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 * %sccs.include.redist.c% 10 */ 11 12 #ifndef lint 13 static char sccsid[] = "@(#)position.c 8.3 (Berkeley) 04/02/94"; 14 #endif /* not lint */ 15 16 #include <sys/types.h> 17 #include <sys/stat.h> 18 #include <sys/ioctl.h> 19 #include <sys/mtio.h> 20 21 #include <err.h> 22 #include <errno.h> 23 #include <string.h> 24 #include <unistd.h> 25 26 #include "dd.h" 27 #include "extern.h" 28 29 /* 30 * Position input/output data streams before starting the copy. Device type 31 * dependent. Seekable devices use lseek, and the rest position by reading. 32 * Seeking past the end of file can cause null blocks to be written to the 33 * output. 34 */ 35 void 36 pos_in() 37 { 38 int bcnt, cnt, nr, warned; 39 40 /* If not a character, pipe or tape device, try to seek on it. */ 41 if (!(in.flags & (ISCHR|ISPIPE|ISTAPE))) { 42 if (lseek(in.fd, (off_t)(in.offset * in.dbsz), SEEK_CUR) == -1) 43 err(1, "%s", in.name); 44 return; 45 } 46 47 /* 48 * Read the data. If a pipe, read until satisfy the number of bytes 49 * being skipped. No differentiation for reading complete and partial 50 * blocks for other devices. 51 */ 52 for (bcnt = in.dbsz, cnt = in.offset, warned = 0; cnt;) { 53 if ((nr = read(in.fd, in.db, bcnt)) > 0) { 54 if (in.flags & ISPIPE) { 55 if (!(bcnt -= nr)) { 56 bcnt = in.dbsz; 57 --cnt; 58 } 59 } else 60 --cnt; 61 continue; 62 } 63 64 if (nr == 0) { 65 if (files_cnt > 1) { 66 --files_cnt; 67 continue; 68 } 69 errx(1, "skip reached end of input"); 70 } 71 72 /* 73 * Input error -- either EOF with no more files, or I/O error. 74 * If noerror not set die. POSIX requires that the warning 75 * message be followed by an I/O display. 76 */ 77 if (ddflags & C_NOERROR) { 78 if (!warned) { 79 warn("%s", in.name); 80 warned = 1; 81 summary(); 82 } 83 continue; 84 } 85 err(1, "%s", in.name); 86 } 87 } 88 89 void 90 pos_out() 91 { 92 struct mtop t_op; 93 int cnt, n; 94 95 /* 96 * If not a tape, try seeking on the file. Seeking on a pipe is 97 * going to fail, but don't protect the user -- they shouldn't 98 * have specified the seek operand. 99 */ 100 if (!(out.flags & ISTAPE)) { 101 if (lseek(out.fd, 102 (off_t)out.offset * out.dbsz, SEEK_SET) == -1) 103 err(1, "%s", out.name); 104 return; 105 } 106 107 /* If no read access, try using mtio. */ 108 if (out.flags & NOREAD) { 109 t_op.mt_op = MTFSR; 110 t_op.mt_count = out.offset; 111 112 if (ioctl(out.fd, MTIOCTOP, &t_op) < 0) 113 err(1, "%s", out.name); 114 return; 115 } 116 117 /* Read it. */ 118 for (cnt = 0; cnt < out.offset; ++cnt) { 119 if ((n = read(out.fd, out.db, out.dbsz)) > 0) 120 continue; 121 122 if (n < 0) 123 err(1, "%s", out.name); 124 125 /* 126 * If reach EOF, fill with NUL characters; first, back up over 127 * the EOF mark. Note, cnt has not yet been incremented, so 128 * the EOF read does not count as a seek'd block. 129 */ 130 t_op.mt_op = MTBSR; 131 t_op.mt_count = 1; 132 if (ioctl(out.fd, MTIOCTOP, &t_op) == -1) 133 err(1, "%s", out.name); 134 135 while (cnt++ < out.offset) 136 if ((n = write(out.fd, out.db, out.dbsz)) != out.dbsz) 137 err(1, "%s", out.name); 138 break; 139 } 140 } 141