position.c revision 321140
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 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#ifndef lint
35#if 0
36static char sccsid[] = "@(#)position.c	8.3 (Berkeley) 4/2/94";
37#endif
38#endif /* not lint */
39#include <sys/cdefs.h>
40__FBSDID("$FreeBSD: stable/10/bin/dd/position.c 321140 2017-07-18 17:36:25Z ngie $");
41
42#include <sys/types.h>
43#include <sys/mtio.h>
44
45#include <err.h>
46#include <errno.h>
47#include <inttypes.h>
48#include <limits.h>
49#include <signal.h>
50#include <unistd.h>
51
52#include "dd.h"
53#include "extern.h"
54
55static off_t
56seek_offset(IO *io)
57{
58	off_t n;
59	size_t sz;
60
61	n = io->offset;
62	sz = io->dbsz;
63
64	_Static_assert(sizeof(io->offset) == sizeof(int64_t), "64-bit off_t");
65
66	/*
67	 * If the lseek offset will be negative, verify that this is a special
68	 * device file.  Some such files (e.g. /dev/kmem) permit "negative"
69	 * offsets.
70	 *
71	 * Bail out if the calculation of a file offset would overflow.
72	 */
73	if ((io->flags & ISCHR) == 0 && (n < 0 || n > OFF_MAX / (ssize_t)sz))
74		errx(1, "seek offsets cannot be larger than %jd",
75		    (intmax_t)OFF_MAX);
76	else if ((io->flags & ISCHR) != 0 && (uint64_t)n > UINT64_MAX / sz)
77		errx(1, "seek offsets cannot be larger than %ju",
78		    (uintmax_t)UINT64_MAX);
79
80	return ((off_t)( (uint64_t)n * sz ));
81}
82
83/*
84 * Position input/output data streams before starting the copy.  Device type
85 * dependent.  Seekable devices use lseek, and the rest position by reading.
86 * Seeking past the end of file can cause null blocks to be written to the
87 * output.
88 */
89void
90pos_in(void)
91{
92	off_t cnt;
93	int warned;
94	ssize_t nr;
95	size_t bcnt;
96
97	/* If known to be seekable, try to seek on it. */
98	if (in.flags & ISSEEK) {
99		errno = 0;
100		if (lseek(in.fd, seek_offset(&in), SEEK_CUR) == -1 &&
101		    errno != 0)
102			err(1, "%s", in.name);
103		return;
104	}
105
106	/* Don't try to read a really weird amount (like negative). */
107	if (in.offset < 0)
108		errx(1, "%s: illegal offset", "iseek/skip");
109
110	/*
111	 * Read the data.  If a pipe, read until satisfy the number of bytes
112	 * being skipped.  No differentiation for reading complete and partial
113	 * blocks for other devices.
114	 */
115	for (bcnt = in.dbsz, cnt = in.offset, warned = 0; cnt;) {
116		if ((nr = read(in.fd, in.db, bcnt)) > 0) {
117			if (in.flags & ISPIPE) {
118				if (!(bcnt -= nr)) {
119					bcnt = in.dbsz;
120					--cnt;
121				}
122			} else
123				--cnt;
124			if (need_summary)
125				summary();
126			continue;
127		}
128
129		if (nr == 0) {
130			if (files_cnt > 1) {
131				--files_cnt;
132				continue;
133			}
134			errx(1, "skip reached end of input");
135		}
136
137		/*
138		 * Input error -- either EOF with no more files, or I/O error.
139		 * If noerror not set die.  POSIX requires that the warning
140		 * message be followed by an I/O display.
141		 */
142		if (ddflags & C_NOERROR) {
143			if (!warned) {
144				warn("%s", in.name);
145				warned = 1;
146				summary();
147			}
148			continue;
149		}
150		err(1, "%s", in.name);
151	}
152}
153
154void
155pos_out(void)
156{
157	struct mtop t_op;
158	off_t cnt;
159	ssize_t n;
160
161	/*
162	 * If not a tape, try seeking on the file.  Seeking on a pipe is
163	 * going to fail, but don't protect the user -- they shouldn't
164	 * have specified the seek operand.
165	 */
166	if (out.flags & (ISSEEK | ISPIPE)) {
167		errno = 0;
168		if (lseek(out.fd, seek_offset(&out), SEEK_CUR) == -1 &&
169		    errno != 0)
170			err(1, "%s", out.name);
171		return;
172	}
173
174	/* Don't try to read a really weird amount (like negative). */
175	if (out.offset < 0)
176		errx(1, "%s: illegal offset", "oseek/seek");
177
178	/* If no read access, try using mtio. */
179	if (out.flags & NOREAD) {
180		t_op.mt_op = MTFSR;
181		t_op.mt_count = out.offset;
182
183		if (ioctl(out.fd, MTIOCTOP, &t_op) == -1)
184			err(1, "%s", out.name);
185		return;
186	}
187
188	/* Read it. */
189	for (cnt = 0; cnt < out.offset; ++cnt) {
190		if ((n = read(out.fd, out.db, out.dbsz)) > 0)
191			continue;
192
193		if (n == -1)
194			err(1, "%s", out.name);
195
196		/*
197		 * If reach EOF, fill with NUL characters; first, back up over
198		 * the EOF mark.  Note, cnt has not yet been incremented, so
199		 * the EOF read does not count as a seek'd block.
200		 */
201		t_op.mt_op = MTBSR;
202		t_op.mt_count = 1;
203		if (ioctl(out.fd, MTIOCTOP, &t_op) == -1)
204			err(1, "%s", out.name);
205
206		while (cnt++ < out.offset) {
207			n = write(out.fd, out.db, out.dbsz);
208			if (n == -1)
209				err(1, "%s", out.name);
210			if ((size_t)n != out.dbsz)
211				errx(1, "%s: write failure", out.name);
212		}
213		break;
214	}
215}
216