macro and text revision (-mdoc version 3)

[unix-history] / usr / src / lib / libc / gen / getcwd.c

/*
* Copyright (c) 1989, 1991 The Regents of the University of California.
* All rights reserved.
*
* %sccs.include.redist.c%
*/

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)getcwd.c    5.11 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <sys/param.h>
#include <sys/stat.h>
#include <errno.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define ISDOT(dp) \
       (dp->d_name[0] == '.' && (dp->d_name[1] == '\0' || \
           dp->d_name[1] == '.' && dp->d_name[2] == '\0'))

char *
getcwd(pt, size)
       char *pt;
       size_t size;
{
       register struct dirent *dp;
       register DIR *dir;
       register dev_t dev;
       register ino_t ino;
       register int first;
       register char *bpt, *bup;
       struct stat s;
       dev_t root_dev;
       ino_t root_ino;
       size_t ptsize, upsize;
       int save_errno;
       char *ept, *eup, *up;

       /*
        * If no buffer specified by the user, allocate one as necessary.
        * If a buffer is specified, the size has to be non-zero.  The path
        * is built from the end of the buffer backwards.
        */
       if (pt) {
               ptsize = 0;
               if (!size) {
                       errno = EINVAL;
                       return((char *)NULL);
               }
               ept = pt + size;
       } else {
               if (!(pt = (char *)malloc(ptsize = 1024 - 4)))
                       return((char *)NULL);
               ept = pt + ptsize;
       }
       bpt = ept - 1;
       *bpt = '\0';

       /*
        * Allocate bytes (1024 - malloc space) for the string of "../"'s.
        * Should always be enough (it's 340 levels).  If it's not, allocate
        * as necessary.  Special * case the first stat, it's ".", not "..".
        */
       if (!(up = (char *)malloc(upsize = 1024 - 4)))
               goto err;
       eup = up + MAXPATHLEN;
       bup = up;
       up[0] = '.';
       up[1] = '\0';

       /* Save root values, so know when to stop. */
       if (stat("/", &s))
               goto err;
       root_dev = s.st_dev;
       root_ino = s.st_ino;

       errno = 0;                      /* XXX readdir has no error return. */

       for (first = 1;; first = 0) {
               /* Stat the current level. */
               if (lstat(up, &s))
                       goto err;

               /* Save current node values. */
               ino = s.st_ino;
               dev = s.st_dev;

               /* Check for reaching root. */
               if (root_dev == dev && root_ino == ino) {
                       *--bpt = '/';
                       /*
                        * It's unclear that it's a requirement to copy the
                        * path to the beginning of the buffer, but it's always
                        * been that way and stuff would probably break.
                        */
                       (void)bcopy(bpt, pt, ept - bpt);
                       free(up);
                       return(pt);
               }

               /*
                * Build pointer to the parent directory, allocating memory
                * as necessary.  Max length is 3 for "../", the largest
                * possible component name, plus a trailing NULL.
                */
               if (bup + 3  + MAXNAMLEN + 1 >= eup) {
                       if (!(up = (char *)realloc(up, upsize *= 2)))
                               goto err;
                       eup = up + upsize;
               }
               *bup++ = '.';
               *bup++ = '.';
               *bup = '\0';

               /* Open and stat parent directory. */
               if (!(dir = opendir(up)) || fstat(dirfd(dir), &s))
                       goto err;

               /* Add trailing slash for next directory. */
               *bup++ = '/';

               /*
                * If it's a mount point, have to stat each element because
                * the inode number in the directory is for the entry in the
                * parent directory, not the inode number of the mounted file.
                */
               save_errno = 0;
               if (s.st_dev == dev) {
                       for (;;) {
                               if (!(dp = readdir(dir)))
                                       goto notfound;
                               if (dp->d_fileno == ino)
                                       break;
                       }
               } else
                       for (;;) {
                               if (!(dp = readdir(dir)))
                                       goto notfound;
                               if (ISDOT(dp))
                                       continue;
                               bcopy(dp->d_name, bup, dp->d_namlen + 1);

                               /* Save the first error for later. */
                               if (lstat(up, &s)) {
                                       if (!save_errno)
                                               save_errno = errno;
                                       errno = 0;
                                       continue;
                               }
                               if (s.st_dev == dev && s.st_ino == ino)
                                       break;
                       }

               /*
                * Check for length of the current name, preceding slash,
                * leading slash.
                */
               if (bpt - pt <= dp->d_namlen + (first ? 1 : 2)) {
                       size_t len, off;

                       if (!ptsize) {
                               errno = ERANGE;
                               goto err;
                       }
                       off = bpt - pt;
                       len = ept - bpt;
                       if (!(pt = (char *)realloc(pt, ptsize *= 2)))
                               goto err;
                       bpt = pt + off;
                       ept = pt + ptsize;
                       (void)bcopy(bpt, ept - len, len);
                       bpt = ept - len;
               }
               if (!first)
                       *--bpt = '/';
               bpt -= dp->d_namlen;
               bcopy(dp->d_name, bpt, dp->d_namlen);
               (void)closedir(dir);

               /* Truncate any file name. */
               *bup = '\0';
       }

notfound:
       /*
        * If readdir set errno, use it, not any saved error; otherwise,
        * didn't find the current directory in its parent directory, set
        * errno to ENOENT.
        */
       if (!errno)
               errno = save_errno ? save_errno : ENOENT;
       /* FALLTHROUGH */
err:
       if (ptsize)
               free(pt);
       free(up);
       return((char *)NULL);
}