linux-kernel - Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap

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Message-ID: <20170812073426.GB12679@lst.de>
Date:   Sat, 12 Aug 2017 09:34:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Dave Chinner <david@...morbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax,
        dma-to-storage, and swap

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..