Re: [Dovecot] More AFS maildir debugging

24 Jan 2007


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"TS" == Timo Sirainen <tss@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@not-invented-here$ (cd /tmp; perl ~/tmp/t.PL;)
pod@not-invented-here$ (cd ~/afs/tmp; perl ~/tmp/t.PL;)
T1: Invalid cross-device link at /home/pod/tmp/t.PL line 34.
pod@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;