From: Andy Lutomirski <luto@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Linux API <linux-api@vger.kernel.org>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Dave Chinner <david@fromorbit.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-xfs@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andy Lutomirski <luto@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap
Date: Fri, 11 Aug 2017 20:57:18 -0700 [thread overview]
Message-ID: <CALCETrVvMbaxobdydtsdQWHyP1VhL1fpq1qS4M3=SmR1y4x5kw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4jrZ5a+zmAehZDxfP=+6BNCFAXOFWro2L7ruLkk+cY7OQ@mail.gmail.com>
On Fri, Aug 11, 2017 at 3:26 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Fri, Aug 11, 2017 at 3:44 AM, Christoph Hellwig <hch@lst.de> wrote:
>> Please explain how this interface allows for any sort of safe userspace
>> DMA.
>
> So this is where I continue to see S_IOMAP_IMMUTABLE being able to
> support applications that MAP_SYNC does not. Dave mentioned userspace
> pNFS4 servers, but there's also Samba and other protocols that want to
> negotiate a direct path to pmem outside the kernel. Xen support has
> thus far not been able to follow in the footsteps of KVM enabling due
> to a dependence on static M2P tables that assume a static
> guest-physical to host-physical relationship [1]. Immutable files
> would allow Xen to follow the same "mmap a file" semantic as KVM.
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).
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WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: 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>,
Andy Lutomirski <luto@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap
Date: Fri, 11 Aug 2017 20:57:18 -0700 [thread overview]
Message-ID: <CALCETrVvMbaxobdydtsdQWHyP1VhL1fpq1qS4M3=SmR1y4x5kw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4jrZ5a+zmAehZDxfP=+6BNCFAXOFWro2L7ruLkk+cY7OQ@mail.gmail.com>
On Fri, Aug 11, 2017 at 3:26 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Fri, Aug 11, 2017 at 3:44 AM, Christoph Hellwig <hch@lst.de> wrote:
>> Please explain how this interface allows for any sort of safe userspace
>> DMA.
>
> So this is where I continue to see S_IOMAP_IMMUTABLE being able to
> support applications that MAP_SYNC does not. Dave mentioned userspace
> pNFS4 servers, but there's also Samba and other protocols that want to
> negotiate a direct path to pmem outside the kernel. Xen support has
> thus far not been able to follow in the footsteps of KVM enabling due
> to a dependence on static M2P tables that assume a static
> guest-physical to host-physical relationship [1]. Immutable files
> would allow Xen to follow the same "mmap a file" semantic as KVM.
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).
next prev parent reply other threads:[~2017-08-12 3:55 UTC|newest]
Thread overview: 108+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-04 2:28 [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 2:28 ` [PATCH v2 1/5] fs, xfs: introduce S_IOMAP_IMMUTABLE Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 20:00 ` Darrick J. Wong
2017-08-04 20:00 ` Darrick J. Wong
2017-08-04 20:31 ` Dan Williams
2017-08-04 20:31 ` Dan Williams
2017-08-05 9:47 ` Christoph Hellwig
2017-08-05 9:47 ` Christoph Hellwig
2017-08-07 0:25 ` Dave Chinner
2017-08-07 0:25 ` Dave Chinner
2017-08-11 10:34 ` Christoph Hellwig
