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#include <errno.h>

#include <sys/stat.h>

#include <dirent.h>

#include <string.h>

/*

 * These functions find the absolute path to the current working directory.

 *

 * They don't use malloc or large amounts of stack space.

 */

static char * recurser();       /* Routine to go up tree */

static char * search_dir();     /* Routine to find the step back down */

static char * path_buf;

static int    path_size;

static dev_t root_dev;

static ino_t root_ino;

static struct stat st;

char *

getcwd(buf, size)

char * buf;

int size;

{

   path_buf = buf;

   path_size = size;

   if( size < 3 ) { errno = ERANGE; return 0; }

   strcpy(path_buf, ".");

   if( stat("/", &st) < 0 ) return 0;

   root_dev = st.st_dev;

   root_ino = st.st_ino;

   return recurser();

}

static char *

recurser()

{

   dev_t this_dev;

   ino_t this_ino;

   if( stat(path_buf, &st) < 0 ) return 0;

   this_dev = st.st_dev;

   this_ino = st.st_ino;

   if( this_dev == root_dev && this_ino == root_ino )

   {

      strcpy(path_buf, "/");

      return path_buf;

   }

   if( strlen(path_buf) + 4 > path_size ) { errno = ERANGE; return 0; }

   strcat(path_buf, "/..");

   if( recurser() == 0 ) return 0;

   return search_dir(this_dev, this_ino);

}

static char *

search_dir(this_dev, this_ino)

dev_t this_dev;

ino_t this_ino;

{

   DIR * dp;

   struct dirent * d;

   char * ptr;

   int slen;

   /* The test is for ELKS lib 0.0.9, this should be fixed in the real kernel*/

   int slow_search = (sizeof(ino_t) != sizeof(d->d_ino));

   if( stat(path_buf, &st) < 0 ) return 0;

   if( this_dev != st.st_dev ) slow_search = 1;

   slen = strlen(path_buf);

   ptr = path_buf + slen -1;

   if( *ptr != '/' )

   {

      if( slen + 2 > path_size ) { errno = ERANGE; return 0; }

      strcpy(++ptr, "/");

      slen++;

   }

   slen++;

   dp = opendir(path_buf);

   if( dp == 0 ) return 0;

   while( (d=readdir(dp)) != 0 )

   {

      if( slow_search || this_ino == d->d_ino )

      {

         if( slen + strlen(d->d_name) > path_size )

            { errno = ERANGE; return 0; }

         strcpy(ptr+1, d->d_name);

         if( stat(path_buf, &st) < 0 )

            continue;

         if( st.st_ino == this_ino && st.st_dev == this_dev )

         {

            closedir(dp);

            return path_buf;

         }

      }

   }

   closedir(dp);

   errno = ENOENT;

   return 0;

}