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Date: Tue, 7 Feb 2017 11:49:33 -0800
From: Christoph Hellwig <hch@infradead.org>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Christoph Hellwig <hch@infradead.org>,
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Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount
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On Tue, Feb 07, 2017 at 11:02:03AM -0800, James Bottomley wrote:
> >   Another option would be to require something like a project as used 
> > for project quotas as the root.  This would also be conveniant as it 
> > could storge the used remapping tables.
> 
> So this would be like the current project quota except set on a
> subtree?  I could see it being done that way but I don't see what
> advantage it has over using flags in the subtree itself (the mapping is
> known based on the mount namespace, so there's really only a single bit
> of information to store).

projects (which are the underling concept for project quotas) are
per-subtree in practice - the flag is set on an inode and then
all directories and files underneath inherit the project ID,
hardlinking outside a project is prohinited.