linux-kernel - Re: [overlayfs/port] overlayfs: v13 port attempt to kernel 3.5

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Date:	Mon, 20 Aug 2012 13:26:46 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	Andrew Watts <akwatts@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Daniel Baumann <daniel@...ian.org>
Subject: Re: [overlayfs/port] overlayfs: v13 port attempt to kernel 3.5

On Mon, Aug 20, 2012 at 12:38 PM, J. R. Okajima <hooanon05@...oo.co.jp> wrote:
>
> Sedat Dilek:
>> The other part to run a Linux live-system is a "Union FileSystem" -
>> this part is missing (speaking of upstream).
>>
>> Since years AUFS seems to be the choice #1 in a lot of distros to
>> workaround the problem.
>> NOTE: AUFS was rejected from upstream (to say not accepted).
>
> Exactly.
> The reason was that linux rejects all union-type filesystems but
> UnionMount (which is union-type mount).
> Later, the development of UnionMount seems to be almost stopped. The
> essential design of overlayfs is based upon UnionMount, and I have
> pointed out several issues such as
> - for users, the inode number may change silently. eg. copy-up.
> - hardlinks may break by copy-up.
> - read(2) may get an obsoleted filedata (fstat(2) for metadata too).
> - fcntl(F_SETLK) may be broken by copy-up.
> - unnecessary copy-up may happen, for example mmap(MAP_PRIVATE) after
>   open(O_RDWR).
> - Later I noticed one more thing. /proc/PID/{fd/,exe} may not work
>   correctly for overlayfs ...
> - etc...
> They are called "unPOSIXy behavior", and unforunately many of them are
> NOT seem to be addressed in recent patches either.
>
> Also I have posted
>         If the development of UnionMount is really stopped, then I'd ask people
>         to consider merging aufs as well as overlayfs.
> but I am not sure whether LKML people are still waiting for UnionMount
> and rejecting aufs.
>

Okajima san /o\,

thanks for the short summary of history, quick overview of AUFS
features and OverlayFS design.
I can't say much about AUFS, I just simply used it for so long.

But it looks like you agree with me that something should happen in
case of Union Filesystem's.
Anyway, as said I would like to see an upstream solution in the near future.
If this will be AUFS, I am OK with that decision.

Regards,
- Sedat -

> J. R. Okajima
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