linux-kernel - Re: [PATCH 0/7] overlay filesystem: request for inclusion

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Date:	Fri, 17 Jun 2011 00:15:53 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Michal Suchanek <hramrach@...trum.cz>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Valerie Aurora <val@...consulting.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	NeilBrown <neilb@...e.de>, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, apw@...onical.com, nbd@...nwrt.org,
	jordipujolp@...il.com, ezk@....cs.sunysb.edu
Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion


Michal Suchanek:
> Probably swap the two above, you can't make a whiteout in presence of
> the directory, right?
> Anyway, you could just mark dirA as whiteout and remove any whiteouts
> contained in it asynchronously, and only jump through these hoops when
> trying to create a new entry in place of non-empty whiteout, or sync
> on emptying the old whiteout before making a new entry.

Unfortunately I cannot understand what you wrote.

First, the order of
> - create whiteout for dirA
> - rename dirA to .wh..wh.XXXXXXXX
is correct and I think it should be, in order to make a little help for
fsck/auchk.
And what is "non-empty whiteout" and "emptying the old whiteout"?
The whiteout is a size zero-ed and hardlinked regular file in aufs.


> Yes, it can only cause pollution with whiteouts unrelated to any files
> that ever existed which is not too much of an issue unless people want
> to add random stuff to the lower layer and see it in the union when
> they reconstruct it again.

??
Do you think that the .wh..wh.XXXXXXXX hides something on the lower
layer? If so, it is wrong. Such doubly whiteout hides nothing except
itself.


> It is only valid when in the upper layer of a union. However, so is
> whiteout, and so are files that were visible in the union but are not
> visible in the top layer if examined separately, outside of the union.

Do you mean that your special symlink has totally different file-type
from a symlink?
Anyway what I want to say is, what such symlink refers may differ
from what users originally expect. But I may misunderstand what you call
"fallthru symlink".


J. R. Okajima
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