fseeko.c revision 1.14
1/* $NetBSD: fseeko.c,v 1.14 2017/01/10 17:44:28 christos Exp $ */ 2 3/*- 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Chris Torek. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35#include <sys/cdefs.h> 36#if defined(LIBC_SCCS) && !defined(lint) 37__RCSID("$NetBSD: fseeko.c,v 1.14 2017/01/10 17:44:28 christos Exp $"); 38#endif /* LIBC_SCCS and not lint */ 39 40#include "namespace.h" 41#include <sys/types.h> 42#include <sys/stat.h> 43 44#include <assert.h> 45#include <errno.h> 46#include <fcntl.h> 47#include <stdio.h> 48#include <stdlib.h> 49#include "reentrant.h" 50#include "local.h" 51 52#ifdef __weak_alias 53__weak_alias(fseeko, _fseeko) 54#endif 55 56#define POS_ERR ((off_t)-1) 57 58/* 59 * Seek the given file to the given offset. 60 * `Whence' must be one of the three SEEK_* macros. 61 */ 62int 63fseeko(FILE *fp, off_t offset, int whence) 64{ 65 off_t (*seekfn)(void *, off_t, int); 66 off_t target, curoff; 67 size_t n; 68 struct stat st; 69 int havepos; 70 71 _DIAGASSERT(fp != NULL); 72 73 /* make sure stdio is set up */ 74 if (!__sdidinit) 75 __sinit(); 76 77 FLOCKFILE(fp); 78 79 /* 80 * Have to be able to seek. 81 */ 82 if ((seekfn = fp->_seek) == NULL) { 83 errno = ESPIPE; /* historic practice */ 84 FUNLOCKFILE(fp); 85 return -1; 86 } 87 88 /* 89 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. 90 * After this, whence is either SEEK_SET or SEEK_END. 91 */ 92 switch (whence) { 93 94 case SEEK_CUR: 95 /* 96 * In order to seek relative to the current stream offset, 97 * we have to first find the current stream offset a la 98 * ftell (see ftell for details). 99 */ 100 (void)__sflush(fp); /* may adjust seek offset on append stream */ 101 if (fp->_flags & __SOFF) 102 curoff = fp->_offset; 103 else { 104 curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR); 105 if (curoff == POS_ERR) { 106 FUNLOCKFILE(fp); 107 return -1; 108 } 109 } 110 if (fp->_flags & __SRD) { 111 curoff -= fp->_r; 112 if (HASUB(fp)) 113 curoff -= fp->_ur; 114 } else if (fp->_flags & __SWR && fp->_p != NULL) 115 curoff += fp->_p - fp->_bf._base; 116 117 offset += curoff; 118 if (offset < 0) { 119 errno = EINVAL; 120 FUNLOCKFILE(fp); 121 return -1; 122 } 123 whence = SEEK_SET; 124 havepos = 1; 125 break; 126 127 case SEEK_SET: 128 if (offset < 0) { 129 errno = EINVAL; 130 FUNLOCKFILE(fp); 131 return -1; 132 } 133 /*FALLTHROUGH*/ 134 case SEEK_END: 135 curoff = 0; /* XXX just to keep gcc quiet */ 136 havepos = 0; 137 break; 138 139 default: 140 errno = EINVAL; 141 FUNLOCKFILE(fp); 142 return -1; 143 } 144 145 /* 146 * Can only optimise if: 147 * reading (and not reading-and-writing); 148 * not unbuffered; and 149 * this is a `regular' Unix file (and hence seekfn==__sseek). 150 * We must check __NBF first, because it is possible to have __NBF 151 * and __SOPT both set. 152 */ 153 if (fp->_bf._base == NULL) 154 __smakebuf(fp); 155 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) 156 goto dumb; 157 if ((fp->_flags & __SOPT) == 0) { 158 if (seekfn != __sseek || 159 __sfileno(fp) == -1 || fstat(__sfileno(fp), &st) || 160 !S_ISREG(st.st_mode)) { 161 fp->_flags |= __SNPT; 162 goto dumb; 163 } 164 fp->_blksize = st.st_blksize; 165 fp->_flags |= __SOPT; 166 } 167 168 /* 169 * We are reading; we can try to optimise. 