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

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

John Garry <john.g.garry@oracle.com> writes:

> 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.
>
> Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
> #jpg: relocate bdev support to another patch

^^^ miss maybe?
> Signed-off-by: John Garry <john.g.garry@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_min:	Minimum supported atomic write length in bytes


> + * @unit_max:	Maximum supported atomic write length
+ * @unit_max:	Maximum supported atomic write length in bytes

mentioning unit of the length might be useful here.

> + *
> + * 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,

This (unit_min) can still go above in the same line.

> +				      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;

Please log info about this in commit message about where this limit came
from? Is it since we only support ubuf (which IIUC, only supports 1
segment)? Later when we will add support for iovec, this limit can be
lifted?

> +
> +		/* Confirm atomic writes are actually supported */
> +		stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
> +	}
> +}
> +EXPORT_SYMBOL(generic_fill_statx_atomic_writes);
> +
>  /**
>   * vfs_getattr_nosec - getattr without security checks
>   * @path: file to get attributes from
> @@ -658,6 +689,9 @@ 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_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 7271640fd600..531140a7e27a 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3167,6 +3167,9 @@ 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);

We can make 80 col. width even with unit_min in the same first line as of *stat.


>  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 52150570d37a..2c5e2b8c6559 100644
> --- a/include/linux/stat.h
> +++ b/include/linux/stat.h
> @@ -53,6 +53,9 @@ struct kstat {
>  	u32		dio_mem_align;
>  	u32		dio_offset_align;
>  	u64		change_cookie;
> +	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 2f2ee82d5517..c0e8e10d1de6 100644
> --- a/include/uapi/linux/stat.h
> +++ b/include/uapi/linux/stat.h
> @@ -127,7 +127,12 @@ struct statx {
>  	__u32	stx_dio_mem_align;	/* Memory buffer alignment for direct I/O */
>  	__u32	stx_dio_offset_align;	/* File offset alignment for direct I/O */
>  	/* 0xa0 */
> -	__u64	__spare3[12];	/* Spare space for future expansion */
> +	__u32	stx_atomic_write_unit_min;
> +	__u32	stx_atomic_write_unit_max;
> +	__u32   stx_atomic_write_segments_max;

Let's add one liner for each of these fields similar to how it was done
for others?

/* Minimum supported atomic write length in bytes */
/* Maximum supported atomic write length in bytes */
/* Maximum no. of segments (iovecs?) supported for atomic write */


> +	__u32   __spare1;
> +	/* 0xb0 */
> +	__u64	__spare3[10];	/* Spare space for future expansion */
>  	/* 0x100 */
>  };
>  
> @@ -155,6 +160,7 @@ struct statx {
>  #define STATX_MNT_ID		0x00001000U	/* Got stx_mnt_id */
>  #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_WRITE_ATOMIC	0x00008000U	/* Want/got atomic_write_* fields */
>  
>  #define STATX__RESERVED		0x80000000U	/* Reserved for future struct statx expansion */
>  
> @@ -190,6 +196,7 @@ 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