stdio.subproj/fseek.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1990, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * This code is derived from software contributed to Berkeley by
  27  * Chris Torek.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58
  59 #include <sys/types.h>
  60 #include <sys/types.h>
  61 #include <sys/stat.h>
  62 #include <fcntl.h>
  63 #include <stdio.h>
  64 #include <stdlib.h>
  65 #include <errno.h>
  66 #include "local.h"
  67
  68 #define POS_ERR (-(fpos_t)1)
  69
  70 int
  71 fseek(fp, offset, whence)
  72         register FILE *fp;
  73         long offset;
  74         int whence;
  75 {
  76         return (fseeko(fp, offset, whence));
  77 }
  78
  79
  80 /*
  81  * Seek the given file to the given offset.
  82  * `Whence' must be one of the three SEEK_* macros.
  83  */
  84 int
  85 fseeko(fp, offset, whence)
  86         register FILE *fp;
  87         off_t offset;
  88         int whence;
  89 {
  90         register fpos_t (*seekfn) __P((void *, fpos_t, int));
  91         fpos_t target, curoff;
  92         size_t n;
  93         struct stat st;
  94         int havepos;
  95
  96         /* make sure stdio is set up */
  97         if (!__sdidinit)
  98                 __sinit();
  99
 100         /* FLOCKFILE(fp); */
 101         /*
 102          * Have to be able to seek.
 103          */
 104         if ((seekfn = fp->_seek) == NULL) {
 105                 errno = ESPIPE;                 /* historic practice */
 106                 /* FUNLOCKFILE(fp); */
 107                 return (EOF);
 108         }
 109
 110         /*
 111          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
 112          * After this, whence is either SEEK_SET or SEEK_END.
 113          */
 114         switch (whence) {
 115
 116         case SEEK_CUR:
 117                 /*
 118                  * In order to seek relative to the current stream offset,
 119                  * we have to first find the current stream offset a la
 120                  * ftell (see ftell for details).
 121                  */
 122                 if (fp->_flags & __SOFF)
 123                         curoff = fp->_offset;
 124                 else {
 125                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 126                         if (curoff == -1) {
 127                                 /* FUNLOCKFILE(fp); */
 128                                 return (EOF);
 129                         }
 130                 }
 131                 if (fp->_flags & __SRD) {
 132                         curoff -= fp->_r;
 133                         if (HASUB(fp))
 134                                 curoff -= fp->_ur;
 135                 } else if (fp->_flags & __SWR && fp->_p != NULL)
 136                         curoff += fp->_p - fp->_bf._base;
 137
 138                 offset += curoff;
 139                 whence = SEEK_SET;
 140                 havepos = 1;
 141                 break;
 142
 143         case SEEK_SET:
 144         case SEEK_END:
 145                 curoff = 0;             /* XXX just to keep gcc quiet */
 146                 havepos = 0;
 147                 break;
 148
 149         default:
 150                 errno = EINVAL;
 151                 /* FUNLOCKFILE(fp); */
 152                 return (EOF);
 153         }
 154
 155         /*
 156          * Can only optimise if:
 157          *      reading (and not reading-and-writing);
 158          *      not unbuffered; and
 159          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 160          * We must check __NBF first, because it is possible to have __NBF
 161          * and __SOPT both set.
 162          */
 163         if (fp->_bf._base == NULL)
 164                 __smakebuf(fp);
 165         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 166                 goto dumb;
 167         if ((fp->_flags & __SOPT) == 0) {
 168                 if (seekfn != __sseek ||
 169                     fp->_file < 0 || fstat(fp->_file, &st) ||
 170                     (st.st_mode & S_IFMT) != S_IFREG) {
 171                         fp->_flags |= __SNPT;
 172                         goto dumb;
 173                 }
 174                 fp->_blksize = st.st_blksize;
 175                 fp->_flags |= __SOPT;
 176         }
 177
 178         /*
 179          * We are reading; we can try to optimise.
 180          * Figure out where we are going and where we are now.
 181          */
 182         if (whence == SEEK_SET)
 183                 target = offset;
 184         else {
 185                 if (fstat(fp->_file, &st))
 186                         goto dumb;
 187                 target = st.st_size + offset;
 188         }
 189
 190         if (!havepos) {
 191                 if (fp->_flags & __SOFF)
 192                         curoff = fp->_offset;
 193                 else {
 194                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 195                         if (curoff == POS_ERR)
 196                                 goto dumb;
 197                 }
 198                 curoff -= fp->_r;
 199                 if (HASUB(fp))
 200                         curoff -= fp->_ur;
 201         }
 202
 203         /*
 204          * Compute the number of bytes in the input buffer (pretending
 205          * that any ungetc() input has been discarded).  Adjust current
 206          * offset backwards by this count so that it represents the
 207          * file offset for the first byte in the current input buffer.
 208          */
 209         if (HASUB(fp)) {
 210                 curoff += fp->_r;       /* kill off ungetc */
 211                 n = fp->_up - fp->_bf._base;
 212                 curoff -= n;
 213                 n += fp->_ur;
 214         } else {
 215                 n = fp->_p - fp->_bf._base;
 216                 curoff -= n;
 217                 n += fp->_r;
 218         }
 219
 220         /*
 221          * If the target offset is within the current buffer,
 222          * simply adjust the pointers, clear EOF, undo ungetc(),
 223          * and return.  (If the buffer was modified, we have to
 224          * skip this; see fgetln.c.)
 225          */
 226         if ((fp->_flags & __SMOD) == 0 &&
 227             target >= curoff && target < curoff + n) {
 228                 register int o = target - curoff;
 229
 230                 fp->_p = fp->_bf._base + o;
 231                 fp->_r = n - o;
 232                 if (HASUB(fp))
 233                         FREEUB(fp);
 234                 fp->_flags &= ~__SEOF;
 235                 /* FUNLOCKFILE(fp); */
 236                 return (0);
 237         }
 238
 239         /*
 240          * The place we want to get to is not within the current buffer,
 241          * but we can still be kind to the kernel copyout mechanism.
 242          * By aligning the file offset to a block boundary, we can let
 243          * the kernel use the VM hardware to map pages instead of
 244          * copying bytes laboriously.  Using a block boundary also
 245          * ensures that we only read one block, rather than two.
 246          */
 247         curoff = target & ~(fp->_blksize - 1);
 248         if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 249                 goto dumb;
 250         fp->_r = 0;
 251         fp->_p = fp->_bf._base;
 252         if (HASUB(fp))
 253                 FREEUB(fp);
 254         fp->_flags &= ~__SEOF;
 255         n = target - curoff;
 256         if (n) {
 257                 if (__srefill(fp) || fp->_r < n)
 258                         goto dumb;
 259                 fp->_p += n;
 260                 fp->_r -= n;
 261         }
 262         /* FUNLOCKFILE(fp); */
 263         return (0);
 264
 265         /*
 266          * We get here if we cannot optimise the seek ... just
 267          * do it.  Allow the seek function to change fp->_bf._base.
 268          */
 269 dumb:
 270         if (__sflush(fp) ||
 271             (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 272                 /* FUNLOCKFILE(fp); */
 273                 return (EOF);
 274         }
 275         /* success: clear EOF indicator and discard ungetc() data */
 276         if (HASUB(fp))
 277                 FREEUB(fp);
 278         fp->_p = fp->_bf._base;
 279         fp->_r = 0;
 280         /* fp->_w = 0; */       /* unnecessary (I think...) */
 281         fp->_flags &= ~__SEOF;
 282         /* FUNLOCKFILE(fp); */
 283         return (0);
 284 }