Re: [PATCH v2] btrfs-progs: support free space tree in mkfs

[Boris Burkov <boris@bur.io>]

On Tue, Sep 08, 2020 at 09:55:59PM +0200, David Sterba wrote:
> On Thu, Sep 03, 2020 at 11:19:23AM -0700, Boris Burkov wrote:
> > Add a runtime feature (-R) flag for the free space tree. A filesystem
> > that is mkfs'd with -R free-space-tree then mounted with no options has
> > the same contents as one mkfs'd without the option, then mounted with
> > '-o space_cache=v2'.
> > 
> > The only tricky thing is in exactly how to call the tree creation code.
> > Using btrfs_create_free_space_tree as is did not quite work, because an
> > extra reference to the eb (root->commit_root) is leaked, which mkfs
> > complains about with a warning. I opted to follow how the uuid tree is
> > created by adding it to the dirty roots list for cleanup by
> > commit_tree_roots in commit_transaction. As a result,
> > btrfs_create_free_space_tree no longer exactly matches the version in
> > the kernel sources.
> > 
> > Signed-off-by: Boris Burkov <boris@bur.io>
> > ---
> > - add mkfs test
> > - add documentation
> > - add safe version and sysfs file to feature struct
> > 
> >  Documentation/mkfs.btrfs.asciidoc            |  6 ++++++
> >  common/fsfeatures.c                          | 10 ++++++++--
> >  common/fsfeatures.h                          |  3 ++-
> >  kernel-shared/disk-io.c                      |  5 +++++
> >  kernel-shared/free-space-tree.c              |  1 +
> >  mkfs/main.c                                  |  8 ++++++++
> >  tests/mkfs-tests/023-free-space-tree/test.sh | 21 ++++++++++++++++++++
> >  7 files changed, 51 insertions(+), 3 deletions(-)
> >  create mode 100755 tests/mkfs-tests/023-free-space-tree/test.sh
> > 
> > diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc
> > index 630f575c..8f1e1429 100644
> > --- a/Documentation/mkfs.btrfs.asciidoc
> > +++ b/Documentation/mkfs.btrfs.asciidoc
> > @@ -257,6 +257,12 @@ permanent, this does not replace mount options.
> >  Enable quota support (qgroups). The qgroup accounting will be consistent,
> >  can be used together with '--rootdir'.  See also `btrfs-quota`(8).
> >  
> > +*free_space_tree*::
> > +(kernel support since 3.4)
> > ++
> > +Enable the free space tree (mount option space_cache=v2) for persisting the
> > +free space cache.
> > +
> >  BLOCK GROUPS, CHUNKS, RAID
> >  --------------------------
> >  
> > diff --git a/common/fsfeatures.c b/common/fsfeatures.c
> > index 48ab37ca..6c391806 100644
> > --- a/common/fsfeatures.c
> > +++ b/common/fsfeatures.c
> > @@ -104,9 +104,15 @@ static const struct btrfs_feature mkfs_features[] = {
> >  };
> >  
> >  static const struct btrfs_feature runtime_features[] = {
> > -	{ "quota", BTRFS_RUNTIME_FEATURE_QUOTA, NULL,
> > -		VERSION_TO_STRING2(3, 4), NULL, 0, NULL, 0,
> > +	{ "quota", BTRFS_RUNTIME_FEATURE_QUOTA,
> > +		"free_space_tree",
> > +		VERSION_TO_STRING2(3, 4),
> > +		VERSION_TO_STRING2(4, 9),
> > +		NULL, 0,
> 
> This looks mangled, the free_space_tree (sysfs file reference) is in the
> quota entry and the 4.9 version for ->safe use should be in the free-space-tree
> entry below. I'll fix it.
> 

My mistake! I'm very sorry for the sloppy patch. Thanks for fixing it.

> >  		"quota support (qgroups)" },
> > +	{ "free-space-tree", BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE, NULL,
> > +		VERSION_TO_STRING2(4, 5), NULL, 0, NULL, 0,
> > +		"free space tree (space_cache=v2)" },
> 
> >  	/* Keep this one last */
> >  	{ "list-all", BTRFS_FEATURE_LIST_ALL, NULL }
> >  };