On Fri, Jul 30, 2021 at 3:02 AM Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxx>
> ---
> drivers/dax/super.c | 46 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/dax.h | 17 +++++++++++++++++
> 2 files changed, 63 insertions(+)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 5fa6ae9dbc8b..00c32dfa5665 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -214,6 +214,8 @@ enum dax_device_flags {
> * @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_rwsem: prevent unregistration while holder_ops is in progress
> + * @holder_data: holder of a dax_device: could be filesystem or mapped device
> * @flags: state and boolean properties
> */
> struct dax_device {
> @@ -222,8 +224,11 @@ struct dax_device {
> struct cdev cdev;
> const char *host;
> void *private;
> + struct rw_semaphore holder_rwsem;
Given the rarity of notification failures and the infrequency of
registration events I think it would be ok for this to be a global
lock rather than per-device. In fact there is already a global dax
lock, see dax_read_lock(). Let's convert that from srcu to rwsem and
add a dax_write_lock().
> + 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 +378,25 @@ 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;
> +
> + if (!dax_dev)
> + return -ENXIO;
There also needs to be a dax_dev->alive check, which is only valid to
be checked under dax_read_lock().
Who would ever pass NULL to this function?
> +
> + if (!dax_dev->holder_data)
> + return -EOPNOTSUPP;
> +
> + down_read(&dax_dev->holder_rwsem);
> + rc = dax_dev->holder_ops->notify_failure(dax_dev, offset,
> + size, data);
> + up_read(&dax_dev->holder_rwsem);
> + 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 +627,7 @@ 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 +649,27 @@ 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)
Same questions about NULL dax dev and ->alive checking.
> + 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)
> +{
> + if (!dax_dev)
> + return NULL;
Where is this API used? This result is not valid unless the caller is
holding the read lock.
> +
> + return dax_dev->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,
> --
> 2.32.0
>
>
>
