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Subject[PATCH v2] dm: allow device-mapper to operate without dax support
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Rather than 'select dax', let the fact that BLK_DEV_PMEM selects dax act
as a gate for the device-mapper dax support. Given that all the dax core
routines compile to nops when CONFIG_DAX=n, we can simply handle the
alloc_dax() error as expected and ifdef out the other dax support code.

Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/md/Kconfig | 1 -
drivers/md/dm-linear.c | 6 ++++++
drivers/md/dm-stripe.c | 6 ++++++
drivers/md/dm.c | 10 ++++++----
include/linux/dax.h | 19 +++++++++++++++----
5 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 4a249ee86364..8ed48ff351cc 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -200,7 +200,6 @@ config BLK_DEV_DM_BUILTIN
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 794811875732..5d51c5ef678b 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -27,16 +27,30 @@ 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);
#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)
+{
+}
#endif

int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
@@ -75,10 +89,7 @@ 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);
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