[Dovecot] Avoiding Hardlinks (was: Something other than dotlock for uidlist locking?)

[James Berry]

Timo,

Thanks for your comments and attention. I'm attaching a patch which  
is a bit rough, but it's what I'm going to begin testing with.  
Basically in all cases ifdef'd based on AVOID_HARDLINKS. Hopefully  
you might be able to improve the configurability of the dotlock case.

Thanks for such a great product.

James

On Aug 9, 2006, at 3:05 PM, Timo Sirainen wrote:

> On 9.8.2006, at 23.44, James Berry wrote:
>> Timo, would you mind commenting on these to make sure my  
>> understanding is correct? And for the last one, I need a  
>> suggestion on how to proceed.
>>
>> file-copy.c:  [EASY]
>>
>> 	Looks like it would be easy to take the already coded case for  
>> when try_hardlink is false.
>
> Yes, easy. This case could even be #ifdefed. Although currently the  
> only user of file_copy() is copying ssl-parameters.dat from /var/ 
> lib/dovecot to /var/run/dovecot, and I don't see it being used  
> elsewhere anytime soon.

#ifdef'd

>> file-dotlock.c: [EASY]
>>
>> 	In dotlock_create, use try_create_lock_excl rather than  
>> try_create_lock_hardlink.
>
> This really should rather be configurable from dovecot.conf, but  
> there's no simple way to do that, except something like a getenv()  
> hack inside the file-dotlock.c code..
>
> I don't think this should be #ifdefed since O_EXCL could break if  
> you're using NFS.

#ifdef'd to always take the O_EXCL case if AVOID_HARDLINKS is defined.

>> maildir-copy.c: [LOOKS EASY]
>>
>> 	In maildir_copy(), take the fallback case using mail_storage_copy.
>
> This is the default (maildir_copy_with_hardlinks=no) so no need to  
> do anything.

Okay, nothing done.

>> maildir-save.c: [NEED HELP]
>>
>> 	In maildir_file_move(), there seems to be no fallback case, and  
>> I'm unsure of the desired  symantics, so I could use some  
>> suggestions here: can we just fall back into something like the  
>> code in file-copy.c?
>
> Like you noticed, this can be changed to just rename(). The only  
> reason it's link()+unlink() is because maildir spec says it should  
> be done like that. And in case the maildir filenames aren't really  
> unique the link()+unlink() method makes sure that mails aren't  
> overwritten, but that practically can't happen with Dovecot. This  
> code could perhaps also be #ifdefed..

#ifdef'd to always use rename() if AVOID_HARDLINKS is defined.

Patch attached:

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