Re: What to do about subvolumes?

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Dec 01, 2010 at 03:09:52PM -0500, Josef Bacik wrote:
> On Wed, Dec 01, 2010 at 03:00:08PM -0500, J. Bruce Fields wrote:
> > On Wed, Dec 01, 2010 at 02:54:33PM -0500, Josef Bacik wrote:
> > > Oh well crud, I was hoping that I could leave the inode numbers as 256 for
> > > everything, but I forgot about readdir.  So the inode item in the parent would
> > > have to have a unique inode number that would get spit out in readdir, but then
> > > if we stat'ed the directory we'd get 256 for the inode number.  Oh well,
> > > incompat flag it is then.
> > 
> > I think you're already fine:
> > 
> > 	# mkdir TMP
> > 	# dd if=/dev/zero of=TMP-image bs=1M count=512
> > 	# mkfs.btrfs TMP-image
> > 	# mount -oloop TMP-image TMP/
> > 	# btrfs subvolume create sub-a
> > 	# btrfs subvolume create sub-b
> > 	../readdir-inos .
> > 	. 256 256
> > 	.. 256 4130609
> > 	sub-a 256 256
> > 	sub-b 257 256
> > 
> > Where readdir-inos is my silly test program below, and the first number is from
> > readdir, the second from stat.
> >
> 
> Heh as soon as I typed my email I went and actually looked at the code, looks
> like for readdir we fill in the root id, which will be unique, so hotdamn we are
> good and I don't have to use a stupid incompat flag.  Thanks for checking that
> :),

My only complaint was just about how you said this:

	"When you create a subvolume, the directory inode that is
	created in the parent subvolume has the inode number of 256"

If you revise that you might want to clarify.  (Maybe "Every subvolume
has a root directory inode with inode number 256"?)

The way you've stated it sounds like you're talking about the
readdir-returned number, which would normally come from the inode that
has been covered up by the mount, and which really is an inode in the
parent filesystem....

--b.