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Date: Sat, 12 Aug 2017 09:34:26 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax,
        dma-to-storage, and swap
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To: Andy Lutomirski <luto@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>, Christoph Hellwig <hch@lst.de>, "Darrick J. Wong" <darrick.wong@oracle.com>, Jan Kara <jack@suse.cz>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, Dave Chinner <david@fromorbit.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, linux-xfs@vger.kernel.org, Jeff Moyer <jmoyer@redhat.com>, Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Ross Zwisler <ross.zwisler@linux.intel.com>, Linux API <linux-api@vger.kernel.org>

On Fri, Aug 11, 2017 at 08:57:18PM -0700, Andy Lutomirski wrote:
> One thing that makes me quite nervous about S_IOMAP_IMMUTABLE is the
> degree to which things go badly if one program relies on it while
> another program clears the flag: you risk corrupting unrelated
> filesystem metadata.  I think a userspace interface to pin the extent
> mapping of a file really wants a way to reliably keep it pinned (or to
> reliably zap the userspace application if it gets unpinned).

The nice thing is that no application can rely on it anyway..