gold/ftruncate.c

   1 /* ftruncate emulations that work on some System V's.
   2    This file is in the public domain.  */
   3
   4 /* Copyright (C) 2012-2020 Free Software Foundation, Inc.
   5
   6    This file is part of gold.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21    MA 02110-1301, USA.  */
  22
  23 #include <config.h>
  24
  25 /* Specification.  */
  26 #include <unistd.h>
  27
  28 #include <sys/types.h>
  29 #include <fcntl.h>
  30
  31 extern int ftruncate (int, off_t);
  32
  33 #ifdef F_CHSIZE
  34
  35 int
  36 ftruncate (int fd, off_t length)
  37 {
  38   return fcntl (fd, F_CHSIZE, length);
  39 }
  40
  41 #else /* not F_CHSIZE */
  42 # ifdef F_FREESP
  43
  44 /* By William Kucharski <kucharsk@netcom.com>.  */
  45
  46 #  include <sys/stat.h>
  47 #  include <errno.h>
  48
  49 int
  50 ftruncate (int fd, off_t length)
  51 {
  52   struct flock fl;
  53   struct stat filebuf;
  54
  55   if (fstat (fd, &filebuf) < 0)
  56     return -1;
  57
  58   if (filebuf.st_size < length)
  59     {
  60       /* Extend file length. */
  61       if (lseek (fd, (length - 1), SEEK_SET) < 0)
  62         return -1;
  63
  64       /* Write a "0" byte. */
  65       if (write (fd, "", 1) != 1)
  66         return -1;
  67     }
  68   else
  69     {
  70
  71       /* Truncate length. */
  72
  73       fl.l_whence = 0;
  74       fl.l_len = 0;
  75       fl.l_start = length;
  76       fl.l_type = F_WRLCK;      /* write lock on file space */
  77
  78       /* This relies on the *undocumented* F_FREESP argument to fcntl,
  79          which truncates the file so that it ends at the position
  80          indicated by fl.l_start.  Will minor miracles never cease?  */
  81
  82       if (fcntl (fd, F_FREESP, &fl) < 0)
  83         return -1;
  84     }
  85
  86   return 0;
  87 }
  88
  89 # else /* not F_CHSIZE nor F_FREESP */
  90 #  if HAVE_CHSIZE                      /* native Windows, e.g. mingw */
  91
  92 int
  93 ftruncate (int fd, off_t length)
  94 {
  95   return chsize (fd, length);
  96 }
  97
  98 #  else /* not F_CHSIZE nor F_FREESP nor HAVE_CHSIZE */
  99
 100 #   include <errno.h>
 101
 102 int
 103 ftruncate (int fd, off_t length)
 104 {
 105   errno = EIO;
 106   return -1;
 107 }
 108
 109 #  endif /* not HAVE_CHSIZE */
 110 # endif /* not F_FREESP */
 111 #endif /* not F_CHSIZE */