lib/libc/stdio/fseeko.c

   1 /*      $NetBSD: fseeko.c,v 1.12 2012/03/27 15:05:42 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 1.12 2012/03/27 15:05:42 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  */
  62 int
  63 fseeko(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                 whence = SEEK_SET;
 119                 havepos = 1;
 120                 break;
 121
 122         case SEEK_SET:
 123         case SEEK_END:
 124                 curoff = 0;             /* XXX just to keep gcc quiet */
 125                 havepos = 0;
 126                 break;
 127
 128         default:
 129                 errno = EINVAL;
 130                 FUNLOCKFILE(fp);
 131                 return -1;
 132         }
 133
 134         /*
 135          * Can only optimise if:
 136          *      reading (and not reading-and-writing);
 137          *      not unbuffered; and
 138          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 139          * We must check __NBF first, because it is possible to have __NBF
 140          * and __SOPT both set.
 141          */
 142         if (fp->_bf._base == NULL)
 143                 __smakebuf(fp);
 144         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 145                 goto dumb;
 146         if ((fp->_flags & __SOPT) == 0) {
 147                 if (seekfn != __sseek ||
 148                     __sfileno(fp) == -1 || fstat(__sfileno(fp), &st) ||
 149                     !S_ISREG(st.st_mode)) {
 150                         fp->_flags |= __SNPT;
 151                         goto dumb;
 152                 }
 153                 fp->_blksize = st.st_blksize;
 154                 fp->_flags |= __SOPT;
 155         }
 156
 157         /*
 158          * We are reading; we can try to optimise.
 159          * Figure out where we are going and where we are now.
 160          */
 161         if (whence == SEEK_SET)
 162                 target = offset;
 163         else {
 164                 if (fstat(__sfileno(fp), &st))
 165                         goto dumb;
 166                 target = st.st_size + offset;
 167         }
 168
 169         if (!havepos) {
 170                 if (fp->_flags & __SOFF)
 171                         curoff = fp->_offset;
 172                 else {
 173                         curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR);
 174                         if (curoff == POS_ERR)
 175                                 goto dumb;
 176                 }
 177                 curoff -= fp->_r;
 178                 if (HASUB(fp))
 179                         curoff -= fp->_ur;
 180         }
 181
 182         /*
 183          * Compute the number of bytes in the input buffer (pretending
 184          * that any ungetc() input has been discarded).  Adjust current
 185          * offset backwards by this count so that it represents the
 186          * file offset for the first byte in the current input buffer.
 187          */
 188         if (HASUB(fp)) {
 189                 curoff += fp->_r;       /* kill off ungetc */
 190                 n = fp->_up - fp->_bf._base;
 191                 curoff -= n;
 192                 n += fp->_ur;
 193         } else {
 194                 n = fp->_p - fp->_bf._base;
 195                 curoff -= n;
 196                 n += fp->_r;
 197         }
 198
 199         /*
 200          * If the target offset is within the current buffer,
 201          * simply adjust the pointers, clear EOF, undo ungetc(),
 202          * and return.  (If the buffer was modified, we have to
 203          * skip this; see fgetln.c.)
 204          */
 205         if ((fp->_flags & __SMOD) == 0 &&
 206             target >= curoff && target < curoff + (off_t)n) {
 207                 int o = (int)(target - curoff);
 208
 209                 fp->_p = fp->_bf._base + o;
 210                 _DIAGASSERT(__type_fit(int, n - o));
 211                 fp->_r = (int)(n - o);
 212                 if (HASUB(fp))
 213                         FREEUB(fp);
 214                 fp->_flags &= ~__SEOF;
 215                 FUNLOCKFILE(fp);
 216                 return 0;
 217         }
 218
 219         /*
 220          * The place we want to get to is not within the current buffer,
 221          * but we can still be kind to the kernel copyout mechanism.
 222          * By aligning the file offset to a block boundary, we can let
 223          * the kernel use the VM hardware to map pages instead of
 224          * copying bytes laboriously.  Using a block boundary also
 225          * ensures that we only read one block, rather than two.
 226          */
 227         curoff = target & ~(fp->_blksize - 1);
 228         if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 229                 goto dumb;
 230         fp->_r = 0;
 231         fp->_p = fp->_bf._base;
 232         if (HASUB(fp))
 233                 FREEUB(fp);
 234         fp->_flags &= ~__SEOF;
 235         n = (int)(target - curoff);
 236         if (n) {
 237                 if (__srefill(fp) || (size_t)fp->_r < n)
 238                         goto dumb;
 239                 fp->_p += n;
 240                 _DIAGASSERT(__type_fit(int, fp->_r - n));
 241                 fp->_r -= (int)n;
 242         }
 243         FUNLOCKFILE(fp);
 244         return 0;
 245
 246         /*
 247          * We get here if we cannot optimise the seek ... just
 248          * do it.  Allow the seek function to change fp->_bf._base.
 249          */
 250 dumb:
 251         if (__sflush(fp) ||
 252             (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) {
 253                 FUNLOCKFILE(fp);
 254                 return -1;
 255         }
 256         /* success: clear EOF indicator and discard ungetc() data */
 257         if (HASUB(fp))
 258                 FREEUB(fp);
 259         fp->_p = fp->_bf._base;
 260         fp->_r = 0;
 261         /* fp->_w = 0; */       /* unnecessary (I think...) */
 262         fp->_flags &= ~__SEOF;
 263         FUNLOCKFILE(fp);
 264         return 0;
 265 }