lib/libc/stdio/fseek.c

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Chris Torek.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * @(#)fseek.c  8.3 (Berkeley) 1/2/94
  37  * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.9.2.1 2001/03/05 10:56:58 obrien Exp $
  38  * $DragonFly: src/lib/libc/stdio/fseek.c,v 1.10 2005/11/20 11:07:30 swildner Exp $
  39  */
  40
  41 #include "namespace.h"
  42 #include <sys/types.h>
  43 #include <sys/stat.h>
  44 #include <fcntl.h>
  45 #include <stdio.h>
  46 #include <stdlib.h>
  47 #include <errno.h>
  48 #include "un-namespace.h"
  49
  50 #include "local.h"
  51 #include "libc_private.h"
  52 #include "priv_stdio.h"
  53
  54 #define POS_ERR (-(fpos_t)1)
  55
  56 int
  57 fseek(FILE *fp, long offset, int whence)
  58 {
  59         return (fseeko(fp, offset, whence));
  60 }
  61
  62 int
  63 fseeko(FILE *fp, off_t offset, int whence)
  64 {
  65         int ret;
  66
  67         /* make sure stdio is set up */
  68         if (!__sdidinit)
  69                 __sinit();
  70
  71         FLOCKFILE(fp);
  72         ret = _fseeko(fp, offset, whence);
  73         FUNLOCKFILE(fp);
  74         return (ret);
  75 }
  76
  77 /*
  78  * Seek the given file to the given offset.
  79  * `Whence' must be one of the three SEEK_* macros.
  80  */
  81 int
  82 _fseeko(FILE *fp, off_t offset, int whence)
  83 {
  84         fpos_t (*seekfn) (void *, fpos_t, int);
  85         fpos_t target, curoff;
  86         size_t n;
  87         struct stat st;
  88         int havepos;
  89
  90         /*
  91          * Have to be able to seek.
  92          */
  93         if ((seekfn = fp->_seek) == NULL) {
  94                 errno = ESPIPE;         /* historic practice */
  95                 return (EOF);
  96         }
  97
  98         /*
  99          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 100          * After this, whence is either SEEK_SET or SEEK_END.
 101          */
 102         switch (whence) {
 103
 104         case SEEK_CUR:
 105                 /*
 106                  * In order to seek relative to the current stream offset,
 107                  * we have to first find the current stream offset a la
 108                  * ftell (see ftell for details).
 109                  */
 110                 if (fp->pub._flags & __SOFF)
 111                         curoff = fp->_offset;
 112                 else {
 113                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 114                         if (curoff == -1) {
 115                                 return (EOF);
 116                         }
 117                 }
 118                 if (fp->pub._flags & __SRD) {
 119                         curoff -= fp->pub._r;
 120                         if (HASUB(fp))
 121                                 curoff -= fp->_ur;
 122                 } else if (fp->pub._flags & __SWR && fp->pub._p != NULL)
 123                         curoff += fp->pub._p - fp->_bf._base;
 124
 125                 offset += curoff;
 126                 whence = SEEK_SET;
 127                 havepos = 1;
 128                 break;
 129
 130         case SEEK_SET:
 131         case SEEK_END:
 132                 curoff = 0;             /* XXX just to keep gcc quiet */
 133                 havepos = 0;
 134                 break;
 135
 136         default:
 137                 errno = EINVAL;
 138                 return (EOF);
 139         }
 140
 141         /*
 142          * Can only optimise if:
 143          *      reading (and not reading-and-writing);
 144          *      not unbuffered; and
 145          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 146          * We must check __NBF first, because it is possible to have __NBF
 147          * and __SOPT both set.
 148          */
 149         if (fp->_bf._base == NULL)
 150                 __smakebuf(fp);
 151         if (fp->pub._flags & (__SWR | __SRW | __SNBF | __SNPT))
 152                 goto dumb;
 153         if ((fp->pub._flags & __SOPT) == 0) {
 154                 if (seekfn != __sseek ||
 155                     fp->pub._fileno < 0 || _fstat(fp->pub._fileno, &st) ||
 156                     (st.st_mode & S_IFMT) != S_IFREG) {
 157                         fp->pub._flags |= __SNPT;
 158                         goto dumb;
 159                 }
 160                 fp->_blksize = st.st_blksize;
 161                 fp->pub._flags |= __SOPT;
 162         }
 163
 164         /*
 165          * We are reading; we can try to optimise.
