On Thu, 3 Jul 2025 13:50:16 -0500
John Groves <John@Groves.net> wrote:
> This function should be called by fs-dax file systems after opening the
> devdax device. This adds holder_operations, which effects exclusivity
> between callers of fs_dax_get().
>
> This function serves the same role as fs_dax_get_by_bdev(), which dax
> file systems call after opening the pmem block device.
>
> This also adds the CONFIG_DEV_DAX_IOMAP Kconfig parameter
>
> Signed-off-by: John Groves <john@groves.net>
Trivial stuff inline.
> ---
> drivers/dax/Kconfig | 6 ++++++
> drivers/dax/super.c | 30 ++++++++++++++++++++++++++++++
> include/linux/dax.h | 5 +++++
> 3 files changed, 41 insertions(+)
>
> diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
> index d656e4c0eb84..ad19fa966b8b 100644
> --- a/drivers/dax/Kconfig
> +++ b/drivers/dax/Kconfig
> @@ -78,4 +78,10 @@ config DEV_DAX_KMEM
>
> Say N if unsure.
>
> +config DEV_DAX_IOMAP
> + depends on DEV_DAX && DAX
> + def_bool y
> + help
> + Support iomap mapping of devdax devices (for FS-DAX file
> + systems that reside on character /dev/dax devices)
> endif
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index e16d1d40d773..48bab9b5f341 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -122,6 +122,36 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
> EXPORT_SYMBOL_GPL(fs_put_dax);
> #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
>
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +/**
> + * fs_dax_get()
Trivial but from what I recall kernel-doc isn't going to like this.
Needs a short description.
> + *
> + * 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.
there is no *bdev? So * in wrong place.
> + *
> + * @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)
> +{
> + if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
> + return -ENODEV;
> +
> + if (cmpxchg(&dax_dev->holder_data, NULL, holder))
> + return -EBUSY;
> +
> + dax_dev->holder_ops = hops;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_get);
> +#endif /* DEV_DAX_IOMAP */
> +
> enum dax_device_flags {
> /* !alive + rcu grace period == no new operations / mappings */
> DAXDEV_ALIVE,
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index df41a0017b31..86bf5922f1b0 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -51,6 +51,11 @@ struct dax_holder_operations {
>
> #if IS_ENABLED(CONFIG_DAX)
> struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
> +
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +int fs_dax_get(struct dax_device *dax_dev, void *holder, const struct dax_holder_operations *hops);
> +struct dax_device *inode_dax(struct inode *inode);
> +#endif
> void *dax_holder(struct dax_device *dax_dev);
> void put_dax(struct dax_device *dax_dev);
> void kill_dax(struct dax_device *dax_dev);