linux-kernel - Re: [RFC PATCH 2/2] mm, fs: daxfile, an interface for byte-addressable updates to pmem

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Date:   Thu, 22 Jun 2017 00:09:58 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        akpm@...ux-foundation.org, Jan Kara <jack@...e.cz>,
        linux-nvdimm@...ts.01.org, linux-api@...r.kernel.org,
        Dave Chinner <david@...morbit.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jeff Moyer <jmoyer@...hat.com>, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@....de>, xfs <linux-xfs@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] mm, fs: daxfile, an interface for
 byte-addressable updates to pmem

On Tue, Jun 20, 2017 at 09:42:55AM -0600, Ross Zwisler wrote:
> On Mon, Jun 19, 2017 at 10:22:14PM -0700, Darrick J. Wong wrote:
> <>
> > Fourth, the VFS entry points for things like read, write, truncate,
> > utimes, fallocate, etc. all just bail out if S_IOMAP_FROZEN is set on a
> > file, so that the block map cannot be modified.  mmap is still allowed,
> > as we've discussed.  /Maybe/ we can allow fallocate to extend a file
> > with zeroed extents (it will be slow) as I've heard murmurs about
> > wanting to be able to extend a file, maybe not.
> 
> Read and write should still be allowed, right?

<shrug> I had thought the usage model was pretty slanted towards mmap,
but it's not a big deal to turn read/writes into glorified memcpy,
provided we reject the io request if it goes past EOF.

--D

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