2017-08-11 10:34 ` Christoph Hellwig
2017-08-04 2:28 ` [PATCH v2 2/5] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 19:46 ` Darrick J. Wong
2017-08-04 19:46 ` Darrick J. Wong
2017-08-04 19:52 ` Dan Williams
2017-08-04 19:52 ` Dan Williams
2017-08-04 23:31 ` Dave Chinner
2017-08-04 23:31 ` Dave Chinner
2017-08-04 23:43 ` Dan Williams
2017-08-04 23:43 ` Dan Williams
2017-08-05 0:04 ` Dave Chinner
2017-08-05 0:04 ` Dave Chinner
2017-08-04 2:28 ` [PATCH v2 3/5] fs, xfs: introduce FALLOC_FL_UNSEAL_BLOCK_MAP Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 20:04 ` Darrick J. Wong
2017-08-04 20:04 ` Darrick J. Wong
2017-08-04 20:36 ` Dan Williams
2017-08-04 20:36 ` Dan Williams
2017-08-04 2:28 ` [PATCH v2 4/5] xfs: introduce XFS_DIFLAG2_IOMAP_IMMUTABLE Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 20:33 ` Darrick J. Wong
2017-08-04 20:33 ` Darrick J. Wong
2017-08-04 20:45 ` Dan Williams
2017-08-04 20:45 ` Dan Williams
2017-08-04 23:46 ` Dave Chinner
2017-08-04 23:46 ` Dave Chinner
2017-08-04 23:57 ` Darrick J. Wong
2017-08-04 23:57 ` Darrick J. Wong
2017-08-04 2:28 ` [PATCH v2 5/5] xfs: toggle XFS_DIFLAG2_IOMAP_IMMUTABLE in response to fallocate Dan Williams
2017-08-04 2:28 ` Dan Williams
2017-08-04 20:14 ` Darrick J. Wong
2017-08-04 20:14 ` Darrick J. Wong
2017-08-04 20:47 ` Dan Williams
2017-08-04 20:47 ` Dan Williams
2017-08-04 20:53 ` Darrick J. Wong
2017-08-04 20:53 ` Darrick J. Wong
2017-08-04 20:55 ` Dan Williams
2017-08-04 20:55 ` Dan Williams
2017-08-04 2:38 ` [PATCH v2 0/5] fs, xfs: block map immutable files for dax, dma-to-storage, and swap Dan Williams
2017-08-04 2:38 ` Dan Williams
2017-08-04 2:38 ` Dan Williams
2017-08-05 9:50 ` Christoph Hellwig
2017-08-05 9:50 ` Christoph Hellwig
2017-08-05 9:50 ` Christoph Hellwig
2017-08-06 18:51 ` Dan Williams
2017-08-06 18:51 ` Dan Williams
2017-08-06 18:51 ` Dan Williams
2017-08-11 10:44 ` Christoph Hellwig
2017-08-11 10:44 ` Christoph Hellwig
2017-08-11 10:44 ` Christoph Hellwig
2017-08-11 22:26 ` Dan Williams
2017-08-11 22:26 ` Dan Williams
2017-08-11 22:26 ` Dan Williams
2017-08-12 3:57 ` Andy Lutomirski [this message]
2017-08-12 3:57 ` Andy Lutomirski
2017-08-12 4:44 ` Dan Williams
2017-08-12 4:44 ` Dan Williams
2017-08-12 4:44 ` Dan Williams
2017-08-12 7:34 ` Christoph Hellwig
2017-08-12 7:34 ` Christoph Hellwig
2017-08-12 7:34 ` Christoph Hellwig
2017-08-12 7:33 ` Christoph Hellwig
2017-08-12 7:33 ` Christoph Hellwig
2017-08-12 7:33 ` Christoph Hellwig
2017-08-12 19:19 ` Dan Williams
2017-08-12 19:19 ` Dan Williams
2017-08-12 19:19 ` Dan Williams
2017-08-13 9:24 ` Christoph Hellwig
2017-08-13 9:24 ` Christoph Hellwig
2017-08-13 20:31 ` Dan Williams
2017-08-13 20:31 ` Dan Williams
2017-08-13 20:31 ` Dan Williams
2017-08-14 12:40 ` Jan Kara
2017-08-14 12:40 ` Jan Kara
2017-08-14 12:40 ` Jan Kara
2017-08-14 16:14 ` Dan Williams
2017-08-14 16:14 ` Dan Williams
2017-08-15 8:37 ` Jan Kara
2017-08-15 8:37 ` Jan Kara
2017-08-15 8:37 ` Jan Kara
2017-08-15 23:50 ` Dan Williams
2017-08-15 23:50 ` Dan Williams
2017-08-16 13:57 ` Jan Kara
2017-08-16 13:57 ` Jan Kara
2017-08-16 13:57 ` Jan Kara
2017-08-21 9:16 ` Peter Zijlstra
2017-08-21 9:16 ` Peter Zijlstra
2017-08-21 9:16 ` Peter Zijlstra
2017-08-14 21:46 ` Darrick J. Wong
2017-08-14 21:46 ` Darrick J. Wong
2017-08-14 21:46 ` Darrick J. Wong
2017-08-13 23:46 ` Dave Chinner
2017-08-13 23:46 ` Dave Chinner
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