sysdeps/unix/sysv/linux/getcwd.c

   1 /* Determine current working directory.  Linux version.
   2    Copyright (C) 1997-2014 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <limits.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <sys/param.h>
  26
  27 #include <sysdep.h>
  28 #include <sys/syscall.h>
  29
  30 #include <kernel-features.h>
  31
  32
  33 /* If we compile the file for use in ld.so we don't need the feature
  34    that getcwd() allocates the buffers itself.  */
  35 #ifdef IS_IN_rtld
  36 # define NO_ALLOCATION  1
  37 #endif
  38
  39
  40 /* The "proc" filesystem provides an easy method to retrieve the value.
  41    For each process, the corresponding directory contains a symbolic link
  42    named `cwd'.  Reading the content of this link immediate gives us the
  43    information.  But we have to take care for systems which do not have
  44    the proc filesystem mounted.  Use the POSIX implementation in this case.  */
  45 static char *generic_getcwd (char *buf, size_t size) internal_function;
  46
  47 char *
  48 __getcwd (char *buf, size_t size)
  49 {
  50   char *path;
  51   char *result;
  52
  53 #ifndef NO_ALLOCATION
  54   size_t alloc_size = size;
  55   if (size == 0)
  56     {
  57       if (buf != NULL)
  58         {
  59           __set_errno (EINVAL);
  60           return NULL;
  61         }
  62
  63       alloc_size = MAX (PATH_MAX, __getpagesize ());
  64     }
  65
  66   if (buf == NULL)
  67     {
  68       path = malloc (alloc_size);
  69       if (path == NULL)
  70         return NULL;
  71     }
  72   else
  73 #else
  74 # define alloc_size size
  75 #endif
  76     path = buf;
  77
  78   int retval;
  79
  80   retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
  81   if (retval >= 0)
  82     {
  83 #ifndef NO_ALLOCATION
  84       if (buf == NULL && size == 0)
  85         /* Ensure that the buffer is only as large as necessary.  */
  86         buf = realloc (path, (size_t) retval);
  87
  88       if (buf == NULL)
  89         /* Either buf was NULL all along, or `realloc' failed but
  90            we still have the original string.  */
  91         buf = path;
  92 #endif
  93
  94       return buf;
  95     }
  96
  97   /* The system call cannot handle paths longer than a page.
  98      Neither can the magic symlink in /proc/self.  Just use the
  99      generic implementation right away.  */
 100   if (errno == ENAMETOOLONG)
 101     {
 102 #ifndef NO_ALLOCATION
 103       if (buf == NULL && size == 0)
 104         {
 105           free (path);
 106           path = NULL;
 107         }
 108 #endif
 109
 110       result = generic_getcwd (path, size);
 111
 112 #ifndef NO_ALLOCATION
 113       if (result == NULL && buf == NULL && size != 0)
 114         free (path);
 115 #endif
 116
 117       return result;
 118     }
 119
 120   /* It should never happen that the `getcwd' syscall failed because
 121      the buffer is too small if we allocated the buffer ourselves
 122      large enough.  */
 123   assert (errno != ERANGE || buf != NULL || size != 0);
 124
 125 #ifndef NO_ALLOCATION
 126   if (buf == NULL)
 127     free (path);
 128 #endif
 129
 130   return NULL;
 131 }
 132 weak_alias (__getcwd, getcwd)
 133
 134 /* Get the code for the generic version.  */
 135 #define GETCWD_RETURN_TYPE      static char * internal_function
 136 #define __getcwd                generic_getcwd
 137 #include <sysdeps/posix/getcwd.c>