[Dovecot] More AFS maildir debugging

[pod]

>>>>> "TS" == Timo Sirainen <tss at iki.fi> writes:

    TS>  - create tmp file
    TS>  - link() to .lock file
    TS>  - unlink tmp file
    TS>  - write to .lock file
    TS>  - rename() to destination file

I think the problem here is that the rename will return EXDEV in a
cross-directory situation if the file in question is also being held open.
I think what is at the root of this behaviour is that AFS will buffer
writes on the client which get flushed on close.

At least this is the impression I get from running some nasty perl
(appended):

pod at not-invented-here$ (cd /tmp; perl ~/tmp/t.PL;)
pod at not-invented-here$ (cd ~/afs/tmp; perl ~/tmp/t.PL;)
T1: Invalid cross-device link at /home/pod/tmp/t.PL line 34.
pod at not-invented-here$ 

-------------------- barf now --------------------
#! /usr/bin/perl
use strict;
use warnings;
use POSIX qw(link unlink rename);

sub open_link_write_rename {
  my $s=shift;
  my $d=shift;

  open(F, ">$s") or die;
  link($s, $s.".lock") or die;
  unlink($s) or die;
  print(F scalar localtime, "\n") or die;
  rename($s.".lock", $d) or die;
}

sub open_link_write_close_rename {
  my $s=shift;
  my $d=shift;

  open(F, ">$s") or die;
  link($s, $s.".lock") or die;
  unlink($s) or die;
  print(F scalar localtime, "\n") or die;
  close(F) or die;
  rename($s.".lock", $d) or die;
}

mkdir "a" and mkdir "b" or die;

eval {
  open_link_write_rename("a/foo", "b/foo");
};
warn "T1: $!" if $@;
close(F) or warn "$!";
map {unlink $_} "a/foo", "a/foo.lock", "b/foo";

eval {
  open_link_write_close_rename("a/foo", "b/foo");
};
warn "T2: $!" if $@;
map {unlink $_} "a/foo", "a/foo.lock", "b/foo";

eval {
  open_link_write_rename("a/foo", "a/bar");
};
warn "T3: $!" if $@;
close(F) or warn "$!";
map {unlink $_} "a/foo", "a/foo.lock", "a/bar";

eval {
  open_link_write_close_rename("a/foo", "a/bar");
};
warn "T4: $!" if $@;
map {unlink $_} "a/foo", "a/foo.lock", "a/bar";

rmdir "a" and rmdir "b" or die;