Careful_atomic_create in atomic_create.c first creates a temporary
lock file that depends on the hostname.  It then attempts to hard link
it to the actual lock file.

If the filesystem doesn't support hard links (e.g. we're using FAT),
careful_atomic_create falls back to the sloppy strategy.

Interestingly, some people choose to have colons in the hostname of
their machine (which violates RFC 952 and has interesting side-effects
when using X).  In that case, creation of the temporary filename
fails, which causes grief and suffering.

The obvious fix is to shoot people who put colons in hostnames.

The other obvious fix is to replace all weird characters with dashes
in careful_atomic_create.

                                        Juliusz

jch recommended replacing "all weird characters" in careful_atomic create with
dashes. Which "weird characters" are being referred to here? Perhaps this
sprintf statement? 

    rc = snprintf(filename + dirlen, FILENAME_SIZE, "darcs_lock_%s%04x%04x",
                  hostname, ((unsigned)getpid()) & 0xFFFF,
                  ((unsigned)(now.tv_usec ^ (now.tv_usec >> 16))) & 0xFFFF);

On Wed, Jan 30, 2008 at 12:51:14AM -0000, Mark Stosberg wrote:
> jch recommended replacing "all weird characters" in careful_atomic create with
> dashes. Which "weird characters" are being referred to here? Perhaps this
> sprintf statement? 
> 
>     rc = snprintf(filename + dirlen, FILENAME_SIZE, "darcs_lock_%s%04x%04x",
>                   hostname, ((unsigned)getpid()) & 0xFFFF,
>                   ((unsigned)(now.tv_usec ^ (now.tv_usec >> 16))) & 0xFFFF);

That looks reasonable.
-- 
David Roundy
Department of Physics
Oregon State University

> jch recommended replacing "all weird characters" in careful_atomic create with
> dashes. Which "weird characters" are being referred to here? Perhaps this
> sprintf statement?

Yep.  Just after getting the hostname, do something like (untested):

  n = strlen(hostname);
  for(i = 0; i < n; i++) {
      c = hostname[i];
      if((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
         (c >= '0' && c <= '9') || c == '-' || c == '_')
          continue;
      hostname[i] = '-';
  }

                                        Juliusz