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

Ritesh Harjani
2024-02-24T18:47:04Z

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