[PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Dan Williams]

Changes since v2 [1]:
* rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
  sure dm_dax_flush() is called if device supports it" (kbuild robot)
* fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
  (kbuild robot)

[1]: https://www.spinics.net/lists/kernel/msg2570522.html

---

Bart points out that the DAX core is unconditionally enabled if
device-mapper is enabled. Add some config machinery and some
stub-static-inline routines to allow dax infrastructure to be deleted
from device-mapper at compile time.

Since this depends on commit 273752c9ff03 that's already in -next, this
should go through the device-mapper tree.
---

Dan Williams (2):
      dax: introduce CONFIG_DAX_DRIVER
      dm: allow device-mapper to operate without dax support


 arch/powerpc/platforms/Kconfig |    1 +
 drivers/block/Kconfig          |    1 +
 drivers/dax/Kconfig            |    4 +++-
 drivers/md/Kconfig             |    2 +-
 drivers/md/dm-linear.c         |    6 ++++++
 drivers/md/dm-stripe.c         |    6 ++++++
 drivers/md/dm.c                |   10 ++++++----
 drivers/nvdimm/Kconfig         |    1 +
 drivers/s390/block/Kconfig     |    1 +
 include/linux/dax.h            |   30 ++++++++++++++++++++++++------
 10 files changed, 50 insertions(+), 12 deletions(-)
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[PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Dan Williams]

Changes since v2 [1]:
* rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
  sure dm_dax_flush() is called if device supports it" (kbuild robot)
* fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
  (kbuild robot)

[1]: https://www.spinics.net/lists/kernel/msg2570522.html

---

Bart points out that the DAX core is unconditionally enabled if
device-mapper is enabled. Add some config machinery and some
stub-static-inline routines to allow dax infrastructure to be deleted
from device-mapper at compile time.

Since this depends on commit 273752c9ff03 that's already in -next, this
should go through the device-mapper tree.
---

Dan Williams (2):
      dax: introduce CONFIG_DAX_DRIVER
      dm: allow device-mapper to operate without dax support


 arch/powerpc/platforms/Kconfig |    1 +
 drivers/block/Kconfig          |    1 +
 drivers/dax/Kconfig            |    4 +++-
 drivers/md/Kconfig             |    2 +-
 drivers/md/dm-linear.c         |    6 ++++++
 drivers/md/dm-stripe.c         |    6 ++++++
 drivers/md/dm.c                |   10 ++++++----
 drivers/nvdimm/Kconfig         |    1 +
 drivers/s390/block/Kconfig     |    1 +
 include/linux/dax.h            |   30 ++++++++++++++++++++++++------
 10 files changed, 50 insertions(+), 12 deletions(-)

[PATCH v3 1/2] dax: introduce CONFIG_DAX_DRIVER

[Dan Williams]

In support of allowing device-mapper to compile out idle/dead code when
there are no dax providers in the system, introduce the DAX_DRIVER
symbol. This is selected by all leaf drivers that device-mapper might be
layered on top. This allows device-mapper to 'select DAX', i.e. upgrade
it from DAX=m to DAX=y, when a provider is present.

Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/powerpc/platforms/Kconfig |    1 +
 drivers/block/Kconfig          |    1 +
 drivers/dax/Kconfig            |    4 +++-
 drivers/nvdimm/Kconfig         |    1 +
 drivers/s390/block/Kconfig     |    1 +
 5 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index 4fd64d3f5c44..4561340c1f92 100644
--- a/arch/powerpc/platforms/Kconfig
+++ b/arch/powerpc/platforms/Kconfig
@@ -296,6 +296,7 @@ config AXON_RAM
 	tristate "Axon DDR2 memory device driver"
 	depends on PPC_IBM_CELL_BLADE && BLOCK
 	select DAX
+	select DAX_DRIVER
 	default m
 	help
 	  It registers one block device per Axon's DDR2 memory bank found
diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 8ddc98279c8f..e1b6f4d2a716 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -324,6 +324,7 @@ config BLK_DEV_SX8
 config BLK_DEV_RAM
 	tristate "RAM block device support"
 	select DAX if BLK_DEV_RAM_DAX
+	select DAX_DRIVER if BLK_DEV_RAM_DAX
 	---help---
 	  Saying Y here will allow you to use a portion of your RAM memory as
 	  a block device, so that you can make file systems on it, read and
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index b79aa8f7a497..9bf940eb9c06 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,3 +1,6 @@
+config DAX_DRIVER
+	bool
+
 menuconfig DAX
 	tristate "DAX: direct access to differentiated memory"
 	select SRCU
@@ -16,7 +19,6 @@ config DEV_DAX
 	  baseline memory pool.  Mappings of a /dev/daxX.Y device impose
 	  restrictions that make the mapping behavior deterministic.
 
