linux-kernel - Re: [PULL for 3.18] overlay filesystem v24

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Message-ID: <27645.1412052879@jrobl>
Date:	Tue, 30 Sep 2014 13:54:39 +0900
From:	"J. R. Okajima" <hooanon05g@...il.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-unionfs@...r.kernel.org
Subject: Re: [PULL for 3.18] overlay filesystem v24


David Howells:
> Miklos Szeredi <miklos@...redi.hu> wrote:
>
> > I'd like to propose overlayfs for inclusion into 3.18.
> > 
> > Al, would you mind giving it a review?
> > 
> > Git tree is here:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git overlayfs.current
>
> Tested-by: David Howells <dhowells@...hat.com>

Does it mean overlayfs passed all your unionmount-testsuite? And does
the test suite contain tests for "inode-based" union? For example,
- read(2) may get the obsoleted filedata (fstat(2) for metadata too).
- fcntl(F_SETLK) may be broken by copy-up.
- inotify may not work when it refers to the file before being
  copied-up.
- unnecessary copy-up may happen, for example mmap(MAP_PRIVATE) after
  open(O_RDWR).
- exporting via NFS and fhandle systemcalls will not work.

A few releases ago, OFD file-lock was introduced to improve the
behaviour of POSIX lock. POSIX lock has made users confused and I am
afraid that the similar story will come up because of the "name-based"
union behaviour. Of course the story is not limited to the file-lock.

If I remember correctly, are you the one who consitunes the development
of UnionMount? Is the development totally stopped?
Next paragraph is what I wrote several times.
	AUFS is an "inode-based" stackable filesystem and solved them many years
	ago. But I have to admit that AUFS is big. Yes it is grown up.
	I don't stop including overlayfs into mainline, but if the development
	of UnionMount is really stopped, then I'd ask people to consider merging
	aufs as well as overlayfs.

http://aufs.sf.net

J. R. Okajima
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