linux-kernel - Re: [PATCH 0/9] overlay filesystem: request for inclusion (v17)

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Date:	Fri, 15 Mar 2013 14:09:14 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, apw@...onical.com,
	nbd@...nwrt.org, neilb@...e.de, jordipujolp@...il.com,
	ezk@....cs.sunysb.edu, dhowells@...hat.com,
	sedat.dilek@...glemail.com, mszeredi@...e.cz
Subject: Re: [PATCH 0/9] overlay filesystem: request for inclusion (v17)


Al Viro:
> > +- whiteout is hardlinked in order to reduce the consumption of inodes
> > +  on branch
>
> *blink* Whiteouts have no inodes at all.  Filesystem has an additional
> kind of directory entries, recognizable as whiteouts.  How they are
> done is up to filesystem in question.

"no inodes at all"?
Are you assuming the implementation in dcache only (with a new d_type
flag)? And it is up to the real fs (layer or branch) whether it consumes
inode or not?
If so, it has a big disadvantage for the layer-fs (or branch-fs) to have
to implement a new method for whiteout.

Overlayfs implements whiteout as symlink+xattr which consumes an
inode. And you don't like it, right?
What I showed is another generic approach without xattr where the new
method to whiteout is unnecessary.


> > +The whiteout in aufs is very similar to Unionfs's. That is represented
> > +by its filename. UnionMount takes an approach of a file mode, but I am
> > +afraid several utilities (find(1) or something) will have to support it.
>
> Why the devil should find(1) even see them?

It is the case when find(1) for the layer-fs/branch-fs directly.


J. R. Okajima
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