sysdeps/unix/sysv/linux/getcwd.c

   1 /* Determine current working directory.  Linux version.
   2    Copyright (C) 1997-2018 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
  31 /* If we compile the file for use in ld.so we don't need the feature
  32    that getcwd() allocates the buffers itself.  */
  33 #if IS_IN (rtld)
  34 # define NO_ALLOCATION  1
  35 #endif
  36
  37
  38 /* The "proc" filesystem provides an easy method to retrieve the value.
  39    For each process, the corresponding directory contains a symbolic link
  40    named `cwd'.  Reading the content of this link immediate gives us the
  41    information.  But we have to take care for systems which do not have
  42    the proc filesystem mounted.  Use the POSIX implementation in this case.  */
  43 static char *generic_getcwd (char *buf, size_t size);
  44
  45 char *
  46 __getcwd (char *buf, size_t size)
  47 {
  48   char *path;
  49   char *result;
  50
  51 #ifndef NO_ALLOCATION
  52   size_t alloc_size = size;
  53   if (size == 0)
  54     {
  55       if (buf != NULL)
  56         {
  57           __set_errno (EINVAL);
  58           return NULL;
  59         }
  60
  61       alloc_size = MAX (PATH_MAX, __getpagesize ());
  62     }
  63
  64   if (buf == NULL)
  65     {
  66       path = malloc (alloc_size);
  67       if (path == NULL)
  68         return NULL;
  69     }
  70   else
  71 #else
  72 # define alloc_size size
  73 #endif
  74     path = buf;
  75
  76   int retval;
  77
  78   retval = INLINE_SYSCALL (getcwd, 2, path, alloc_size);
  79   if (retval > 0 && path[0] == '/')
  80     {
  81 #ifndef NO_ALLOCATION
  82       if (buf == NULL && size == 0)
  83         /* Ensure that the buffer is only as large as necessary.  */
  84         buf = realloc (path, (size_t) retval);
  85
  86       if (buf == NULL)
  87         /* Either buf was NULL all along, or `realloc' failed but
  88            we still have the original string.  */
  89         buf = path;
  90 #endif
  91
  92       return buf;
  93     }
  94
  95   /* The system call either cannot handle paths longer than a page
  96      or can succeed without returning an absolute path.  Just use the
  97      generic implementation right away.  */
  98   if (retval >= 0 || errno == ENAMETOOLONG)
  99     {
 100 #ifndef NO_ALLOCATION
 101       if (buf == NULL && size == 0)
 102         {
 103           free (path);
 104           path = NULL;
 105         }
 106 #endif
 107
 108       result = generic_getcwd (path, size);
 109
 110 #ifndef NO_ALLOCATION
 111       if (result == NULL && buf == NULL && size != 0)
 112         free (path);
 113 #endif
 114
 115       return result;
 116     }
 117
 118   /* It should never happen that the `getcwd' syscall failed because
 119      the buffer is too small if we allocated the buffer ourselves
 120      large enough.  */
 121   assert (errno != ERANGE || buf != NULL || size != 0);
 122
 123 #ifndef NO_ALLOCATION
 124   if (buf == NULL)
 125     free (path);
 126 #endif
 127
 128   return NULL;
 129 }
 130 weak_alias (__getcwd, getcwd)
 131
 132 /* Get the code for the generic version.  */
 133 #define GETCWD_RETURN_TYPE      static char *
 134 #define __getcwd                generic_getcwd
 135 #include <sysdeps/posix/getcwd.c>