[PATCH v5 0/2] dax, dm: stop requiring dax for device-mapper

[PATCH v5 0/2] dax, dm: stop requiring dax for device-mapper

[Dan Williams]

Changes since v4:
* redo a botched send of v3
* rebase on 4.14-rc1
* rewrite the changelog of patch2 to drop broken references to the
  "built-in portion of device-mapper" (Mike)

---

Bart points out that the DAX core is unconditionally enabled if
device-mapper is enabled. Add some config machinery and stub routines to
allow device-mapper to build and run with CONFIG_DAX=n.

---

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 v5 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 conditionally 'select DAX'
only 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 4a438b8abe27..5d4821c91a76 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -298,6 +298,7 @@ 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 v5 2/2] dm: allow device-mapper to operate without dax support

[Dan Williams]

Change device-mapper's 'select DAX' dependency to be dependent on the
presence of at least one DAX_DRIVER. This allows device-mapper to be
built without bringing the DAX core along which is especially wasteful
when there are no DAX drivers, like BLK_DEV_PMEM, configured.

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..baeea31dc858 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -200,7 +200,7 @@ config BLK_DEV_DM_BUILTIN
 config BLK_DEV_DM
 	tristate "Device mapper support"
 	select BLK_DEV_DM_BUILTIN
-	select DAX
+	select DAX if DAX_DRIVER
 	---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 d5f8eff7c11d..df4b6f0489aa 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)
 {
@@ -184,6 +185,11 @@ static size_t linear_dax_copy_from_iter(struct dm_target *ti, pgoff_t pgoff,
 	return dax_copy_from_iter(dax_dev, pgoff, addr, bytes, i);
 }
 
+#else
+#define linear_dax_direct_access NULL
+#define linear_dax_copy_from_iter NULL
+#endif
+
 static struct target_type linear_target = {
 	.name   = "linear",
 	.version = {1, 4, 0},
diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index b5e892149c54..8cb98ee2c9db 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)
 {
@@ -351,6 +352,11 @@ static size_t stripe_dax_copy_from_iter(struct dm_target *ti, pgoff_t pgoff,
 	return dax_copy_from_iter(dax_dev, pgoff, addr, bytes, i);
 }
 
+#else
+#define stripe_dax_direct_access NULL
+#define stripe_dax_copy_from_iter NULL
+#endif
+
 /*
  * Stripe status:
  *
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 6e54145969c5..e364c584a676 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1685,7 +1685,7 @@ 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;
 
@@ -1751,9 +1751,11 @@ 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 122197124b9d..898403da0458 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -25,16 +25,39 @@ 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);
@@ -79,18 +102,13 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 
 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);
 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, 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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Re: [PATCH v5 1/2] dax: introduce CONFIG_DAX_DRIVER

[Michael Ellerman]

Dan Williams <dan.j.williams@intel.com> writes:

> 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 conditionally 'select DAX'
> only 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


I would have thought you'd want to replace the select of DAX with
a select of DAX_DRIVER?

With the driver selecting both there's no need for the core to select
DAX, because all the DAX drivers have done it already.

cheers
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Re: [PATCH v5 1/2] dax: introduce CONFIG_DAX_DRIVER

[Dan Williams]

On Thu, Sep 28, 2017 at 11:11 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Dan Williams <dan.j.williams@intel.com> writes:
>
>> 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 conditionally 'select DAX'
>> only 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
>
>
> I would have thought you'd want to replace the select of DAX with
> a select of DAX_DRIVER?

Me too ;-)

> With the driver selecting both there's no need for the core to select
> DAX, because all the DAX drivers have done it already.

Thanks, yes, I'll fix that up.
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