[RFC, PATCH] xfs: make superblock version checks reflect reality

[Christoph Hellwig]

On Fri, Mar 07, 2014 at 07:34:30PM +1100, Dave Chinner wrote:
> Ok, we don't reject filesystems that don't have the NLINK bit set.
> Older filesystems that have only v1 inodes won't have that bit
> set, and we didn't set NLINK by default in mkfs until late 2007.
> Hence we need to keep some form of NLINK support around.
> 
> The alternative is to simply set the bit in the superblock if it is
> not set, and then just assume everywhere that it is set and we are
> using v2 inodes. That will get rid of the hasnlink/addnlink code
> needed to modify the superblock when the link count goes above
> MAX_NLINK_1, and will result in filesystems always converting v1
> inodes to v2 inodes on writeback of dirty inodes. I don't see a
> problem with taking this approach, bt maybe I'm missing something?

I'd love to get rid of v1 support sprinkled all over.  Obviously this
should be a separate patch, but making both the code and the in-use
filesystems less diverse is a good idea.