diff mbox series

[v5,2/9] dax: Introduce holder for dax_device

Message ID 20210628000218.387833-3-ruansy.fnst@fujitsu.com (mailing list archive)
State New, archived
Headers show
Series fsdax: introduce fs query to support reflink | expand

Commit Message

Shiyang Ruan June 28, 2021, 12:02 a.m. UTC 
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 | 49 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dax.h | 17 ++++++++++++++++
 2 files changed, 66 insertions(+)

--
2.32.0



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Comments

Christoph Hellwig July 19, 2021, 3:17 p.m. UTC | #1 
On Mon, Jun 28, 2021 at 08:02:11AM +0800, Shiyang Ruan wrote:
> +int dax_holder_notify_failure(struct dax_device *dax_dev, loff_t offset,
> +			      size_t size, void *data)
> +{
> +	int rc = -ENXIO;
> +	if (!dax_dev)
> +		return rc;
> +
> +	if (dax_dev->holder_data) {
> +		rc = dax_dev->holder_ops->notify_failure(dax_dev, offset,
> +							 size, data);
> +		if (rc == -ENODEV)
> +			rc = -ENXIO;
> +	} else
> +		rc = -EOPNOTSUPP;

The style looks a little odd.  Why not:

	if (!dax_dev)
		return -ENXIO
	if (!dax_dev->holder_data)
		return -EOPNOTSUPP;
	return dax_dev->holder_ops->notify_failure(dax_dev, offset, size, data);

and let everyone deal with the same errno codes?

Also why do we even need the dax_dev NULL check?

> +void dax_set_holder(struct dax_device *dax_dev, void *holder,
> +		const struct dax_holder_operations *ops)
> +{
> +	if (!dax_dev)
> +		return;

I don't think we really need that check here.

> +void *dax_get_holder(struct dax_device *dax_dev)
> +{
> +	void *holder_data;
> +
> +	if (!dax_dev)
> +		return NULL;

Same here.

> +
> +	down_read(&dax_dev->holder_rwsem);
> +	holder_data = dax_dev->holder_data;
> +	up_read(&dax_dev->holder_rwsem);
> +
> +	return holder_data;

That lock won't protect anything.  I think we simply must have
synchronization to prevent unregistration while the ->notify_failure
call is in progress.

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Shiyang Ruan July 20, 2021, 10:37 a.m. UTC | #2 
> -----Original Message-----
> Subject: Re: [PATCH v5 2/9] dax: Introduce holder for dax_device
> 
> On Mon, Jun 28, 2021 at 08:02:11AM +0800, Shiyang Ruan wrote:
> > +int dax_holder_notify_failure(struct dax_device *dax_dev, loff_t offset,
> > +			      size_t size, void *data)
> > +{
> > +	int rc = -ENXIO;
> > +	if (!dax_dev)
> > +		return rc;
> > +
> > +	if (dax_dev->holder_data) {
> > +		rc = dax_dev->holder_ops->notify_failure(dax_dev, offset,
> > +							 size, data);
> > +		if (rc == -ENODEV)
> > +			rc = -ENXIO;
> > +	} else
> > +		rc = -EOPNOTSUPP;
> 
> The style looks a little odd.  Why not:
> 
> 	if (!dax_dev)
> 		return -ENXIO
> 	if (!dax_dev->holder_data)
> 		return -EOPNOTSUPP;
> 	return dax_dev->holder_ops->notify_failure(dax_dev, offset, size, data);
> 
> and let everyone deal with the same errno codes?
OK.

> 
> Also why do we even need the dax_dev NULL check?

Because this dax_dev is obtain by fs_dax_get_by_bdev() in XFS and dax_get_by_host() in MD.  According to their definition, NULL may be returned.  So I check the dax_dev here.

> 
> > +void dax_set_holder(struct dax_device *dax_dev, void *holder,
> > +		const struct dax_holder_operations *ops) {
> > +	if (!dax_dev)
> > +		return;
> 
> I don't think we really need that check here.
> 
> > +void *dax_get_holder(struct dax_device *dax_dev) {
> > +	void *holder_data;
> > +
> > +	if (!dax_dev)
> > +		return NULL;
> 
> Same here.
> 
> > +
> > +	down_read(&dax_dev->holder_rwsem);
> > +	holder_data = dax_dev->holder_data;
> > +	up_read(&dax_dev->holder_rwsem);
> > +
> > +	return holder_data;
> 
> That lock won't protect anything.  I think we simply must have synchronization
> to prevent unregistration while the ->notify_failure call is in progress.

Yes, I misunderstood the purpose of the lock. I'll fix this.


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Ruan.

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diff mbox series

Patch

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 5fa6ae9dbc8b..22f0aa3f2e13 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -222,8 +222,11 @@  struct dax_device {
 	struct cdev cdev;
 	const char *host;
 	void *private;
+	struct rw_semaphore holder_rwsem;
+	void *holder_data;
 	unsigned long flags;
 	const struct dax_operations *ops;
+	const struct dax_holder_operations *holder_ops;
 };

 static ssize_t write_cache_show(struct device *dev,
@@ -373,6 +376,24 @@  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, loff_t offset,
+			      size_t size, void *data)
+{
+	int rc = -ENXIO;
+	if (!dax_dev)
+		return rc;
+
+	if (dax_dev->holder_data) {
+		rc = dax_dev->holder_ops->notify_failure(dax_dev, offset,
+							 size, data);
+		if (rc == -ENODEV)
+			rc = -ENXIO;
+	} else
+		rc = -EOPNOTSUPP;
+	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)
@@ -603,6 +624,7 @@  struct dax_device *alloc_dax(void *private, const char *__host,
 	dax_add_host(dax_dev, host);
 	dax_dev->ops = ops;
 	dax_dev->private = private;
+	init_rwsem(&dax_dev->holder_rwsem);
 	if (flags & DAXDEV_F_SYNC)
 		set_dax_synchronous(dax_dev);

@@ -624,6 +646,33 @@  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)
+{
+	if (!dax_dev)
+		return;
+	down_write(&dax_dev->holder_rwsem);
+	dax_dev->holder_data = holder;
+	dax_dev->holder_ops = ops;
+	up_write(&dax_dev->holder_rwsem);
+}
+EXPORT_SYMBOL_GPL(dax_set_holder);
+
+void *dax_get_holder(struct dax_device *dax_dev)
+{
+	void *holder_data;
+
+	if (!dax_dev)
+		return NULL;
+
+	down_read(&dax_dev->holder_rwsem);
+	holder_data = dax_dev->holder_data;
+	up_read(&dax_dev->holder_rwsem);
+
+	return holder_data;
+}
+EXPORT_SYMBOL_GPL(dax_get_holder);
+
 /**
  * dax_get_by_host() - temporary lookup mechanism for filesystem-dax
  * @host: alternate name for the device registered by a dax driver
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b52f084aa643..6f4b5c97ceb0 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -38,10 +38,17 @@  struct dax_operations {
 	int (*zero_page_range)(struct dax_device *, pgoff_t, size_t);
 };

+struct dax_holder_operations {
+	int (*notify_failure)(struct dax_device *, loff_t, size_t, void *);
+};
+
 extern struct attribute_group dax_attribute_group;

 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *dax_get_by_host(const char *host);
+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);
@@ -77,6 +84,14 @@  static inline struct dax_device *dax_get_by_host(const char *host)
 {
 	return NULL;
 }
+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)
 {
@@ -226,6 +241,8 @@  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, loff_t offset,
+		size_t size, void *data);
 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,