Re: [PATCH 2/3] fs: add STATX_DIO_READ_ALIGN

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Aug 28, 2024 at 08:11:02AM +0300, Christoph Hellwig wrote:
> Add a separate dio read align field, as many out of place write
> file systems can easily do reads aligned to the device sector size,
> but require bigger alignment for writes.
> 
> This is usually papered over by falling back to buffered I/O for smaller
> writes and doing read-modify-write cycles, but performance for this
> sucks, so applications benefit from knowing the actual write alignment.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks fine to me...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/stat.c                 | 1 +
>  include/linux/stat.h      | 1 +
>  include/uapi/linux/stat.h | 4 +++-
>  3 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/stat.c b/fs/stat.c
> index 89ce1be563108c..044e7ad9f3abc2 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> @@ -700,6 +700,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
>  	tmp.stx_mnt_id = stat->mnt_id;
>  	tmp.stx_dio_mem_align = stat->dio_mem_align;
>  	tmp.stx_dio_offset_align = stat->dio_offset_align;
> +	tmp.stx_dio_read_offset_align = stat->dio_read_offset_align;
>  	tmp.stx_subvol = stat->subvol;
>  	tmp.stx_atomic_write_unit_min = stat->atomic_write_unit_min;
>  	tmp.stx_atomic_write_unit_max = stat->atomic_write_unit_max;
> diff --git a/include/linux/stat.h b/include/linux/stat.h
> index 3d900c86981c5b..9d8382e23a9c69 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -52,6 +52,7 @@ struct kstat {
>  	u64		mnt_id;
>  	u32		dio_mem_align;
>  	u32		dio_offset_align;
> +	u32		dio_read_offset_align;
>  	u64		change_cookie;
>  	u64		subvol;
>  	u32		atomic_write_unit_min;
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 8b35d7d511a287..f78ee3670dd5d7 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -179,7 +179,8 @@ struct statx {
>  	/* Max atomic write segment count */
>  	__u32   stx_atomic_write_segments_max;
>  
> -	__u32   __spare1[1];
> +	/* File offset alignment for direct I/O reads */
> +	__u32	stx_dio_read_offset_align;
>  
>  	/* 0xb8 */
>  	__u64	__spare3[9];	/* Spare space for future expansion */
> @@ -213,6 +214,7 @@ struct statx {
>  #define STATX_MNT_ID_UNIQUE	0x00004000U	/* Want/got extended stx_mount_id */
>  #define STATX_SUBVOL		0x00008000U	/* Want/got stx_subvol */
>  #define STATX_WRITE_ATOMIC	0x00010000U	/* Want/got atomic_write_* fields */
> +#define STATX_DIO_READ_ALIGN	0x00020000U	/* Want/got dio read alignment info */
>  
>  #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
>  
> -- 
> 2.43.0
> 
>