linux-kernel - Re: [patch 3/5] VFS: pass open file to ->xattr()

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Date:	Fri, 21 Sep 2007 14:06:42 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	hch@...radead.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 3/5] VFS: pass open file to ->xattr()

On Fri, Sep 21, 2007 at 03:00:06PM +0200, Miklos Szeredi wrote:
> I don't think it's silly.  Read/write get passed the file descriptor,
> and it makes a lot of sense, if the filesystem has stateful opens.
> 
> Similarly for any fs operation that gets a file descriptor, it makes
> sense to pass the relevant open file down into the filesystem.

read/write fundamentally operate on file descriptors.  None of these
operations does, rather their normal forms get a path name and special
forms operate on a file descriptor to avoid lookup races.  Still the
underlying operation has nothing to do with the file descriptor at all.

> If you look carefully, the ftrunacate() already does this, becuse
> without that it's impossible to implement correct semantics in the
> filesystem in some cases.

ftruncate is a special case due to O_TRUNC.  But I have plans to solve
this whole issue more elegant than the current hack.

> For other operations it's not impossible, but it would mean more hacks
> in the filesystem itself (such as sillyrenaming) that are entirely
> unneeded if the file info is available.

It's not a problem at all for filesystem that implement normal unix
semantics.  If you want to shoer-horn strange semantics that barely
fit, you'll need some more hacks.
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