linux-kernel - [PATCH 0/2] Support DAX for device-mapper dm-linear devices

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Date:	Tue, 28 Jun 2016 13:37:14 -0600
From:	Toshi Kani <toshi.kani@....com>
To:	snitzer@...hat.com
Cc:	agk@...hat.com, dan.j.williams@...el.com,
	linux-nvdimm@...ts.01.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] Support DAX for device-mapper dm-linear devices

I noticed that dm-snap reloads DM table of target mapped-device, which
fails for dax-capable device after dax support is added.  Ideally,
adding dax support to dm-snap solves the issue, but it cannot be done
easily.  This patch-set allows dm-snap to work with dax-capable target
devices when bio-based operation is used.

dax operation is unsupported with dm-snap, such that:
 a) After snapshot is taken, mount with dax option to a target device
    or a snapshot device fails.  They can be mounted without dax.
 b) After snapshot is taken to a dax-mounted target device, any writes 
    to the target device fails (EIO).

b) can be protected by changing lvcreate to fail when snapshot is
requested to a dax-mounted target device. 

- Patch 1 solves an error when lvremove is made to a snapshot device.
- Patch 2 solves an error when lvcreate --snapshot is made to a dax-
  capable device.

---
Toshi Kani (2):
 1/2 dm: update table type check for dax
 2/2 dm snap: add fake origin_direct_access

---
 drivers/md/dm-ioctl.c | 11 ++++++++++-
 drivers/md/dm-snap.c  |  8 ++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)