[PATCH v4 04/11] fs: Add initial atomic write support info to statx

[Dave Chinner]

On Mon, Feb 19, 2024 at 01:01:02PM +0000, John Garry wrote:
> From: Prasad Singamsetty <prasad.singamsetty at oracle.com>
> 
> Extend statx system call to return additional info for atomic write support
> support for a file.
> 
> Helper function generic_fill_statx_atomic_writes() can be used by FSes to
> fill in the relevant statx fields.
> 
> Signed-off-by: Prasad Singamsetty <prasad.singamsetty at oracle.com>
> #jpg: relocate bdev support to another patch
> Signed-off-by: John Garry <john.g.garry at oracle.com>
> ---
>  fs/stat.c                 | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/fs.h        |  3 +++
>  include/linux/stat.h      |  3 +++
>  include/uapi/linux/stat.h |  9 ++++++++-
>  4 files changed, 48 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/stat.c b/fs/stat.c
> index 77cdc69eb422..522787a4ab6a 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -89,6 +89,37 @@ void generic_fill_statx_attr(struct inode *inode, struct kstat *stat)
>  }
>  EXPORT_SYMBOL(generic_fill_statx_attr);
>  
> +/**
> + * generic_fill_statx_atomic_writes - Fill in the atomic writes statx attributes
> + * @stat:	Where to fill in the attribute flags
> + * @unit_min:	Minimum supported atomic write length
> + * @unit_max:	Maximum supported atomic write length
> + *
> + * Fill in the STATX{_ATTR}_WRITE_ATOMIC flags in the kstat structure from
> + * atomic write unit_min and unit_max values.
> + */
> +void generic_fill_statx_atomic_writes(struct kstat *stat,
> +				      unsigned int unit_min,
> +				      unsigned int unit_max)
> +{
> +	/* Confirm that the request type is known */
> +	stat->result_mask |= STATX_WRITE_ATOMIC;
> +
> +	/* Confirm that the file attribute type is known */
> +	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
> +
> +	if (unit_min) {
> +		stat->atomic_write_unit_min = unit_min;
> +		stat->atomic_write_unit_max = unit_max;
> +		/* Initially only allow 1x segment */
> +		stat->atomic_write_segments_max = 1;
> +
> +		/* Confirm atomic writes are actually supported */
> +		stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
> +	}
> +}
> +EXPORT_SYMBOL(generic_fill_statx_atomic_writes);

What units are these in? Nothing in the patch or commit description
tells us....

-Dave.
-- 
Dave Chinner
david at fromorbit.com