, cnt = in.offset, warned = 0; cnt;) {
               if ((nr = read(in.fd, in.db, bcnt)) > 0)
                       if (in.flags & ISPIPE) {
                               if (!(bcnt -= nr)) {
                                       bcnt = in.dbsz;
                                       --cnt;
                               }
                               continue;
                       } else
                               --cnt;

               if (nr == 0) {
                       if (files_cnt > 1) {
                               --files_cnt;
                               continue;
                       }
                       err("skip reached end of input");
               }

               /*
                * Input error -- either EOF with no more files, or I/O error.
                * If noerror not set die.  POSIX requires that the warning
                * message be followed by an I/O display.
                */
               if (ddflags & C_NOERROR) {
                       if (!warned) {
                               warn("%s: %s", in.name, strerror(errno));
                               warned = 1;
                               summary(0);
                       }
                       continue;
               }
               err("%s: %s", in.name, strerror(errno));
       }
}

void
pos_out()
{
       register int cnt, n;
       struct mtop t_op;

       /*
        * If not a tape, try seeking on the file.  Seeking on a pipe is
        * going to fail, but don't protect the user -- they shouldn't
        * have specified the seek operand.
        */
       if (!(out.flags & ISTAPE)) {
               if (lseek(out.fd,
                   (off_t)out.offset * out.dbsz, SEEK_SET) == -1)
                       err("%s: %s", out.name, strerror(errno));
               return;
       }

       /* If no read access, try using mtio. */
       if (out.flags & NOREAD) {
               t_op.mt_op = MTFSR;
               t_op.mt_count = out.offset;

               if (ioctl(out.fd, MTIOCTOP, &t_op) < 0)
                       err("%s: %s", out.name, strerror(errno));
               return;
       }

       /* Read it. */
       for (cnt = 0; cnt < out.offset; ++cnt) {
               if ((n = read(out.fd, out.db, out.dbsz)) > 0)
                       continue;

               if (n < 0)
                       err("%s: %s", out.name, strerror(errno));

               /*
                * If reach EOF, fill with NUL characters; first, back up over
                * the EOF mark.  Note, cnt has not yet been incremented, so
                * the EOF read does not count as a seek'd block.
                */
               t_op.mt_op = MTBSR;
               t_op.mt_count = 1;
               if (ioctl(out.fd, MTIOCTOP, &t_op) == -1)
                       err("%s: %s", out.name, strerror(errno));

               while (cnt++ < out.offset)
                       if ((n = write(out.fd, out.db, out.dbsz)) != out.dbsz)
                               err("%s: %s", out.name, strerror(errno));
               break;
       }
}