linux-kernel - Re: [PATCH 0/3] iopmem : A block device for PCIe memory

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Date:   Thu, 27 Oct 2016 13:22:49 +0300
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>
Cc:     jgunthorpe@...idianresearch.com, sbates@...thin.com,
        "Raj, Ashok" <ashok.raj@...el.com>, haggaie@...lanox.com,
        linux-rdma@...r.kernel.org,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>,
        Jonathan Corbet <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        jim.macdonald@...rspin.com, Stephen Bates <sbates@...thlin.com>,
        linux-block@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        Jens Axboe <axboe@...com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 0/3] iopmem : A block device for PCIe memory


>> You do realise that local filesystems can silently change the
>> location of file data at any point in time, so there is no such
>> thing as a "stable mapping" of file data to block device addresses
>> in userspace?
>>
>> If you want remote access to the blocks owned and controlled by a
>> filesystem, then you need to use a filesystem with a remote locking
>> mechanism to allow co-ordinated, coherent access to the data in
>> those blocks. Anything else is just asking for ongoing, unfixable
>> filesystem corruption or data leakage problems (i.e.  security
>> issues).
>
> And at least for XFS we have such a mechanism :)  E.g. I have a
> prototype of a pNFS layout that uses XFS+DAX to allow clients to do
> RDMA directly to XFS files, with the same locking mechanism we use
> for the current block and scsi layout in xfs_pnfs.c.

Christoph, did you manage to leap to the future and solve the
RDMA persistency hole? :)

e.g. what happens with O_DSYNC in this model? Or you did
a message exchange for commits?