Re: [PATCH 0/2] xfs: defrag support for v5 filesystems

Ben Myers
2013-09-03T19:12:04Z

Hey Dave,

On Fri, Aug 30, 2013 at 10:23:43AM +1000, Dave Chinner wrote:
> Hi folks,
>
> The following 2 patches implement the BMBT owner change transaction
> that is necessary to enable the XFS_IOC_SWAPEXT ioctl to operate on
> v5 filesystems correctly. The first patch implements the
> transactional runtime change, and the second patch implements the
> recovery of that change.
>
> Both the run time and recovery code use the same mechanism for
> changing the owner field in all the blocks in the BMBT on an inode,
> and even though XFS_IOC_SWAPEXT only swaps the data fork, the code
> has been written to be fork neutral so if we even need to swap
> attribute forks it should just work for that, too.
>
> Further, because the BMBT code uses the generic btree
> infrastructure, the btree modification is done as a generic function
> as well and so should work for all types of btrees supported by the
> generic code. Hence if the need arises we can easily change the
> owner of any btree that uses the generic code.
>
> The testing carried out is documented in the description of the
> second patch.
>
> AFAIA, this is the only remaining feature that the kernel v5
> filesystem implementation didn't support. Hence, with this patchset,
> there are no more feature checkboxes that need to be ticked that
> would prevent us from removing the experimental tag from it. Testing
> is the only remaining gate to removing the tag from the kernel
> code...

I believe there is still the discussion surrounding being able to use
the self describing metadata without enabling crcs that needs to be
resolved before removing the experimental tag. Some customers will want
to use features such as t10-dif and won't want to calculate two separate
crcs. Normally that discussion probably needn't gate the removal of the
experimental tag, but unfortunately there will be some compatability
issues surrounding an additional feature bit and modification of mkfs
that we should probably iron out first.

Other than that discussion, I think we're about on the same page...

Regards,
Ben