Re: [PATCH v8 04/10] fs: Add initial atomic write support info to statx

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

On Mon, Jun 10, 2024 at 10:43:23AM +0000, John Garry wrote:
> From: Prasad Singamsetty <prasad.singamsetty@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. For now atomic_write_segments_max will
> always be 1, otherwise some rules would need to be imposed on iovec length
> and alignment, which we don't want now.
> 
> Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
> jpg: relocate bdev support to another patch
> Signed-off-by: John Garry <john.g.garry@oracle.com>

Looks fine to me, assuming there's a manpage update lurking somewhere?
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/stat.c                 | 34 ++++++++++++++++++++++++++++++++++
>  include/linux/fs.h        |  3 +++
>  include/linux/stat.h      |  3 +++
>  include/uapi/linux/stat.h | 12 ++++++++++--
>  4 files changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/stat.c b/fs/stat.c
> index 70bd3e888cfa..72d0e6357b91 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 atomic writes statx attributes
> + * @stat:	Where to fill in the attribute flags
> + * @unit_min:	Minimum supported atomic write length in bytes
> + * @unit_max:	Maximum supported atomic write length in bytes
> + *
> + * 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_GPL(generic_fill_statx_atomic_writes);
> +
>  /**
>   * vfs_getattr_nosec - getattr without security checks
>   * @path: file to get attributes from
> @@ -659,6 +690,9 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
>  	tmp.stx_dio_mem_align = stat->dio_mem_align;
>  	tmp.stx_dio_offset_align = stat->dio_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;
> +	tmp.stx_atomic_write_segments_max = stat->atomic_write_segments_max;
>  
>  	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
>  }
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e049414bef7d..db26b4a70c62 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3235,6 +3235,9 @@ extern const struct inode_operations page_symlink_inode_operations;
>  extern void kfree_link(void *);
>  void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *);
>  void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
> +void generic_fill_statx_atomic_writes(struct kstat *stat,
> +				      unsigned int unit_min,
> +				      unsigned int unit_max);
>  extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);
>  extern int vfs_getattr(const struct path *, struct kstat *, u32, unsigned int);
>  void __inode_add_bytes(struct inode *inode, loff_t bytes);
> diff --git a/include/linux/stat.h b/include/linux/stat.h
> index bf92441dbad2..3d900c86981c 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -54,6 +54,9 @@ struct kstat {
>  	u32		dio_offset_align;
>  	u64		change_cookie;
>  	u64		subvol;
> +	u32		atomic_write_unit_min;
> +	u32		atomic_write_unit_max;
> +	u32		atomic_write_segments_max;
>  };
>  
>  /* These definitions are internal to the kernel for now. Mainly used by nfsd. */
> diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> index 67626d535316..887a25286441 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -126,9 +126,15 @@ struct statx {
>  	__u64	stx_mnt_id;
>  	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
>  	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
> -	__u64	stx_subvol;	/* Subvolume identifier */
>  	/* 0xa0 */
> -	__u64	__spare3[11];	/* Spare space for future expansion */
> +	__u64	stx_subvol;	/* Subvolume identifier */
> +	__u32	stx_atomic_write_unit_min;	/* Min atomic write unit in bytes */
> +	__u32	stx_atomic_write_unit_max;	/* Max atomic write unit in bytes */
> +	/* 0xb0 */
> +	__u32   stx_atomic_write_segments_max;	/* Max atomic write segment count */
> +	__u32   __spare1[1];
> +	/* 0xb8 */
> +	__u64	__spare3[9];	/* Spare space for future expansion */
>  	/* 0x100 */
>  };
>  
> @@ -157,6 +163,7 @@ struct statx {
>  #define STATX_DIOALIGN		0x00002000U	/* Want/got direct I/O alignment info */
>  #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__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
>  
> @@ -192,6 +199,7 @@ struct statx {
>  #define STATX_ATTR_MOUNT_ROOT		0x00002000 /* Root of a mount */
>  #define STATX_ATTR_VERITY		0x00100000 /* [I] Verity protected file */
>  #define STATX_ATTR_DAX			0x00200000 /* File is currently in DAX state */
> +#define STATX_ATTR_WRITE_ATOMIC		0x00400000 /* File supports atomic write operations */
>  
>  
>  #endif /* _UAPI_LINUX_STAT_H */
> -- 
> 2.31.1
> 
>