-
 config DEV_DAX_PMEM
 	tristate "PMEM DAX: direct access to persistent memory"
 	depends on LIBNVDIMM && NVDIMM_DAX && DEV_DAX
diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
index 5bdd499b5f4f..afe4018d76cf 100644
--- a/drivers/nvdimm/Kconfig
+++ b/drivers/nvdimm/Kconfig
@@ -21,6 +21,7 @@ config BLK_DEV_PMEM
 	tristate "PMEM: Persistent memory block device support"
 	default LIBNVDIMM
 	select DAX
+	select DAX_DRIVER
 	select ND_BTT if BTT
 	select ND_PFN if NVDIMM_PFN
 	help
diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig
index 31f014b57bfc..3f563f2f33d6 100644
--- a/drivers/s390/block/Kconfig
+++ b/drivers/s390/block/Kconfig
@@ -15,6 +15,7 @@ config BLK_DEV_XPRAM
 config DCSSBLK
 	def_tristate m
 	select DAX
+	select DAX_DRIVER
 	prompt "DCSSBLK support"
 	depends on S390 && BLOCK
 	help

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[PATCH v3 1/2] dax: introduce CONFIG_DAX_DRIVER

[Dan Williams]

In support of allowing device-mapper to compile out idle/dead code when
there are no dax providers in the system, introduce the DAX_DRIVER
symbol. This is selected by all leaf drivers that device-mapper might be
layered on top. This allows device-mapper to 'select DAX', i.e. upgrade
it from DAX=m to DAX=y, when a provider is present.

Cc: Paul Mackerras <paulus-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>
Cc: Michael Ellerman <mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org>
Cc: Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>
Cc: Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>
Cc: Gerald Schaefer <gerald.schaefer-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>
Cc: Benjamin Herrenschmidt <benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
Cc: Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org>
Signed-off-by: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 arch/powerpc/platforms/Kconfig |    1 +
 drivers/block/Kconfig          |    1 +
 drivers/dax/Kconfig            |    4 +++-
 drivers/nvdimm/Kconfig         |    1 +
 drivers/s390/block/Kconfig     |    1 +
 5 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index 4fd64d3f5c44..4561340c1f92 100644
--- a/arch/powerpc/platforms/Kconfig
+++ b/arch/powerpc/platforms/Kconfig
@@ -296,6 +296,7 @@ config AXON_RAM
 	tristate "Axon DDR2 memory device driver"
 	depends on PPC_IBM_CELL_BLADE && BLOCK
 	select DAX
+	select DAX_DRIVER
 	default m
 	help
 	  It registers one block device per Axon's DDR2 memory bank found
diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 8ddc98279c8f..e1b6f4d2a716 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -324,6 +324,7 @@ config BLK_DEV_SX8
 config BLK_DEV_RAM
 	tristate "RAM block device support"
 	select DAX if BLK_DEV_RAM_DAX
+	select DAX_DRIVER if BLK_DEV_RAM_DAX
 	---help---
 	  Saying Y here will allow you to use a portion of your RAM memory as
 	  a block device, so that you can make file systems on it, read and
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index b79aa8f7a497..9bf940eb9c06 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,3 +1,6 @@
+config DAX_DRIVER
+	bool
+
 menuconfig DAX
 	tristate "DAX: direct access to differentiated memory"
 	select SRCU
@@ -16,7 +19,6 @@ config DEV_DAX
 	  baseline memory pool.  Mappings of a /dev/daxX.Y device impose
 	  restrictions that make the mapping behavior deterministic.
 
-
 config DEV_DAX_PMEM
 	tristate "PMEM DAX: direct access to persistent memory"
 	depends on LIBNVDIMM && NVDIMM_DAX && DEV_DAX
diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
index 5bdd499b5f4f..afe4018d76cf 100644
--- a/drivers/nvdimm/Kconfig
+++ b/drivers/nvdimm/Kconfig
@@ -21,6 +21,7 @@ config BLK_DEV_PMEM
 	tristate "PMEM: Persistent memory block device support"
 	default LIBNVDIMM
 	select DAX
+	select DAX_DRIVER
 	select ND_BTT if BTT
 	select ND_PFN if NVDIMM_PFN
 	help
diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig
index 31f014b57bfc..3f563f2f33d6 100644
--- a/drivers/s390/block/Kconfig
+++ b/drivers/s390/block/Kconfig
@@ -15,6 +15,7 @@ config BLK_DEV_XPRAM
 config DCSSBLK
 	def_tristate m
 	select DAX
+	select DAX_DRIVER
 	prompt "DCSSBLK support"
 	depends on S390 && BLOCK
 	help

[PATCH v3 1/2] dax: introduce CONFIG_DAX_DRIVER

[Dan Williams]

In support of allowing device-mapper to compile out idle/dead code when
there are no dax providers in the system, introduce the DAX_DRIVER
symbol. This is selected by all leaf drivers that device-mapper might be
layered on top. This allows device-mapper to 'select DAX', i.e. upgrade
it from DAX=m to DAX=y, when a provider is present.

Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/powerpc/platforms/Kconfig |    1 +
 drivers/block/Kconfig          |    1 +
 drivers/dax/Kconfig            |    4 +++-
 drivers/nvdimm/Kconfig         |    1 +
 drivers/s390/block/Kconfig     |    1 +
 5 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index 4fd64d3f5c44..4561340c1f92 100644
--- a/arch/powerpc/platforms/Kconfig
+++ b/arch/powerpc/platforms/Kconfig
@@ -296,6 +296,7 @@ config AXON_RAM
 	tristate "Axon DDR2 memory device driver"
 	depends on PPC_IBM_CELL_BLADE && BLOCK
 	select DAX
+	select DAX_DRIVER
 	default m
 	help
 	  It registers one block device per Axon's DDR2 memory bank found
diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 8ddc98279c8f..e1b6f4d2a716 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -324,6 +324,7 @@ config BLK_DEV_SX8
 config BLK_DEV_RAM
 	tristate "RAM block device support"
 	select DAX if BLK_DEV_RAM_DAX
+	select DAX_DRIVER if BLK_DEV_RAM_DAX
 	---help---
 	  Saying Y here will allow you to use a portion of your RAM memory as
 	  a block device, so that you can make file systems on it, read and
diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index b79aa8f7a497..9bf940eb9c06 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -1,3 +1,6 @@
+config DAX_DRIVER
+	bool
+
 menuconfig DAX
 	tristate "DAX: direct access to differentiated memory"
 	select SRCU
@@ -16,7 +19,6 @@ config DEV_DAX
 	  baseline memory pool.  Mappings of a /dev/daxX.Y device impose
 	  restrictions that make the mapping behavior deterministic.
 
-
 config DEV_DAX_PMEM
 	tristate "PMEM DAX: direct access to persistent memory"
 	depends on LIBNVDIMM && NVDIMM_DAX && DEV_DAX
diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
index 5bdd499b5f4f..afe4018d76cf 100644
--- a/drivers/nvdimm/Kconfig
+++ b/drivers/nvdimm/Kconfig
@@ -21,6 +21,7 @@ config BLK_DEV_PMEM
 	tristate "PMEM: Persistent memory block device support"
 	default LIBNVDIMM
 	select DAX
+	select DAX_DRIVER
 	select ND_BTT if BTT
 	select ND_PFN if NVDIMM_PFN
 	help
diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig
index 31f014b57bfc..3f563f2f33d6 100644
--- a/drivers/s390/block/Kconfig
+++ b/drivers/s390/block/Kconfig
@@ -15,6 +15,7 @@ config BLK_DEV_XPRAM
 config DCSSBLK
 	def_tristate m
 	select DAX
+	select DAX_DRIVER
 	prompt "DCSSBLK support"
 	depends on S390 && BLOCK
 	help

[PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

Rather than have device-mapper directly 'select DAX', let the fact that
BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
support. We arrange for all the dax core routines to compile to nops
when CONFIG_DAX=n. With that in place we can simply handle the
alloc_dax() error as expected and ifdef out the other device-mapper-dax
support code.

Now, if dax is provided by a leaf driver that driver may only arrange to
compile the dax core as a module. Since device-mapper dax support is
consumed by the always-built-in portion of the device-mapper
implementation we need to upgrade from DAX=m to DAX=y.

Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/md/Kconfig     |    2 +-
 drivers/md/dm-linear.c |    6 ++++++
 drivers/md/dm-stripe.c |    6 ++++++
 drivers/md/dm.c        |   10 ++++++----
 include/linux/dax.h    |   30 ++++++++++++++++++++++++------
 5 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 4a249ee86364..8ebf09e99006 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -195,12 +195,12 @@ config MD_CLUSTER
 source "drivers/md/bcache/Kconfig"
 
 config BLK_DEV_DM_BUILTIN
+	select DAX if DAX_DRIVER
 	bool
 
 config BLK_DEV_DM
 	tristate "Device mapper support"
 	select BLK_DEV_DM_BUILTIN
-	select DAX
 	---help---
 	  Device-mapper is a low level volume manager.  It works by allowing
 	  people to specify mappings for ranges of logical sectors.  Various
diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index 41971a090e34..8804e278e834 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -154,6 +154,7 @@ static int linear_iterate_devices(struct dm_target *ti,
 	return fn(ti, lc->dev, lc->start, ti->len, data);
 }
 
