linux-kernel - Re: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file

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Message-ID: <20090603063815.GE27563@wotan.suse.de>
Date:	Wed, 3 Jun 2009 08:38:15 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, Hugh Dickins <hugh@...itas.com>,
	Tejun Heo <tj@...nel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file

On Tue, Jun 02, 2009 at 03:56:02PM -0700, Eric W. Biederman wrote:
> Nick Piggin <npiggin@...e.de> writes:
> 
> >> In addition for a complete solution we need:
> >> - A reliable way the file structures that we need to revoke.
> >> - To wait for but not tamper with ongoing file creation and cleanup.
> >> - A guarantee that all with user space controlled duration are removed.
> >> 
> >> The file_hotplug_lock has a very unique implementation necessitated by
> >> the need to have no performance impact on existing code.  Classic locking
> >
> > Well, it isn't no performance impact. Function calls, branches, icache
> > and dcache...
> 
> Practically none.

OK that's different from none. There is obviously overhead.

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