170 * Figure out where we are going and where we are now. 171 */ 172 if (whence == SEEK_SET) 173 target = offset; 174 else { 175 if (fstat(__sfileno(fp), &st)) 176 goto dumb; 177 target = st.st_size + offset; 178 } 179 180 if (!havepos) { 181 if (fp->_flags & __SOFF) 182 curoff = fp->_offset; 183 else { 184 curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR); 185 if (curoff == POS_ERR) 186 goto dumb; 187 } 188 curoff -= fp->_r; 189 if (HASUB(fp)) 190 curoff -= fp->_ur; 191 } 192 193 /* 194 * Compute the number of bytes in the input buffer (pretending 195 * that any ungetc() input has been discarded). Adjust current 196 * offset backwards by this count so that it represents the 197 * file offset for the first byte in the current input buffer. 198 */ 199 if (HASUB(fp)) { 200 curoff += fp->_r; /* kill off ungetc */ 201 n = fp->_up - fp->_bf._base; 202 curoff -= n; 203 n += fp->_ur; 204 } else { 205 n = fp->_p - fp->_bf._base; 206 curoff -= n; 207 n += fp->_r; 208 } 209 210 /* 211 * If the target offset is within the current buffer, 212 * simply adjust the pointers, clear EOF, undo ungetc(), 213 * and return. (If the buffer was modified, we have to 214 * skip this; see fgetln.c.) 215 */ 216 if ((fp->_flags & __SMOD) == 0 && 217 target >= curoff && target < curoff + (off_t)n) { 218 int o = (int)(target - curoff); 219 220 fp->_p = fp->_bf._base + o; 221 _DIAGASSERT(__type_fit(int, n - o)); 222 fp->_r = (int)(n - o); 223 if (HASUB(fp)) 224 FREEUB(fp); 225 fp->_flags &= ~__SEOF; 226 FUNLOCKFILE(fp); 227 return 0; 228 } 229 230 /* 231 * The place we want to get to is not within the current buffer, 232 * but we can still be kind to the kernel copyout mechanism. 233 * By aligning the file offset to a block boundary, we can let 234 * the kernel use the VM hardware to map pages instead of 235 * copying bytes laboriously. Using a block boundary also 236 * ensures that we only read one block, rather than two. 237 */ 238 curoff = target & ~(fp->_blksize - 1); 239 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) 240 goto dumb; 241 fp->_r = 0; 242 fp->_p = fp->_bf._base; 243 if (HASUB(fp)) 244 FREEUB(fp); 245 fp->_flags &= ~__SEOF; 246 n = (int)(target - curoff); 247 if (n) { 248 if (__srefill(fp) || (size_t)fp->_r < n) 249 goto dumb; 250 fp->_p += n; 251 _DIAGASSERT(__type_fit(int, fp->_r - n)); 252 fp->_r -= (int)n; 253 } 254 FUNLOCKFILE(fp); 255 return 0; 256 257 /* 258 * We get here if we cannot optimise the seek ... just 259 * do it. Allow the seek function to change fp->_bf._base. 260 */ 261dumb: 262 if (__sflush(fp) || 263 (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) { 264 FUNLOCKFILE(fp); 265 return -1; 266 } 267 /* success: clear EOF indicator and discard ungetc() data */ 268 if (HASUB(fp)) 269 FREEUB(fp); 270 fp->_p = fp->_bf._base; 271 fp->_r = 0; 272 /* fp->_w = 0; */ /* unnecessary (I think...) */ 273 fp->_flags &= ~__SEOF; 274 FUNLOCKFILE(fp); 275 return 0; 276} 277