 166          * Figure out where we are going and where we are now.
 167          */
 168         if (whence == SEEK_SET)
 169                 target = offset;
 170         else {
 171                 if (_fstat(fp->pub._fileno, &st))
 172                         goto dumb;
 173                 target = st.st_size + offset;
 174         }
 175
 176         if (!havepos) {
 177                 if (fp->pub._flags & __SOFF)
 178                         curoff = fp->_offset;
 179                 else {
 180                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 181                         if (curoff == POS_ERR)
 182                                 goto dumb;
 183                 }
 184                 curoff -= fp->pub._r;
 185                 if (HASUB(fp))
 186                         curoff -= fp->_ur;
 187         }
 188
 189         /*
 190          * Compute the number of bytes in the input buffer (pretending
 191          * that any ungetc() input has been discarded).  Adjust current
 192          * offset backwards by this count so that it represents the
 193          * file offset for the first byte in the current input buffer.
 194          */
 195         if (HASUB(fp)) {
 196                 curoff += fp->pub._r;   /* kill off ungetc */
 197                 n = fp->_up - fp->_bf._base;
 198                 curoff -= n;
 199                 n += fp->_ur;
 200         } else {
 201                 n = fp->pub._p - fp->_bf._base;
 202                 curoff -= n;
 203                 n += fp->pub._r;
 204         }
 205
 206         /*
 207          * If the target offset is within the current buffer,
 208          * simply adjust the pointers, clear EOF, undo ungetc(),
 209          * and return.  (If the buffer was modified, we have to
 210          * skip this; see fgetln.c.)
 211          */
 212         if ((fp->pub._flags & __SMOD) == 0 &&
 213             target >= curoff && target < curoff + n) {
 214                 int o = target - curoff;
 215
 216                 fp->pub._p = fp->_bf._base + o;
 217                 fp->pub._r = n - o;
 218                 if (HASUB(fp))
 219                         FREEUB(fp);
 220                 fp->pub._flags &= ~__SEOF;
 221                 return (0);
 222         }
 223
 224         /*
 225          * The place we want to get to is not within the current buffer,
 226          * but we can still be kind to the kernel copyout mechanism.
 227          * By aligning the file offset to a block boundary, we can let
 228          * the kernel use the VM hardware to map pages instead of
 229          * copying bytes laboriously.  Using a block boundary also
 230          * ensures that we only read one block, rather than two.
 231          */
 232         curoff = target & ~(fp->_blksize - 1);
 233         if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 234                 goto dumb;
 235         fp->pub._r = 0;
 236         fp->pub._p = fp->_bf._base;
 237         if (HASUB(fp))
 238                 FREEUB(fp);
 239         fp->pub._flags &= ~__SEOF;
 240         n = target - curoff;
 241         if (n) {
 242                 if (__srefill(fp) || fp->pub._r < n)
 243                         goto dumb;
 244                 fp->pub._p += n;
 245                 fp->pub._r -= n;
 246         }
 247         return (0);
 248
 249         /*
 250          * We get here if we cannot optimise the seek ... just
 251          * do it.  Allow the seek function to change fp->_bf._base.
 252          */
 253 dumb:
 254         if (__sflush(fp) ||
 255             (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 256                 return (EOF);
 257         }
 258         /* success: clear EOF indicator and discard ungetc() data */
 259         if (HASUB(fp))
 260                 FREEUB(fp);
 261         fp->pub._p = fp->_bf._base;
 262         fp->pub._r = 0;
 263         /* fp->pub._w = 0; */   /* unnecessary (I think...) */
 264         fp->pub._flags &= ~__SEOF;
 265         return (0);
 266 }