linux-kernel - Re: [RFC PATCH] Show data flow for file copyup in unions

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Message-ID: <20100318175543.GA30924@shell>
Date:	Thu, 18 Mar 2010 13:55:43 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	Jeff Layton <jlayton@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Show data flow for file copyup in unions

On Thu, Mar 18, 2010 at 05:10:57PM +0900, J. R. Okajima wrote:
> 
> Valerie Aurora:
> > I think what people will expect is that we copy up in that case.  I
> > can think of ways this can go wrong, but perhaps that should be an
> > explicit requirement on the top-layer file system, that it can handle
> > create/unlink() in a directory without write permission.
> 
> I am not sure such requirement is the right way.
> How about delegating open() to keventd or some other workqueue which
> will succeed to create files under a directory without write permission?
> Of course, we should handle some error cases after creating a file.

Hm, I don't understand how handing it off to another thread would
help.  The thing I am worried about is some internal assumption in the
file system that a directory without write permission can't be
changed.  Totally manufactured example:

somefs_create()
{
	BUG_ON(IS_RDONLY(dir->d_inode);
[...]
}

-VAL
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