+#if IS_ENABLED(CONFIG_DAX)
 static long linear_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
 		long nr_pages, void **kaddr, pfn_t *pfn)
 {
@@ -197,6 +198,11 @@ static void linear_dax_flush(struct dm_target *ti, pgoff_t pgoff, void *addr,
 		return;
 	dax_flush(dax_dev, pgoff, addr, size);
 }
+#else
+#define linear_dax_direct_access NULL
+#define linear_dax_copy_from_iter NULL
+#define linear_dax_flush NULL
+#endif
 
 static struct target_type linear_target = {
 	.name   = "linear",
diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index a0375530b07f..eeb6c784dc4f 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -311,6 +311,7 @@ static int stripe_map(struct dm_target *ti, struct bio *bio)
 	return DM_MAPIO_REMAPPED;
 }
 
+#if IS_ENABLED(CONFIG_DAX)
 static long stripe_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
 		long nr_pages, void **kaddr, pfn_t *pfn)
 {
@@ -369,6 +370,11 @@ static void stripe_dax_flush(struct dm_target *ti, pgoff_t pgoff, void *addr,
 		return;
 	dax_flush(dax_dev, pgoff, addr, size);
 }
+#else
+#define stripe_dax_direct_access NULL
+#define stripe_dax_copy_from_iter NULL
+#define stripe_dax_flush NULL
+#endif
 
 /*
  * Stripe status:
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2edbcc2d7d3f..70fa48f4d3a3 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1713,7 +1713,7 @@ static void cleanup_mapped_device(struct mapped_device *md)
 static struct mapped_device *alloc_dev(int minor)
 {
 	int r, numa_node_id = dm_get_numa_node();
-	struct dax_device *dax_dev;
+	struct dax_device *dax_dev = NULL;
 	struct mapped_device *md;
 	void *old_md;
 
@@ -1779,9 +1779,11 @@ static struct mapped_device *alloc_dev(int minor)
 	md->disk->private_data = md;
 	sprintf(md->disk->disk_name, "dm-%d", minor);
 
-	dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
-	if (!dax_dev)
-		goto bad;
+	if (IS_ENABLED(CONFIG_DAX)) {
+		dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
+		if (!dax_dev)
+			goto bad;
+	}
 	md->dax_dev = dax_dev;
 
 	add_disk(md->disk);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index eb0bff6f1eab..59575b8e638e 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -27,16 +27,39 @@ extern struct attribute_group dax_attribute_group;
 
 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *dax_get_by_host(const char *host);
+struct dax_device *alloc_dax(void *private, const char *host,
+		const struct dax_operations *ops);
 void put_dax(struct dax_device *dax_dev);
+void kill_dax(struct dax_device *dax_dev);
+void dax_write_cache(struct dax_device *dax_dev, bool wc);
+bool dax_write_cache_enabled(struct dax_device *dax_dev);
 #else
 static inline struct dax_device *dax_get_by_host(const char *host)
 {
 	return NULL;
 }
-
+static inline struct dax_device *alloc_dax(void *private, const char *host,
+		const struct dax_operations *ops)
+{
+	/*
+	 * Callers should check IS_ENABLED(CONFIG_DAX) to know if this
+	 * NULL is an error or expected.
+	 */
+	return NULL;
+}
 static inline void put_dax(struct dax_device *dax_dev)
 {
 }
+static inline void kill_dax(struct dax_device *dax_dev)
+{
+}
+static inline void dax_write_cache(struct dax_device *dax_dev, bool wc)
+{
+}
+static inline bool dax_write_cache_enabled(struct dax_device *dax_dev)
+{
+	return false;
+}
 #endif
 
 int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
@@ -75,10 +98,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
 
 int dax_read_lock(void);
 void dax_read_unlock(int id);
-struct dax_device *alloc_dax(void *private, const char *host,
-		const struct dax_operations *ops);
 bool dax_alive(struct dax_device *dax_dev);
-void kill_dax(struct dax_device *dax_dev);
 void *dax_get_private(struct dax_device *dax_dev);
 long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
 		void **kaddr, pfn_t *pfn);
@@ -86,8 +106,6 @@ size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 		size_t bytes, struct iov_iter *i);
 void dax_flush(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 		size_t size);
-void dax_write_cache(struct dax_device *dax_dev, bool wc);
-bool dax_write_cache_enabled(struct dax_device *dax_dev);
 
 ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops);

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[PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

Rather than have device-mapper directly 'select DAX', let the fact that
BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
support. We arrange for all the dax core routines to compile to nops
when CONFIG_DAX=n. With that in place we can simply handle the
alloc_dax() error as expected and ifdef out the other device-mapper-dax
support code.

