Function force_symlinkat

src/force-link.c:151–184

Create a symlink containing SRCNAME in directory DSTDIR's file DSTNAME. If FORCE and DSTNAME already exists, replace it atomically. If SYMLINKAT_ERRNO is 0, the symlink is already done; if positive, the symlink was tried and failed with errno == SYMLINKAT_ERRNO. Return -1 if successful and DSTNAME already existed, 0 if successful and DSTNAME did not already exist, and a positive

   0 if successful and DSTNAME did not already exist, and
   a positive errno value on failure.  */
extern int
force_symlinkat (char const *srcname, int dstdir, char const *dstname,
                 bool force, int symlinkat_errno)
{
  if (symlinkat_errno < 0)
    symlinkat_errno = symlinkat (srcname, dstdir, dstname) == 0 ? 0 : errno;
  if (!force || symlinkat_errno != EEXIST)
    return symlinkat_errno;

  char buf[smallsize];
  char *dsttmp = samedir_template (dstname, buf);
  if (!dsttmp)
    return errno;
  struct symlink_arg arg = { srcname, dstdir };
  int err;

  if (try_tempname_len (dsttmp, 0, &arg, try_symlink, x_suffix_len) != 0)
    err = errno;
  else if (renameat (dstdir, dsttmp, dstdir, dstname) != 0)
    {
      err = errno;
      unlinkat (dstdir, dsttmp, 0);
    }
  else
    {
      /* Don't worry about renameat being a no-op, since DSTTMP is
         newly created.  */
      err = -1;
    }

  if (dsttmp != buf)
    free (dsttmp);
  return err;
}