lib/ftruncate.c

   1 /* ftruncate emulations that work on some System V's.
   2    This file is in the public domain.  */
   3
   4 #ifdef HAVE_CONFIG_H
   5 #include <config.h>
   6 #endif
   7
   8 #include <sys/types.h>
   9 #include <fcntl.h>
  10
  11 #ifdef F_CHSIZE
  12
  13 int
  14 ftruncate (fd, length)
  15      int fd;
  16      off_t length;
  17 {
  18   return fcntl (fd, F_CHSIZE, length);
  19 }
  20
  21 #else /* not F_CHSIZE */
  22 #ifdef F_FREESP
  23
  24 /* By William Kucharski <kucharsk@netcom.com>.  */
  25
  26 #include <sys/stat.h>
  27 #include <errno.h>
  28 #ifdef HAVE_UNISTD_H
  29 #include <unistd.h>
  30 #endif
  31
  32 int
  33 ftruncate (fd, length)
  34      int fd;
  35      off_t length;
  36 {
  37   struct flock fl;
  38   struct stat filebuf;
  39
  40   if (fstat (fd, &filebuf) < 0)
  41     return -1;
  42
  43   if (filebuf.st_size < length)
  44     {
  45       /* Extend file length. */
  46       if (lseek (fd, (length - 1), SEEK_SET) < 0)
  47         return -1;
  48
  49       /* Write a "0" byte. */
  50       if (write (fd, "", 1) != 1)
  51         return -1;
  52     }
  53   else
  54     {
  55
  56       /* Truncate length. */
  57
  58       fl.l_whence = 0;
  59       fl.l_len = 0;
  60       fl.l_start = length;
  61       fl.l_type = F_WRLCK;      /* write lock on file space */
  62
  63       /* This relies on the *undocumented* F_FREESP argument to fcntl,
  64          which truncates the file so that it ends at the position
  65          indicated by fl.l_start.  Will minor miracles never cease?  */
  66
  67       if (fcntl (fd, F_FREESP, &fl) < 0)
  68         return -1;
  69     }
  70
  71   return 0;
  72 }
  73
  74 #else /* not F_CHSIZE nor F_FREESP */
  75 #ifdef HAVE_CHSIZE
  76
  77 int
  78 ftruncate (fd, length)
  79      int fd;
  80      off_t length;
  81 {
  82   return chsize (fd, length);
  83 }
  84
  85 #else /* not F_CHSIZE nor F_FREESP nor HAVE_CHSIZE */
  86
  87 #include <errno.h>
  88 #ifndef errno
  89 extern int errno;
  90 #endif
  91
  92 int
  93 ftruncate (fd, length)
  94      int fd;
  95      off_t length;
  96 {
  97   errno = EIO;
  98   return -1;
  99 }
 100
 101 #endif /* not HAVE_CHSIZE */
 102 #endif /* not F_FREESP */
 103 #endif /* not F_CHSIZE */