Now, if dax is provided by a leaf driver that driver may only arrange to
compile the dax core as a module. Since device-mapper dax support is
consumed by the always-built-in portion of the device-mapper
implementation we need to upgrade from DAX=m to DAX=y.

Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/md/Kconfig     |    2 +-
 drivers/md/dm-linear.c |    6 ++++++
 drivers/md/dm-stripe.c |    6 ++++++
 drivers/md/dm.c        |   10 ++++++----
 include/linux/dax.h    |   30 ++++++++++++++++++++++++------
 5 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 4a249ee86364..8ebf09e99006 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -195,12 +195,12 @@ config MD_CLUSTER
 source "drivers/md/bcache/Kconfig"
 
 config BLK_DEV_DM_BUILTIN
+	select DAX if DAX_DRIVER
 	bool
 
 config BLK_DEV_DM
 	tristate "Device mapper support"
 	select BLK_DEV_DM_BUILTIN
-	select DAX
 	---help---
 	  Device-mapper is a low level volume manager.  It works by allowing
 	  people to specify mappings for ranges of logical sectors.  Various
diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index 41971a090e34..8804e278e834 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -154,6 +154,7 @@ static int linear_iterate_devices(struct dm_target *ti,
 	return fn(ti, lc->dev, lc->start, ti->len, data);
 }
 
+#if IS_ENABLED(CONFIG_DAX)
 static long linear_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
 		long nr_pages, void **kaddr, pfn_t *pfn)
 {
@@ -197,6 +198,11 @@ static void linear_dax_flush(struct dm_target *ti, pgoff_t pgoff, void *addr,
 		return;
 	dax_flush(dax_dev, pgoff, addr, size);
 }
+#else
+#define linear_dax_direct_access NULL
+#define linear_dax_copy_from_iter NULL
+#define linear_dax_flush NULL
+#endif
 
 static struct target_type linear_target = {
 	.name   = "linear",
diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index a0375530b07f..eeb6c784dc4f 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -311,6 +311,7 @@ static int stripe_map(struct dm_target *ti, struct bio *bio)
 	return DM_MAPIO_REMAPPED;
 }
 
+#if IS_ENABLED(CONFIG_DAX)
 static long stripe_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
 		long nr_pages, void **kaddr, pfn_t *pfn)
 {
@@ -369,6 +370,11 @@ static void stripe_dax_flush(struct dm_target *ti, pgoff_t pgoff, void *addr,
 		return;
 	dax_flush(dax_dev, pgoff, addr, size);
 }
+#else
+#define stripe_dax_direct_access NULL
+#define stripe_dax_copy_from_iter NULL
+#define stripe_dax_flush NULL
+#endif
 
 /*
  * Stripe status:
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2edbcc2d7d3f..70fa48f4d3a3 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1713,7 +1713,7 @@ static void cleanup_mapped_device(struct mapped_device *md)
 static struct mapped_device *alloc_dev(int minor)
 {
 	int r, numa_node_id = dm_get_numa_node();
-	struct dax_device *dax_dev;
+	struct dax_device *dax_dev = NULL;
 	struct mapped_device *md;
 	void *old_md;
 
@@ -1779,9 +1779,11 @@ static struct mapped_device *alloc_dev(int minor)
 	md->disk->private_data = md;
 	sprintf(md->disk->disk_name, "dm-%d", minor);
 
-	dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
-	if (!dax_dev)
-		goto bad;
+	if (IS_ENABLED(CONFIG_DAX)) {
+		dax_dev = alloc_dax(md, md->disk->disk_name, &dm_dax_ops);
+		if (!dax_dev)
+			goto bad;
+	}
 	md->dax_dev = dax_dev;
 
 	add_disk(md->disk);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index eb0bff6f1eab..59575b8e638e 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -27,16 +27,39 @@ extern struct attribute_group dax_attribute_group;
 
