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Date:      Thu, 1 Mar 2012 18:45:11 +0200
From:      Gleb Kurtsou <gleb.kurtsou@gmail.com>
To:        Christoph Hellwig <hch@infradead.org>
Cc:        Attilio Rao <attilio@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com>, Pawel Jakub Dawidek <pjd@FreeBSD.org>, arch@freebsd.org
Subject:   Re: Prefaulting for i/o buffers
Message-ID:  <20120301164511.GA1501@reks>
In-Reply-To: <20120301141010.GA7079@infradead.org>
References:  <20120203193719.GB3283@deviant.kiev.zoral.com.ua> <CAJ-FndABi21GfcCRTZizCPc_Mnxm1EY271BiXcYt9SD_zXFpXw@mail.gmail.com> <20120225151334.GH1344@garage.freebsd.pl> <CAJ-FndBBKHrpB1MNJTXx8gkFXR2d-O6k5-HJeOAyv2DznpN-QQ@mail.gmail.com> <20120225194630.GI1344@garage.freebsd.pl> <20120301111624.GB30991@reks> <20120301141010.GA7079@infradead.org>

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On (01/03/2012 09:10), Christoph Hellwig wrote:
> On Thu, Mar 01, 2012 at 01:16:24PM +0200, Gleb Kurtsou wrote:
> > Are you aware of a real "libraries for file systems" VFS example? It
> > sounds very interesting but I'm afraid it's going to look good only in
> > theory. E.g. locking at file system level (Darwin, Dragonfly BSD) looks
> > rather messy (IMHO) and more likely to be bug prone. On the other side
> > Linux has optional per file system rename lock making VOP_RENAME
> > implementation much easier, while ours is tremendously difficult to do
> > right.
> 
> All namespace locking in Linux is in the VFS, and it mandatory.  A
> filesystem wide lock is only used for cross-directory renames.
> 
> A more detailed description is here:
> 
> 	http://git.kernel.dk/?p=linux.git;a=blob;f=Documentation/filesystems/directory-locking
> 

My bad. I thought s_vfs_rename_mutex can be optional. Quite unfortunate
linux doesn't support concurrent cross-directory renames :)

Thanks,
Gleb.



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