Re: syncing a directory

[Jason Thorpe <thorpej%shagadelic.org@localhost>]

On Jul 9, 2008, at 9:40 AM, Edgar Fuß wrote:

> Is there a way (other than sync()) to make sure a rename() has made  
> it to non-volatile storage?
>
> Dovecot wants to be sure that having moved a file from (maildir)  
> tmp/ to new/ is going to survive a crash before reporting success to  
> the client. The (possible Linuxish) way it attempts to do this is to  
> open the directory (O_RDONLY, of course) and then fsync()ing the  
> file handle. Set aside the question whether this does anything  
> useful on Linux, NetBSD objects, presumably because fsync() on a  
> read-only descriptor doesn't make sense.
>
> I know well that metadata writes used to be synchronous anyway, but  
> they are no more in the age of soft updates.

It's not in non-volatile storage unless you also tell the disk to  
flush its cache.  NetBSD does not currently have a file descriptor- 
based API to do that.

> It looks reasonable what dovecot demands, and it seems reasonable  
> NetBSD objects to the specific way it tries doing that. But what  
> would be the correct way of doing it? What if the files in question  
> reside on NFS?

-- thorpej