 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *dax_get_by_host(const char *host);
+struct dax_device *alloc_dax(void *private, const char *host,
+		const struct dax_operations *ops);
 void put_dax(struct dax_device *dax_dev);
+void kill_dax(struct dax_device *dax_dev);
+void dax_write_cache(struct dax_device *dax_dev, bool wc);
+bool dax_write_cache_enabled(struct dax_device *dax_dev);
 #else
 static inline struct dax_device *dax_get_by_host(const char *host)
 {
 	return NULL;
 }
-
+static inline struct dax_device *alloc_dax(void *private, const char *host,
+		const struct dax_operations *ops)
+{
+	/*
+	 * Callers should check IS_ENABLED(CONFIG_DAX) to know if this
+	 * NULL is an error or expected.
+	 */
+	return NULL;
+}
 static inline void put_dax(struct dax_device *dax_dev)
 {
 }
+static inline void kill_dax(struct dax_device *dax_dev)
+{
+}
+static inline void dax_write_cache(struct dax_device *dax_dev, bool wc)
+{
+}
+static inline bool dax_write_cache_enabled(struct dax_device *dax_dev)
+{
+	return false;
+}
 #endif
 
 int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
@@ -75,10 +98,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
 
 int dax_read_lock(void);
 void dax_read_unlock(int id);
-struct dax_device *alloc_dax(void *private, const char *host,
-		const struct dax_operations *ops);
 bool dax_alive(struct dax_device *dax_dev);
-void kill_dax(struct dax_device *dax_dev);
 void *dax_get_private(struct dax_device *dax_dev);
 long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
 		void **kaddr, pfn_t *pfn);
@@ -86,8 +106,6 @@ size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 		size_t bytes, struct iov_iter *i);
 void dax_flush(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 		size_t size);
-void dax_write_cache(struct dax_device *dax_dev, bool wc);
-bool dax_write_cache_enabled(struct dax_device *dax_dev);
 
 ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops);

Re: [PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Mike Snitzer]

On Wed, Aug 02 2017 at  1:58pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> Rather than have device-mapper directly 'select DAX', let the fact that
> BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
> support. We arrange for all the dax core routines to compile to nops
> when CONFIG_DAX=n. With that in place we can simply handle the
> alloc_dax() error as expected and ifdef out the other device-mapper-dax
> support code.
> 
> Now, if dax is provided by a leaf driver that driver may only arrange to
> compile the dax core as a module. Since device-mapper dax support is
> consumed by the always-built-in portion of the device-mapper
> implementation we need to upgrade from DAX=m to DAX=y.

I applied the patches and then got nervous once I dug in.. this last
paragraph makes little sense to me.  "the always-built-in portion of the
device-mapper implementation" is why: DM core can happily be compiled as
a module (dm-mod.ko).

And I'm not sure why you're referencing DAX related
drivers/md/dm-builtin.c, why are you attachd DM's DAX support to that?
I'm not seeing where that is actually happening.

I don't see why DM's support for DAX would need to force DAX to be
builtin rather than just a module.

Sorry I didn't get around to looking at this until now, but it seems you
went wrong along the way?  Or maybe I'm just missing something?

Mike
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Re: [PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Mike Snitzer]

On Wed, Aug 02 2017 at  1:58pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> Rather than have device-mapper directly 'select DAX', let the fact that
> BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
> support. We arrange for all the dax core routines to compile to nops
> when CONFIG_DAX=n. With that in place we can simply handle the
> alloc_dax() error as expected and ifdef out the other device-mapper-dax
> support code.
> 
> Now, if dax is provided by a leaf driver that driver may only arrange to
> compile the dax core as a module. Since device-mapper dax support is
> consumed by the always-built-in portion of the device-mapper
> implementation we need to upgrade from DAX=m to DAX=y.

I applied the patches and then got nervous once I dug in.. this last
paragraph makes little sense to me.  "the always-built-in portion of the
device-mapper implementation" is why: DM core can happily be compiled as
a module (dm-mod.ko).

And I'm not sure why you're referencing DAX related
drivers/md/dm-builtin.c, why are you attachd DM's DAX support to that?
I'm not seeing where that is actually happening.

I don't see why DM's support for DAX would need to force DAX to be
builtin rather than just a module.

Sorry I didn't get around to looking at this until now, but it seems you
went wrong along the way?  Or maybe I'm just missing something?

Mike

Re: [PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

On Mon, Sep 11, 2017 at 7:41 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Wed, Aug 02 2017 at  1:58pm -0400,
> Dan Williams <dan.j.williams@intel.com> wrote:
>
>> Rather than have device-mapper directly 'select DAX', let the fact that
>> BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
>> support. We arrange for all the dax core routines to compile to nops
>> when CONFIG_DAX=n. With that in place we can simply handle the
>> alloc_dax() error as expected and ifdef out the other device-mapper-dax
>> support code.
>>
>> Now, if dax is provided by a leaf driver that driver may only arrange to
>> compile the dax core as a module. Since device-mapper dax support is
>> consumed by the always-built-in portion of the device-mapper
>> implementation we need to upgrade from DAX=m to DAX=y.
>
> I applied the patches and then got nervous once I dug in.. this last
> paragraph makes little sense to me.  "the always-built-in portion of the
> device-mapper implementation" is why: DM core can happily be compiled as
> a module (dm-mod.ko).
>
> And I'm not sure why you're referencing DAX related
> drivers/md/dm-builtin.c, why are you attachd DM's DAX support to that?
> I'm not seeing where that is actually happening.
>
> I don't see why DM's support for DAX would need to force DAX to be
> builtin rather than just a module.
>
> Sorry I didn't get around to looking at this until now, but it seems you
> went wrong along the way?  Or maybe I'm just missing something?
>

