linux-kernel - Re: [PATCH 0/6 v7] overlay filesystem

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Date:	Fri, 25 Mar 2011 00:24:26 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	"Hans-Peter Jansen" <hpj@...la.net>
Cc:	Xianghua Xiao <xiaoxianghua@...il.com>,
	Felix Fietkau <nbd@...nwrt.org>, linux-kernel@...r.kernel.org,
	neilb@...e.de
Subject: Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

(removed aufs-users ML since it is restricted to its members only)

"Hans-Peter Jansen":
> and aufs2: it's a minimalistic version of a layered filesystem, being=20
	:::

Thanks reminding us about aufs. :-)

As far as I know, overlayfs has some problems (minors?) similar to
UnionMount.
- 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).

And I noticed overlayfs adopts overriding credentials for copy-up.
Although I didn't read about credintials in detail yet, is it safe?
For example, during copy-up other thread in the same process may gain
the higher capabilities unexpectedly? Signal hander in the process too?

I just have read overlayfs once a long time ago, so I may be
misunderstanding.
But I have no objection to merge overlayfs into mainline.

Also I'd like to thank you Pete about mentioning the recent disaster in
Japan.

J. R. Okajima
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