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Re: a simple and scalable pNFS block layout server V2

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: a simple and scalable pNFS block layout server V2
From: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date: Thu, 22 Jan 2015 11:04:15 -0500
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, Jeff Layton <jlayton@xxxxxxxxxxxxxxx>, Linux NFS Mailing List <linux-nfs@xxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1421925006-24231-1-git-send-email-hch@xxxxxx>
References: <1421925006-24231-1-git-send-email-hch@xxxxxx>
Hi Christoph-

Very nice, and welcome, work.

On Jan 22, 2015, at 6:09 AM, Christoph Hellwig <hch@xxxxxx> wrote:

> This series adds support for the pNFS operations in NFS v4.1, as well
> as a block layout driver that can export block based filesystems that
> implement a few additional export operations.  Support for XFS is
> provided in this series, but other filesystems could be added easily.

I’m still not clear on what layout types are supported. Clearly
the block layout type is supported. But you mention XFS here. Does
that mean file layouts are also supported now? If so, can you
briefly describe the architecture and any current limitations?

Did I miss documentation for how administrators construct layouts?

> The core pNFS code of course owns its heritage to the existing Linux
> pNFS server prototype, but except for a few bits and pieces in the
> XDR path nothing is left from it.
> The design of this new pNFS server is fairly different from the old
> one - while the old one implemented very little semantics in nfsd
> and left almost everything to filesystems my implementation implements
> as much as possible in common nfsd code, then dispatches to a layout
> driver that still is part of nfsd and only then calls into the
> filesystem, thus keeping it free from intimate pNFS knowledge.
> This version of the code has been rebased to the locks-for-3.20
> tree which adds a new lock context structure to the inode.  For now
> we still (ab)use the lease list like in the last version.  Adding
> a pNFS-specific list would duplicate a lot of code without much
> benefit.  But during this research I came up with way to associate
> a nfs4_file with a struct file at open time which should allow
> to greatly simplify the pNFS and delegation code.  So stay tuned
> for some patches in this area!
> For now this also doesn't take errata 3901 for rfc 5661 into account
> yet and sticks to the verified errata.  The changes in 3901 seem
> useful in the longer run one verified and will be implemented
> eventually. Note that the only existing pNFS block client (Linux)
> would not benefit from the longer layout lifetimes anyway.
> More details are document in the individual patch descriptions and
> code comments.
> This code is also available from:
>       git://git.infradead.org/users/hch/pnfs.git pnfsd-for-3.20-2
> Changes since V1:
>       - rebased to the locks-for-3.20 tree
>       - fixed a memory leak in the nfsd4_encode_getdeviceinfo error path
>       - removed the always one lg_roc field
>       - added a nopnfs export option
>       - use a synchronous transaction in layoutget to simplify recovery
>       - various XFS fixes pointed out by Dave
>       - various documentation typo fixes
> --
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Chuck Lever

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