No, my fault, I didn't track BLK_DEV_DM_BUILTIN correctly and we can
safely make DAX a module when CONFIG_BLK_DEV_DM=m. I'll fix that up,
thanks for the catch.
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Re: [PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

On Mon, Sep 11, 2017 at 7:41 AM, Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> On Wed, Aug 02 2017 at  1:58pm -0400,
> Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>
>> Rather than have device-mapper directly 'select DAX', let the fact that
>> BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
>> support. We arrange for all the dax core routines to compile to nops
>> when CONFIG_DAX=n. With that in place we can simply handle the
>> alloc_dax() error as expected and ifdef out the other device-mapper-dax
>> support code.
>>
>> Now, if dax is provided by a leaf driver that driver may only arrange to
>> compile the dax core as a module. Since device-mapper dax support is
>> consumed by the always-built-in portion of the device-mapper
>> implementation we need to upgrade from DAX=m to DAX=y.
>
> I applied the patches and then got nervous once I dug in.. this last
> paragraph makes little sense to me.  "the always-built-in portion of the
> device-mapper implementation" is why: DM core can happily be compiled as
> a module (dm-mod.ko).
>
> And I'm not sure why you're referencing DAX related
> drivers/md/dm-builtin.c, why are you attachd DM's DAX support to that?
> I'm not seeing where that is actually happening.
>
> I don't see why DM's support for DAX would need to force DAX to be
> builtin rather than just a module.
>
> Sorry I didn't get around to looking at this until now, but it seems you
> went wrong along the way?  Or maybe I'm just missing something?
>

No, my fault, I didn't track BLK_DEV_DM_BUILTIN correctly and we can
safely make DAX a module when CONFIG_BLK_DEV_DM=m. I'll fix that up,
thanks for the catch.

Re: [PATCH v3 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

On Mon, Sep 11, 2017 at 7:41 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Wed, Aug 02 2017 at  1:58pm -0400,
> Dan Williams <dan.j.williams@intel.com> wrote:
>
>> Rather than have device-mapper directly 'select DAX', let the fact that
>> BLK_DEV_PMEM selects dax act as a gate for the device-mapper dax
>> support. We arrange for all the dax core routines to compile to nops
>> when CONFIG_DAX=n. With that in place we can simply handle the
>> alloc_dax() error as expected and ifdef out the other device-mapper-dax
>> support code.
>>
>> Now, if dax is provided by a leaf driver that driver may only arrange to
>> compile the dax core as a module. Since device-mapper dax support is
>> consumed by the always-built-in portion of the device-mapper
>> implementation we need to upgrade from DAX=m to DAX=y.
>
> I applied the patches and then got nervous once I dug in.. this last
> paragraph makes little sense to me.  "the always-built-in portion of the
> device-mapper implementation" is why: DM core can happily be compiled as
> a module (dm-mod.ko).
>
> And I'm not sure why you're referencing DAX related
> drivers/md/dm-builtin.c, why are you attachd DM's DAX support to that?
> I'm not seeing where that is actually happening.
>
> I don't see why DM's support for DAX would need to force DAX to be
> builtin rather than just a module.
>
> Sorry I didn't get around to looking at this until now, but it seems you
> went wrong along the way?  Or maybe I'm just missing something?
>

No, my fault, I didn't track BLK_DEV_DM_BUILTIN correctly and we can
safely make DAX a module when CONFIG_BLK_DEV_DM=m. I'll fix that up,
thanks for the catch.

Re: [PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Mike Snitzer]

On Wed, Aug 02 2017 at  1:57pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> Changes since v2 [1]:
> * rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
>   sure dm_dax_flush() is called if device supports it" (kbuild robot)
> * fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
>   (kbuild robot)
> 
> [1]: https://www.spinics.net/lists/kernel/msg2570522.html
> 
> ---
> 
> Bart points out that the DAX core is unconditionally enabled if
> device-mapper is enabled. Add some config machinery and some
> stub-static-inline routines to allow dax infrastructure to be deleted
> from device-mapper at compile time.
> 
> Since this depends on commit 273752c9ff03 that's already in -next, this
> should go through the device-mapper tree.

Commit 273752c9ff03eb83856601b2a3458218bb949e46 is upstream as of
v4.13-rc3 -- so no real need to have this go via linux-dm.git

That said, I don't mind picking it up once we are satisfied with the
implementation.  I'll start reviewing shortly.

