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 <redacted>
---
 drivers/dax/super.c | 61 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dax.h | 25 +++++++++++++++++++
 2 files changed, 86 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 719e77b2c2d4..a19fcc0a54f3 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c

@@ -20,15 +20,20 @@
  * @inode: core vfs
  * @cdev: optional character interface for "device dax"
  * @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 inode inode;
        struct cdev cdev;
        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;

@@ -190,6 +195,29 @@ 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)

@@ -252,6 +280,10 @@ 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);
 }
 EXPORT_SYMBOL_GPL(kill_dax);

@@ -399,6 +431,35 @@ 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))
+               goto out;
+
+       dax_dev->holder_data = holder;
+       dax_dev->holder_ops = ops;
+out:
+       dax_write_unlock(dax_dev);

+}
+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 8414a08dcbea..f01684a63447 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h

@@ -44,6 +44,21 @@ struct dax_operations {
 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *alloc_dax(void *private, const struct dax_operations *ops,
                unsigned long flags);
+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);
+};
+
+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);
 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);

@@ -71,6 +86,14 @@ 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 struct dax_operations *ops, unsigned long flags)
 {

@@ -199,6 +222,8 @@ 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,
--

2.34.0