lib/libc/posix/_getcwd.c

   1 /*      getcwd() - get the name of the current working directory.
   2  *                                                      Author: Kees J. Bot
   3  *                                                              30 Apr 1989
   4  */
   5 #define chdir _chdir
   6 #define closedir _closedir
   7 #define getcwd _getcwd
   8 #define opendir _opendir
   9 #define readdir _readdir
  10 #define rewinddir _rewinddir
  11 #define stat _stat
  12 #include <sys/types.h>
  13 #include <sys/stat.h>
  14 #include <errno.h>
  15 #include <unistd.h>
  16 #include <dirent.h>
  17 #include <limits.h>
  18 #include <string.h>
  19
  20 static int addpath(const char *path, char **ap, const char *entry)
  21 /* Add the name of a directory entry at the front of the path being built.
  22  * Note that the result always starts with a slash.
  23  */
  24 {
  25         const char *e= entry;
  26         char *p= *ap;
  27
  28         while (*e != 0) e++;
  29
  30         while (e > entry && p > path) *--p = *--e;
  31
  32         if (p == path) return -1;
  33         *--p = '/';
  34         *ap= p;
  35         return 0;
  36 }
  37
  38 static int recover(char *p)
  39 /* Undo all those chdir("..")'s that have been recorded by addpath.  This
  40  * has to be done entry by entry, because the whole pathname may be too long.
  41  */
  42 {
  43         int e= errno, slash;
  44         char *p0;
  45
  46         while (*p != 0) {
  47                 p0= ++p;
  48
  49                 do p++; while (*p != 0 && *p != '/');
  50                 slash= *p; *p= 0;
  51
  52                 if (chdir(p0) < 0) return -1;
  53                 *p= slash;
  54         }
  55         errno= e;
  56         return 0;
  57 }
  58
  59 char *getcwd(char *path, size_t size)
  60 {
  61         struct stat above, current, tmp;
  62         struct dirent *entry;
  63         DIR *d;
  64         char *p, *up, *dotdot;
  65         int cycle;
  66
  67         if (path == NULL || size <= 1) { errno= EINVAL; return NULL; }
  68
  69         p= path + size;
  70         *--p = 0;
  71
  72         if (stat(".", &current) < 0) return NULL;
  73
  74         while (1) {
  75                 dotdot= "..";
  76                 if (stat(dotdot, &above) < 0) { recover(p); return NULL; }
  77
  78                 if (above.st_dev == current.st_dev
  79                                         && above.st_ino == current.st_ino)
  80                         break;  /* Root dir found */
  81
  82                 if ((d= opendir(dotdot)) == NULL) { recover(p); return NULL; }
  83
  84                 /* Cycle is 0 for a simple inode nr search, or 1 for a search
  85                  * for inode *and* device nr.
  86                  */
  87                 cycle= above.st_dev == current.st_dev ? 0 : 1;
  88
  89                 do {
  90                         char name[3 + NAME_MAX + 1];
  91
  92                         tmp.st_ino= 0;
  93                         if ((entry= readdir(d)) == NULL) {
  94                                 switch (++cycle) {
  95                                 case 1:
  96                                         rewinddir(d);
  97                                         continue;
  98                                 case 2:
  99                                         closedir(d);
 100                                         errno= ENOENT;
 101                                         recover(p);
 102                                         return NULL;
 103                                 }
 104                         }
 105                         if (strcmp(entry->d_name, ".") == 0) continue;
 106                         if (strcmp(entry->d_name, "..") == 0) continue;
 107
 108                         switch (cycle) {
 109                         case 0:
 110                                 /* Simple test on inode nr. */
 111                                 if (entry->d_ino != current.st_ino) continue;
 112                                 /*FALL THROUGH*/
 113
 114                         case 1:
 115                                 /* Current is mounted. */
 116                                 strcpy(name, "../");
 117                                 strcpy(name+3, entry->d_name);
 118                                 if (stat(name, &tmp) < 0) continue;
 119                                 break;
 120                         }
 121                 } while (tmp.st_ino != current.st_ino
 122                                         || tmp.st_dev != current.st_dev);
 123
 124                 up= p;
 125                 if (addpath(path, &up, entry->d_name) < 0) {
 126                         closedir(d);
 127                         errno = ERANGE;
 128                         recover(p);
 129                         return NULL;
 130                 }
 131                 closedir(d);
 132
 133                 if (chdir(dotdot) < 0) { recover(p); return NULL; }
 134                 p= up;
 135
 136                 current= above;
 137         }
 138         if (recover(p) < 0) return NULL;        /* Undo all those chdir("..")'s. */
 139         if (*p == 0) *--p = '/';        /* Cwd is "/" if nothing added */
 140         if (p > path) strcpy(path, p);  /* Move string to start of path. */
 141         return path;
 142 }