Re: [PATCH 00/20] btrfs-progs: extent tree v2 global root support prep work

[Josef Bacik <josef@toxicpanda.com>]

On Sat, Nov 06, 2021 at 08:55:21AM +0800, Qu Wenruo wrote:
> 
> 
> On 2021/11/6 04:28, Josef Bacik wrote:
> > Hello,
> > 
> > This is a series of patches to do all the prep work needed to support extent
> > tree v2.  These patches are independent of the actual extent tree v2 support,
> > some of them are fixes,
> 
> First half are mostly good, as they are really fixes and independent
> refactors.
> 
> > some of them are purely to pave the way for the global
> > root support.  These patches are mostly around stopping direct access of
> > ->extent_root/->csum_root/->free_space_root, putting these roots into a rb_tree,
> > and changing the code to look up the roots in the rb_tree instead of accessing
> > them directly.  There are a variety of fixes to help make this easier, mostly
> > removing access to these roots that are strictly necessary.  Thanks,
> 
> But the later part for indirect access to previously global trees are
> somewhat questionable.
> 
> The idea of rb-tree caching these trees are no problem, but the callers
> are still passing place holder values to these helpers.
> 
> For current extent-tree, we can pass whatever values and get the root we
> want, but that also means, we need another round of patches to fix all
> the place holders to make them really extent-tree-v2 compatible.
> 
> Thus I'd prefer to see these helpers are called in a proper way in one
> go, which is not really feasible to test in current preparation form.
> 
> Maybe it would be better to put these patches with the real
> extent-tree-v2 code?
>

There's simply too much.  Basically anywhere btrfs_extent_root(fs_info, 0) needs
to be looked at to make sure it's compatible, and trust me I have a loooooot of
patches fixing up the different things that require special handling, and each
of them are beefy by themselves.

It makes it easier for reviewers to grok this way, there's no change for the
!extent_tree_v2 case, and then as the extent tree v2 stuff gets added I make the
necessary changes so they can be properly checked, because lord knows we
probalby fucked some of them up.  Thanks,

Josef