Re: [PATCH v5 01/10] dax: add fsdev_dax_from_file()

[Dave Jiang <dave.jiang@intel.com>]

On 10/16/26 8:16 AM, Miklos Szeredi wrote:
> From: John Groves <John@Groves.net>
> 
> If the file is a fsdev_dax open, take the dax_dev from the device inode's
> i_cdev.  Return with a reference grabbed on the private dax inode.
> 
> Make dax_dev_get() static again (internal to super.c for alloc_dax), export
> fsdev_dax_from_file() instead.
> 
> This fix is in response to a Sashiko review, and some subsequent analysis.
> 
> About the 'fixes' tag: this removes the export of dax_dev_get(), which was
> flawed, and replaces it with fsdev_dax_from_file(). It feels like the fixes
> tag makes sense for correcting an ABI error.
> 
> Fixes: 2ae624d5a555d ("dax: export dax_dev_get()")
> Originally-by: John Groves <john@groves.net>
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/dax/fsdev.c | 23 +++++++++++++++++++++++
>  drivers/dax/super.c |  3 +--
>  include/linux/dax.h |  3 ++-
>  3 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
> index 598604bf5ac5..910665c1f492 100644
> --- a/drivers/dax/fsdev.c
> +++ b/drivers/dax/fsdev.c
> @@ -234,6 +234,29 @@ static const struct file_operations fsdev_fops = {
>  	.release = fsdev_release,
>  };
>  
> +/**
> + * fsdev_dax_from_file - get dax_device from an open file
> + * @file: open device file
> + *
> + * Returns a dax_device pointer if @file refers to a fsdev_dax device.
> + * Otherwise return NULL.
> + *
> + * Caller must put_dax() the returned device when done.
> + */
> +struct dax_device *fsdev_dax_from_file(struct file *file)
> +{
> +	struct dax_device *dax_dev;
> +
> +	if (file->f_op != &fsdev_fops)
> +		return NULL;
> +
> +	dax_dev = inode_dax(file_inode(file));
> +	ihold(dax_inode(dax_dev));
> +
> +	return dax_dev;
> +}
> +EXPORT_SYMBOL_GPL(fsdev_dax_from_file);
> +
>  /*
>   * Acquire the dev_pagemap for probe: the static (pre-populated) one if
>   * present, or a devm-allocated one for the dynamic case. Note that
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 45f84b0eb909..25836f389bde 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -565,7 +565,7 @@ static int dax_set(struct inode *inode, void *data)
>  	return 0;
>  }
>  
> -struct dax_device *dax_dev_get(dev_t devt)
> +static struct dax_device *dax_dev_get(dev_t devt)
>  {
>  	struct dax_device *dax_dev;
>  	struct inode *inode;
> @@ -588,7 +588,6 @@ struct dax_device *dax_dev_get(dev_t devt)
>  
>  	return dax_dev;
>  }
> -EXPORT_SYMBOL_GPL(dax_dev_get);
>  
>  struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
>  {
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index fe6c3ded1b50..2c9fc81f031b 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -54,7 +54,6 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
>  void *dax_holder(struct dax_device *dax_dev);
>  void put_dax(struct dax_device *dax_dev);
>  void kill_dax(struct dax_device *dax_dev);
> -struct dax_device *dax_dev_get(dev_t devt);
>  void dax_write_cache(struct dax_device *dax_dev, bool wc);
>  bool dax_write_cache_enabled(struct dax_device *dax_dev);
>  bool dax_synchronous(struct dax_device *dax_dev);
> @@ -323,3 +322,5 @@ typedef int (*walk_hmem_fn)(struct device *dev, int target_nid,
>  			    const struct resource *res);
>  int walk_hmem_resources(struct device *dev, walk_hmem_fn fn);
>  #endif
> +
> +struct dax_device *fsdev_dax_from_file(struct file *file);