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

Darrick J. Wong
2024-06-12T20:54:34Z

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
>
>