position.c revision 1557 
1/*-
2 * Copyright (c) 1991, 1993, 1994
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Keith Muller of the University of California, San Diego and Lance
7 * Visser of Convex Computer Corporation.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 *    notice, this list of conditions and the following disclaimer in the
16 *    documentation and/or other materials provided with the distribution.
17 * 3. All advertising materials mentioning features or use of this software
18 *    must display the following acknowledgement:
19 *	This product includes software developed by the University of
20 *	California, Berkeley and its contributors.
21 * 4. Neither the name of the University nor the names of its contributors
22 *    may be used to endorse or promote products derived from this software
23 *    without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 */
37
38#ifndef lint
39static char sccsid[] = "@(#)position.c	8.3 (Berkeley) 4/2/94";
40#endif /* not lint */
41
42#include <sys/types.h>
43#include <sys/stat.h>
44#include <sys/ioctl.h>
45#include <sys/mtio.h>
46
47#include <err.h>
48#include <errno.h>
49#include <string.h>
50#include <unistd.h>
51
52#include "dd.h"
53#include "extern.h"
54
55/*
56 * Position input/output data streams before starting the copy.  Device type
57 * dependent.  Seekable devices use lseek, and the rest position by reading.
58 * Seeking past the end of file can cause null blocks to be written to the
59 * output.
60 */
61void
62pos_in()
63{
64	int bcnt, cnt, nr, warned;
65
66	/* If not a character, pipe or tape device, try to seek on it. */
67	if (!(in.flags & (ISCHR|ISPIPE|ISTAPE))) {
68		if (lseek(in.fd, (off_t)(in.offset * in.dbsz), SEEK_CUR) == -1)
69			err(1, "%s", in.name);
70		return;
71	}
72
73	/*
74	 * Read the data.  If a pipe, read until satisfy the number of bytes
75	 * being skipped.  No differentiation for reading complete and partial
76	 * blocks for other devices.
77	 */
78	for (bcnt = in.dbsz, cnt = in.offset, warned = 0; cnt;) {
79		if ((nr = read(in.fd, in.db, bcnt)) > 0) {
80			if (in.flags & ISPIPE) {
81				if (!(bcnt -= nr)) {
82					bcnt = in.dbsz;
83					--cnt;
84				}
85			} else
86				--cnt;
87			continue;
88		}
89
90		if (nr == 0) {
91			if (files_cnt > 1) {
92				--files_cnt;
93				continue;
94			}
95			errx(1, "skip reached end of input");
96		}
97
98		/*
99		 * Input error -- either EOF with no more files, or I/O error.
100		 * If noerror not set die.  POSIX requires that the warning
101		 * message be followed by an I/O display.
102		 */
103		if (ddflags & C_NOERROR) {
104			if (!warned) {
105				warn("%s", in.name);
106				warned = 1;
107				summary();
108			}
109			continue;
110		}
111		err(1, "%s", in.name);
112	}
113}
114
115void
116pos_out()
117{
118	struct mtop t_op;
119	int cnt, n;
120
121	/*
122	 * If not a tape, try seeking on the file.  Seeking on a pipe is
123	 * going to fail, but don't protect the user -- they shouldn't
124	 * have specified the seek operand.
125	 */
126	if (!(out.flags & ISTAPE)) {
127		if (lseek(out.fd,
128		    (off_t)out.offset * out.dbsz, SEEK_SET) == -1)
129			err(1, "%s", out.name);
130		return;
131	}
132
133	/* If no read access, try using mtio. */
134	if (out.flags & NOREAD) {
135		t_op.mt_op = MTFSR;
136		t_op.mt_count = out.offset;
137
138		if (ioctl(out.fd, MTIOCTOP, &t_op) < 0)
139			err(1, "%s", out.name);
140		return;
141	}
142
143	/* Read it. */
144	for (cnt = 0; cnt < out.offset; ++cnt) {
145		if ((n = read(out.fd, out.db, out.dbsz)) > 0)
146			continue;
147
148		if (n < 0)
149			err(1, "%s", out.name);
150
151		/*
152		 * If reach EOF, fill with NUL characters; first, back up over
153		 * the EOF mark.  Note, cnt has not yet been incremented, so
154		 * the EOF read does not count as a seek'd block.
155		 */
156		t_op.mt_op = MTBSR;
157		t_op.mt_count = 1;
158		if (ioctl(out.fd, MTIOCTOP, &t_op) == -1)
159			err(1, "%s", out.name);
160
161		while (cnt++ < out.offset)
162			if ((n = write(out.fd, out.db, out.dbsz)) != out.dbsz)
163				err(1, "%s", out.name);
164		break;
165	}
166}
167