dax: Add fs_dax_get() func to prepare dax for fs-dax usage

The fs_dax_get() function should be called by fs-dax file systems after
opening a fsdev dax device. This adds holder_operations, which provides
a memory failure callback path and effects exclusivity between callers
of fs_dax_get().

fs_dax_get() is specific to fsdev_dax, so it checks the driver type
(which required touching bus.[ch]). fs_dax_get() fails if fsdev_dax is
not bound to the memory.

This function serves the same role as fs_dax_get_by_bdev(), which dax
file systems call after opening the pmem block device.

This can't be located in fsdev.c because struct dax_device is opaque
there.

This will be called by fs/fuse/famfs.c in a subsequent commit.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: John Groves <john@groves.net>
Link: https://patch.msgid.link/0100019d311d8750-75395c22-031b-4d5f-aebe-790dca656b87-000000@email.amazonses.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 1b412264bb365d997d86b0ac114f24f3f62ccf88..32f7b7702c28be5372513d2ffe42aa22126bd415 100644 (file)
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -39,8 +39,6 @@ static int dax_bus_uevent(const struct device *dev, struct kobj_uevent_env *env)
        return add_uevent_var(env, "MODALIAS=" DAX_DEVICE_MODALIAS_FMT, 0);
 }
 
-#define to_dax_drv(__drv)      container_of_const(__drv, struct dax_device_driver, drv)
-
 static struct dax_id *__dax_match_id(const struct dax_device_driver *dax_drv,
                const char *dev_name)
 {

diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
index 880bdf7e72d7619ee3bbe2dcd4046bd29a4c5eab..dc6f112ac4a4b194df3eb13e2431962b285d1a3e 100644 (file)
--- a/drivers/dax/bus.h
+++ b/drivers/dax/bus.h
@@ -42,6 +42,8 @@ struct dax_device_driver {
        void (*remove)(struct dev_dax *dev);
 };
 
+#define to_dax_drv(__drv) container_of_const(__drv, struct dax_device_driver, drv)
+
 int __dax_driver_register(struct dax_device_driver *dax_drv,
                struct module *module, const char *mod_name);
 #define dax_driver_register(driver) \

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index ba0b4cd18a77aba6c7d99ca7cded484f8d950964..d4ab60c406bf8de11994cb3c98e64ec2dc477c54 100644 (file)
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -14,6 +14,7 @@
 #include <linux/fs.h>
 #include <linux/cacheinfo.h>
 #include "dax-private.h"
+#include "bus.h"
 
 /**
  * struct dax_device - anchor object for dax services
@@ -111,6 +112,10 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, u64 *start_off,
 }
 EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
 
+#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
+
+#if IS_ENABLED(CONFIG_FS_DAX)
+
 void fs_put_dax(struct dax_device *dax_dev, void *holder)
 {
        if (dax_dev && holder &&
@@ -119,7 +124,66 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
        put_dax(dax_dev);
 }
 EXPORT_SYMBOL_GPL(fs_put_dax);
-#endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
+
+/**
+ * fs_dax_get() - get ownership of a devdax via holder/holder_ops
+ *
+ * fs-dax file systems call this function to prepare to use a devdax device for
+ * fsdax. This is like fs_dax_get_by_bdev(), but the caller already has struct
+ * dev_dax (and there is no bdev). The holder makes this exclusive.
+ *
+ * @dax_dev: dev to be prepared for fs-dax usage
+ * @holder: filesystem or mapped device inside the dax_device
+ * @hops: operations for the inner holder
+ *
+ * Returns: 0 on success, <0 on failure
+ */
+int fs_dax_get(struct dax_device *dax_dev, void *holder,
+       const struct dax_holder_operations *hops)
+{
+       struct dev_dax *dev_dax;
+       struct dax_device_driver *dax_drv;
+       int id;
+
+       id = dax_read_lock();
+       if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode)) {
+               dax_read_unlock(id);
+               return -ENODEV;
+       }
+       dax_read_unlock(id);
+
+       /* Verify the device is bound to fsdev_dax driver */
+       dev_dax = dax_get_private(dax_dev);
+       if (!dev_dax) {
+               iput(&dax_dev->inode);
+               return -ENODEV;
+       }
+
+       device_lock(&dev_dax->dev);
+       if (!dev_dax->dev.driver) {
+               device_unlock(&dev_dax->dev);
+               iput(&dax_dev->inode);
+               return -ENODEV;
+       }
+       dax_drv = to_dax_drv(dev_dax->dev.driver);
+       if (dax_drv->type != DAXDRV_FSDEV_TYPE) {
+               device_unlock(&dev_dax->dev);
+               iput(&dax_dev->inode);
+               return -EOPNOTSUPP;
+       }
+       device_unlock(&dev_dax->dev);
+
+       if (cmpxchg(&dax_dev->holder_data, NULL, holder)) {
+               iput(&dax_dev->inode);
+               return -EBUSY;
+       }
+
+       dax_dev->holder_ops = hops;
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(fs_dax_get);
+#endif /* CONFIG_FS_DAX */
 
 enum dax_device_flags {
        /* !alive + rcu grace period == no new operations / mappings */

diff --git a/include/linux/dax.h b/include/linux/dax.h
index b19bfe0c2fd139f3bf5de58d807ebcf0f78d3585..a85e270bfb3c67a6ee0602f2afd99646828fc279 100644 (file)
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -130,7 +130,6 @@ int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk);
 void dax_remove_host(struct gendisk *disk);
 struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev, u64 *start_off,
                void *holder, const struct dax_holder_operations *ops);
-void fs_put_dax(struct dax_device *dax_dev, void *holder);
 #else
 static inline int dax_add_host(struct dax_device *dax_dev, struct gendisk *disk)
 {
@@ -145,12 +144,12 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev,
 {
        return NULL;
 }
-static inline void fs_put_dax(struct dax_device *dax_dev, void *holder)
-{
-}
 #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
 
 #if IS_ENABLED(CONFIG_FS_DAX)
+void fs_put_dax(struct dax_device *dax_dev, void *holder);
+int fs_dax_get(struct dax_device *dax_dev, void *holder,
+              const struct dax_holder_operations *hops);
 int dax_writeback_mapping_range(struct address_space *mapping,
                struct dax_device *dax_dev, struct writeback_control *wbc);
 int dax_folio_reset_order(struct folio *folio);
@@ -164,6 +163,15 @@ dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
 void dax_unlock_mapping_entry(struct address_space *mapping,
                unsigned long index, dax_entry_t cookie);
 #else
+static inline void fs_put_dax(struct dax_device *dax_dev, void *holder)
+{
+}
+
+static inline int fs_dax_get(struct dax_device *dax_dev, void *holder,
+                            const struct dax_holder_operations *hops)
+{
+       return -EOPNOTSUPP;
+}
 static inline struct page *dax_layout_busy_page(struct address_space *mapping)
 {
        return NULL;