libio/iofdopen.c

   1 /* Copyright (C) 1993-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include <stdlib.h>
  28 #include "libioP.h"
  29 #include <fcntl.h>
  30
  31 #include <shlib-compat.h>
  32
  33 FILE *
  34 _IO_new_fdopen (int fd, const char *mode)
  35 {
  36   int read_write;
  37   struct locked_FILE
  38   {
  39     struct _IO_FILE_plus fp;
  40 #ifdef _IO_MTSAFE_IO
  41     _IO_lock_t lock;
  42 #endif
  43     struct _IO_wide_data wd;
  44   } *new_f;
  45   int i;
  46   int use_mmap = 0;
  47
  48   /* Decide whether we modify the offset of the file we attach to and seek to
  49      the end of file.  We only do this if the mode is 'a' and if the file
  50      descriptor did not have O_APPEND in its flags already.  */
  51   bool do_seek = false;
  52
  53   switch (*mode)
  54     {
  55     case 'r':
  56       read_write = _IO_NO_WRITES;
  57       break;
  58     case 'w':
  59       read_write = _IO_NO_READS;
  60       break;
  61     case 'a':
  62       read_write = _IO_NO_READS|_IO_IS_APPENDING;
  63       break;
  64     default:
  65       __set_errno (EINVAL);
  66       return NULL;
  67   }
  68   for (i = 1; i < 5; ++i)
  69     {
  70       switch (*++mode)
  71         {
  72         case '\0':
  73           break;
  74         case '+':
  75           read_write &= _IO_IS_APPENDING;
  76           break;
  77         case 'm':
  78           use_mmap = 1;
  79           continue;
  80         case 'x':
  81         case 'b':
  82         default:
  83           /* Ignore */
  84           continue;
  85         }
  86       break;
  87     }
  88   int fd_flags = __fcntl (fd, F_GETFL);
  89   if (fd_flags == -1)
  90     return NULL;
  91
  92   if (((fd_flags & O_ACCMODE) == O_RDONLY && !(read_write & _IO_NO_WRITES))
  93       || ((fd_flags & O_ACCMODE) == O_WRONLY && !(read_write & _IO_NO_READS)))
  94     {
  95       __set_errno (EINVAL);
  96       return NULL;
  97     }
  98
  99   /* The May 93 draft of P1003.4/D14.1 (redesignated as 1003.1b)
 100      [System Application Program Interface (API) Amendment 1:
 101      Realtime Extensions], Rationale B.8.3.3
 102      Open a Stream on a File Descriptor says:
 103
 104          Although not explicitly required by POSIX.1, a good
 105          implementation of append ("a") mode would cause the
 106          O_APPEND flag to be set.
 107
 108      (Historical implementations [such as Solaris2] do a one-time
 109      seek in fdopen.)
 110
 111      However, we do not turn O_APPEND off if the mode is "w" (even
 112      though that would seem consistent) because that would be more
 113      likely to break historical programs.
 114      */
 115   if ((read_write & _IO_IS_APPENDING) && !(fd_flags & O_APPEND))
 116     {
 117       do_seek = true;
 118       if (__fcntl (fd, F_SETFL, fd_flags | O_APPEND) == -1)
 119         return NULL;
 120     }
 121
 122   new_f = (struct locked_FILE *) malloc (sizeof (struct locked_FILE));
 123   if (new_f == NULL)
 124     return NULL;
 125 #ifdef _IO_MTSAFE_IO
 126   new_f->fp.file._lock = &new_f->lock;
 127 #endif
 128   _IO_no_init (&new_f->fp.file, 0, 0, &new_f->wd,
 129 #if _G_HAVE_MMAP
 130                (use_mmap && (read_write & _IO_NO_WRITES))
 131                ? &_IO_wfile_jumps_maybe_mmap :
 132 #endif
 133                &_IO_wfile_jumps);
 134   _IO_JUMPS (&new_f->fp) =
 135 #if _G_HAVE_MMAP
 136     (use_mmap && (read_write & _IO_NO_WRITES)) ? &_IO_file_jumps_maybe_mmap :
 137 #endif
 138       &_IO_file_jumps;
 139   _IO_new_file_init_internal (&new_f->fp);
 140   /* We only need to record the fd because _IO_file_init_internal will
 141      have unset the offset.  It is important to unset the cached
 142      offset because the real offset in the file could change between
 143      now and when the handle is activated and we would then mislead
 144      ftell into believing that we have a valid offset.  */
 145   new_f->fp.file._fileno = fd;
 146   new_f->fp.file._flags &= ~_IO_DELETE_DONT_CLOSE;
 147
 148   _IO_mask_flags (&new_f->fp.file, read_write,
 149                   _IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING);
 150
 151   /* For append mode, set the file offset to the end of the file if we added
 152      O_APPEND to the file descriptor flags.  Don't update the offset cache
 153      though, since the file handle is not active.  */
 154   if (do_seek && ((read_write & (_IO_IS_APPENDING | _IO_NO_READS))
 155                   == (_IO_IS_APPENDING | _IO_NO_READS)))
 156     {
 157       off64_t new_pos = _IO_SYSSEEK (&new_f->fp.file, 0, _IO_seek_end);
 158       if (new_pos == _IO_pos_BAD && errno != ESPIPE)
 159         return NULL;
 160     }
 161   return &new_f->fp.file;
 162 }
 163 libc_hidden_ver (_IO_new_fdopen, _IO_fdopen)
 164
 165 strong_alias (_IO_new_fdopen, __new_fdopen)
 166 versioned_symbol (libc, _IO_new_fdopen, _IO_fdopen, GLIBC_2_1);
 167 versioned_symbol (libc, __new_fdopen, fdopen, GLIBC_2_1);