src/system/libroot/posix/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
  37 #include <ktypes.h>
  38 #include <sys/stat.h>
  39 #include <fcntl.h>
  40 #include <stdio.h>
  41 #include <stdlib.h>
  42 #include <errno.h>
  43
  44 #include <errno_private.h>
  45
  46 #include "local.h"
  47
  48 #define POS_ERR (-(fpos_t)1)
  49
  50 /*
  51  * Seek the given file to the given offset.
  52  * `Whence' must be one of the three SEEK_* macros.
  53  */
  54 int
  55 fseeko(fp, offset, whence)
  56         register FILE *fp;
  57         off_t offset;
  58         int whence;
  59 {
  60         register fpos_t (*seekfn) (void *, fpos_t, int);
  61         fpos_t target, curoff;
  62         size_t n;
  63         struct stat st;
  64         int havepos;
  65
  66         /* make sure stdio is set up */
  67         if (!__sdidinit)
  68                 __sinit();
  69
  70         /*
  71          * Have to be able to seek.
  72          */
  73         if ((seekfn = fp->_seek) == NULL) {
  74                 __set_errno(ESPIPE);                    /* historic practice */
  75                 return (EOF);
  76         }
  77
  78         /*
  79          * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
  80          * After this, whence is either SEEK_SET or SEEK_END.
  81          */
  82         switch (whence) {
  83
  84         case SEEK_CUR:
  85                 /*
  86                  * In order to seek relative to the current stream offset,
  87                  * we have to first find the current stream offset a la
  88                  * ftell (see ftell for details).
  89                  */
  90                 __sflush(fp);   /* may adjust seek offset on append stream */
  91                 if (fp->_flags & __SOFF)
  92                         curoff = fp->_offset;
  93                 else {
  94                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
  95                         if (curoff == (fpos_t)-1)
  96                                 return (EOF);
  97                 }
  98                 if (fp->_flags & __SRD) {
  99                         curoff -= fp->_r;
 100                         if (HASUB(fp))
 101                                 curoff -= fp->_ur;
 102                 } else if (fp->_flags & __SWR && fp->_p != NULL)
 103                         curoff += fp->_p - fp->_bf._base;
 104
 105                 offset += curoff;
 106                 whence = SEEK_SET;
 107                 havepos = 1;
 108                 break;
 109
 110         case SEEK_SET:
 111         case SEEK_END:
 112                 curoff = 0;             /* XXX just to keep gcc quiet */
 113                 havepos = 0;
 114                 break;
 115
 116         default:
 117                 __set_errno(EINVAL);
 118                 return (EOF);
 119         }
 120
 121         /*
 122          * Can only optimise if:
 123          *      reading (and not reading-and-writing);
 124          *      not unbuffered; and
 125          *      this is a `regular' Unix file (and hence seekfn==__sseek).
 126          * We must check __NBF first, because it is possible to have __NBF
 127          * and __SOPT both set.
 128          */
 129         if (fp->_bf._base == NULL)
 130                 __smakebuf(fp);
 131         if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 132                 goto dumb;
 133         if ((fp->_flags & __SOPT) == 0) {
 134                 if (seekfn != __sseek ||
 135                     fp->_file < 0 || fstat(fp->_file, &st) ||
 136                     S_ISREG(st.st_mode)) {
 137                         fp->_flags |= __SNPT;
 138                         goto dumb;
 139                 }
 140                 fp->_blksize = st.st_blksize;
 141                 fp->_flags |= __SOPT;
 142         }
 143
 144         /*
 145          * We are reading; we can try to optimise.
 146          * Figure out where we are going and where we are now.
 147          */
 148         if (whence == SEEK_SET)
 149                 target = offset;
 150         else {
 151                 if (fstat(fp->_file, &st))
 152                         goto dumb;
 153                 target = st.st_size + offset;
 154         }
 155
 156         if (!havepos) {
 157                 if (fp->_flags & __SOFF)
 158                         curoff = fp->_offset;
 159                 else {
 160                         curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
 161                         if (curoff == POS_ERR)
 162                                 goto dumb;
 163                 }
 164                 curoff -= fp->_r;
 165                 if (HASUB(fp))
 166                         curoff -= fp->_ur;
 167         }
 168
 169         /*
 170          * Compute the number of bytes in the input buffer (pretending
 171          * that any ungetc() input has been discarded).  Adjust current
 172          * offset backwards by this count so that it represents the
 173          * file offset for the first byte in the current input buffer.
 174          */
 175         if (HASUB(fp)) {
 176                 curoff += fp->_r;       /* kill off ungetc */
 177                 n = fp->_up - fp->_bf._base;
 178                 curoff -= n;
 179                 n += fp->_ur;
 180         } else {
 181                 n = fp->_p - fp->_bf._base;
 182                 curoff -= n;
 183                 n += fp->_r;
 184         }
 185
 186         /*
 187          * If the target offset is within the current buffer,
 188          * simply adjust the pointers, clear EOF, undo ungetc(),
 189          * and return.  (If the buffer was modified, we have to
 190          * skip this; see fgetln.c.)
 191          */
 192         if ((fp->_flags & __SMOD) == 0 &&
 193             target >= curoff && target < curoff + n) {
 194                 register int o = target - curoff;
 195
 196                 fp->_p = fp->_bf._base + o;
 197                 fp->_r = n - o;
 198                 if (HASUB(fp))
 199                         FREEUB(fp);
 200                 fp->_flags &= ~__SEOF;
 201                 return (0);
 202         }
 203
 204         /*
 205          * The place we want to get to is not within the current buffer,
 206          * but we can still be kind to the kernel copyout mechanism.
 207          * By aligning the file offset to a block boundary, we can let
 208          * the kernel use the VM hardware to map pages instead of
 209          * copying bytes laboriously.  Using a block boundary also
 210          * ensures that we only read one block, rather than two.
 211          */
 212         curoff = target & ~(fp->_blksize - 1);
 213         if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
 214                 goto dumb;
 215         fp->_r = 0;
 216         fp->_p = fp->_bf._base;
 217         if (HASUB(fp))
 218                 FREEUB(fp);
 219         fp->_flags &= ~__SEOF;
 220         n = target - curoff;
 221         if (n) {
 222                 if (__srefill(fp) || fp->_r < n)
 223                         goto dumb;
 224                 fp->_p += n;
 225                 fp->_r -= n;
 226         }
 227         return (0);
 228
 229         /*
 230          * We get here if we cannot optimise the seek ... just
 231          * do it.  Allow the seek function to change fp->_bf._base.
 232          */
 233 dumb:
 234         if (__sflush(fp) ||
 235             (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 236                 return (EOF);
 237         }
 238         /* success: clear EOF indicator and discard ungetc() data */
 239         if (HASUB(fp))
 240                 FREEUB(fp);
 241         fp->_p = fp->_bf._base;
 242         fp->_r = 0;
 243         /* fp->_w = 0; */       /* unnecessary (I think...) */
 244         fp->_flags &= ~__SEOF;
 245         return (0);
 246 }
 247
 248 /*
 249  * fseek()'s offset is a long and sizeof(off_t) != sizeof(long) on all arches
 250  */
 251 #if defined(__alpha__) && defined(__indr_reference)
 252 __indr_reference(fseeko, fseek);
 253 #else
 254 int
 255 fseek(fp, offset, whence)
 256         register FILE *fp;
 257         long offset;
 258         int whence;
 259 {
 260         off_t off = offset;
 261
 262         return(fseeko(fp, off, whence));
 263 }
 264 #endif