Mike
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Re: [PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Mike Snitzer]

On Wed, Aug 02 2017 at  1:57pm -0400,
Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

> Changes since v2 [1]:
> * rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
>   sure dm_dax_flush() is called if device supports it" (kbuild robot)
> * fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
>   (kbuild robot)
> 
> [1]: https://www.spinics.net/lists/kernel/msg2570522.html
> 
> ---
> 
> Bart points out that the DAX core is unconditionally enabled if
> device-mapper is enabled. Add some config machinery and some
> stub-static-inline routines to allow dax infrastructure to be deleted
> from device-mapper at compile time.
> 
> Since this depends on commit 273752c9ff03 that's already in -next, this
> should go through the device-mapper tree.

Commit 273752c9ff03eb83856601b2a3458218bb949e46 is upstream as of
v4.13-rc3 -- so no real need to have this go via linux-dm.git

That said, I don't mind picking it up once we are satisfied with the
implementation.  I'll start reviewing shortly.

Mike

Re: [PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Mike Snitzer]

On Wed, Aug 02 2017 at  1:57pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> Changes since v2 [1]:
> * rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
>   sure dm_dax_flush() is called if device supports it" (kbuild robot)
> * fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
>   (kbuild robot)
> 
> [1]: https://www.spinics.net/lists/kernel/msg2570522.html
> 
> ---
> 
> Bart points out that the DAX core is unconditionally enabled if
> device-mapper is enabled. Add some config machinery and some
> stub-static-inline routines to allow dax infrastructure to be deleted
> from device-mapper at compile time.
> 
> Since this depends on commit 273752c9ff03 that's already in -next, this
> should go through the device-mapper tree.

Commit 273752c9ff03eb83856601b2a3458218bb949e46 is upstream as of
v4.13-rc3 -- so no real need to have this go via linux-dm.git

That said, I don't mind picking it up once we are satisfied with the
implementation.  I'll start reviewing shortly.

Mike

Re: [PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Dan Williams]

On Wed, Aug 2, 2017 at 11:55 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Wed, Aug 02 2017 at  1:57pm -0400,
> Dan Williams <dan.j.williams@intel.com> wrote:
>
>> Changes since v2 [1]:
>> * rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
>>   sure dm_dax_flush() is called if device supports it" (kbuild robot)
>> * fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
>>   (kbuild robot)
>>
>> [1]: https://www.spinics.net/lists/kernel/msg2570522.html
>>
>> ---
>>
>> Bart points out that the DAX core is unconditionally enabled if
>> device-mapper is enabled. Add some config machinery and some
>> stub-static-inline routines to allow dax infrastructure to be deleted
>> from device-mapper at compile time.
>>
>> Since this depends on commit 273752c9ff03 that's already in -next, this
>> should go through the device-mapper tree.
>
> Commit 273752c9ff03eb83856601b2a3458218bb949e46 is upstream as of
> v4.13-rc3 -- so no real need to have this go via linux-dm.git
>
> That said, I don't mind picking it up once we are satisfied with the
> implementation.  I'll start reviewing shortly.

Hi Mike,

Friendly reminder about this cleanup...
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Re: [PATCH v3 0/2] dax, dm: stop requiring dax for device-mapper

[Dan Williams]

On Wed, Aug 2, 2017 at 11:55 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> On Wed, Aug 02 2017 at  1:57pm -0400,
> Dan Williams <dan.j.williams@intel.com> wrote:
>
>> Changes since v2 [1]:
>> * rebase on -next to integrate with commit 273752c9ff03 "dm, dax: Make
>>   sure dm_dax_flush() is called if device supports it" (kbuild robot)
>> * fix CONFIG_DAX dependencies to upgrade CONFIG_DAX=m to CONFIG_DAX=y
>>   (kbuild robot)
>>
>> [1]: https://www.spinics.net/lists/kernel/msg2570522.html
>>
>> ---
>>
>> Bart points out that the DAX core is unconditionally enabled if
>> device-mapper is enabled. Add some config machinery and some
>> stub-static-inline routines to allow dax infrastructure to be deleted
>> from device-mapper at compile time.
>>
>> Since this depends on commit 273752c9ff03 that's already in -next, this
>> should go through the device-mapper tree.
>
> Commit 273752c9ff03eb83856601b2a3458218bb949e46 is upstream as of
> v4.13-rc3 -- so no real need to have this go via linux-dm.git
>
> That said, I don't mind picking it up once we are satisfied with the
> implementation.  I'll start reviewing shortly.

Hi Mike,

Friendly reminder about this cleanup...