Re: Ext4 devel interlock meeting minutes (Nov. 22 2006)

[Eric Sandeen <sandeen@redhat.com>]

Avantika Mathur wrote:
> Ext4 Developer Interlock Call: 11/22/06 minutes
> 
> Attendees: Mingming Cao, Eric Sandeen, Suparna Bhattacharya, Takashi Sato, Jean-Pierre Dion, Valérie Clément, Avantika Mathur
> 
> - Online Defrag:
>  -- Last week we determined that ioctl was the preferred 
> interface for the online defrag.
>  -- Eric will send out an ovreview of the steps completed by XFS for file defragmentation.
>  -- Last week Eric said that in XFS defrag implementation, you can't defrag a file that is open/being written to.  This was an incorrect assumption. There will be more explanation in his mail.
> 
> - Preallocation:
>  -- We need to decide which interface to use in the implementation
>    * ioctl: simple solution preferred method for defrag and user in reservation

And would also be useful for testing, at least.  If reiserfs or jfs or 
xfs has existing interfaces for preallocation that are at all useful, 
perhaps we could even piggyback on them for now, in the same way that 
other filesystems picked up ext[23]'s chattr interfaces?

>    * posix_fallocate: writes zero to the first byte of every block; probably preferred solution

For the record, this is only how glibc does it today, it certainly 
doesn't have to be done this way, ideally a kernel syscall which allows 
filesystems to be smart would be best.  Coordinating glibc & kernel 
changes will be tricky & time consuming though... but it's a noble goal. 
  I'd like to see it happen; I'll chat with Ulrich when I get a chance, 
see what he thinks.

>    * ftruncate: consistency across platforms may be an issue

I agree w/ Andreas on this, I don't see how ftruncate can be used w/o 
making holey files impossible.

-Eric