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

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Date:	Fri, 15 Jul 2011 22:02:08 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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,
	hramrach@...trum.cz, jordipujolp@...il.com, ezk@....cs.sunysb.edu
Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion


Miklos Szeredi:
> st_nlink==1 for directories is widely accepted way of saying that the
> number of subdirectories is unknown.  Various filesystems already do
> this, and versions of GNU utils that I have come across accept it.

When the upperdir is tmpfs, the link count of the directories in it will
not be 1, won't it?


> > - If I remember correctly, Valerie Aurora has pointed out that
> >   open(O_RDONLY) + fchmod() will work correctly in UnionMount.
> >   It is true in overlayfs too?
>
> Neither union-mounts nor overlayfs can handle this case.

Oh, I meant "will work NOT correctly". Sorry.


> I hadn't thought about this case, so overlayfs would modify the lower
> filesystem in that case, which is a no-no.
>
> Following patch fixes this and return -EROFS for the above case.  I also
> updated the non-standard section in the docs.

Hmm, such changes to mnt_flags looks slightly rude to me. Do we have to
consider about these?
- there may exist files opened as RW on the lower.
- when overlayfs is unmounted, it should restore the original mnt_flags.
- (there may exist more...)

If overlayfs doesn't expect the lower mounted as RW, then it might be
better to reject it simply at mounting.


J. R. Okajima
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