[PATCH v8 2/8] dax: Introduce holder for dax_device

[Shiyang Ruan <ruansy.fnst@fujitsu.com>]

To easily track filesystem from a pmem device, we introduce a holder for
dax_device structure, and also its operation.  This holder is used to
remember who is using this dax_device:
 - When it is the backend of a filesystem, the holder will be the
   superblock of this filesystem.
 - When this pmem device is one of the targets in a mapped device, the
   holder will be this mapped device.  In this case, the mapped device
   has its own dax_device and it will follow the first rule.  So that we
   can finally track to the filesystem we needed.

The holder and holder_ops will be set when filesystem is being mounted,
or an target device is being activated.

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
 drivers/dax/super.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dax.h | 25 ++++++++++++++++++
 2 files changed, 88 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index f7701e943019..ed1b27198382 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -23,7 +23,10 @@
  * @cdev: optional character interface for "device dax"
  * @host: optional name for lookups where the device path is not available
  * @private: dax driver private data
+ * @holder_data: holder of a dax_device: could be filesystem or mapped device
  * @flags: state and boolean properties
+ * @ops: operations for dax_device
+ * @holder_ops: operations for the inner holder
  */
 struct dax_device {
 	struct hlist_node list;
@@ -32,8 +35,10 @@ struct dax_device {
 	const char *host;
 	void *private;
 	struct percpu_rw_semaphore rwsem;
+	void *holder_data;
 	unsigned long flags;
 	const struct dax_operations *ops;
+	const struct dax_holder_operations *holder_ops;
 };
 
 static dev_t dax_devt;
@@ -376,6 +381,29 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
 }
 EXPORT_SYMBOL_GPL(dax_zero_page_range);
 
+int dax_holder_notify_failure(struct dax_device *dax_dev, u64 off,
+			      u64 len, int mf_flags)
+{
+	int rc;
+
+	dax_read_lock(dax_dev);
+	if (!dax_alive(dax_dev)) {
+		rc = -ENXIO;
+		goto out;
+	}
+
+	if (!dax_dev->holder_ops) {
+		rc = -EOPNOTSUPP;
+		goto out;
+	}
+
+	rc = dax_dev->holder_ops->notify_failure(dax_dev, off, len, mf_flags);
+out:
+	dax_read_unlock(dax_dev);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dax_holder_notify_failure);
+
 #ifdef CONFIG_ARCH_HAS_PMEM_API
 void arch_wb_cache_pmem(void *addr, size_t size);
 void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
@@ -438,6 +466,10 @@ void kill_dax(struct dax_device *dax_dev)
 		return;
 	dax_write_lock(dax_dev);
 	clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
+
+	/* clear holder data */
+	dax_dev->holder_ops = NULL;
+	dax_dev->holder_data = NULL;
 	dax_write_unlock(dax_dev);
 
 	spin_lock(&dax_host_lock);
@@ -622,6 +654,37 @@ void put_dax(struct dax_device *dax_dev)
 }
 EXPORT_SYMBOL_GPL(put_dax);
 
+void dax_set_holder(struct dax_device *dax_dev, void *holder,
+		const struct dax_holder_operations *ops)
+{
+	dax_write_lock(dax_dev);
+	if (!dax_alive(dax_dev)) {
+		dax_write_unlock(dax_dev);
+		return;
+	}
+
+	dax_dev->holder_data = holder;
+	dax_dev->holder_ops = ops;
+	dax_write_unlock(dax_dev);
+}
+EXPORT_SYMBOL_GPL(dax_set_holder);
+
+void *dax_get_holder(struct dax_device *dax_dev)
+{
+	void *holder;
+
+	dax_read_lock(dax_dev);
+	if (!dax_alive(dax_dev)) {
+		dax_read_unlock(dax_dev);
+		return NULL;
+	}
+
+	holder = dax_dev->holder_data;
+	dax_read_unlock(dax_dev);
+	return holder;
+}
+EXPORT_SYMBOL_GPL(dax_get_holder);
+
 /**
  * inode_dax: convert a public inode into its dax_dev
  * @inode: An inode with i_cdev pointing to a dax_dev
diff --git a/include/linux/dax.h b/include/linux/dax.h
index e38711d6c519..891c3e8a40e6 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -38,9 +38,24 @@ struct dax_operations {
 	int (*zero_page_range)(struct dax_device *, pgoff_t, size_t);
 };
 
+struct dax_holder_operations {
+	/*
+	 * notify_failure - notify memory failure into inner holder device
+	 * @dax_dev: the dax device which contains the holder
+	 * @offset: offset on this dax device where memory failure occurs
+	 * @len: length of this memory failure event
+	 * @flags: action flags for memory failure handler
+	 */
+	int (*notify_failure)(struct dax_device *dax_dev, u64 offset,
+			u64 len, int mf_flags);
+};
+
 extern struct attribute_group dax_attribute_group;
 
 #if IS_ENABLED(CONFIG_DAX)
+void dax_set_holder(struct dax_device *dax_dev, void *holder,
+		const struct dax_holder_operations *ops);
+void *dax_get_holder(struct dax_device *dax_dev);
 struct dax_device *alloc_dax(void *private, const char *host,
 		const struct dax_operations *ops, unsigned long flags);
 void put_dax(struct dax_device *dax_dev);
@@ -70,6 +85,14 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 	return dax_synchronous(dax_dev);
 }
 #else
+static inline void dax_set_holder(struct dax_device *dax_dev, void *holder,
+		const struct dax_holder_operations *ops)
+{
+}
+static inline void *dax_get_holder(struct dax_device *dax_dev)
+{
+	return NULL;
+}
 static inline struct dax_device *alloc_dax(void *private, const char *host,
 		const struct dax_operations *ops, unsigned long flags)
 {
@@ -198,6 +221,8 @@ size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
 		size_t bytes, struct iov_iter *i);
 int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
 			size_t nr_pages);
+int dax_holder_notify_failure(struct dax_device *dax_dev, u64 off, u64 len,
+		int mf_flags);
 void dax_flush(struct dax_device *dax_dev, void *addr, size_t size);
 
 ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
-- 
2.33.0