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

[John Garry <john.g.garry@oracle.com>]

On 12/06/2024 21:54, Darrick J. Wong wrote:
> 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?

Sure, see 
https://lore.kernel.org/lkml/20240124112731.28579-1-john.g.garry@oracle.com/T/#m520dca97a9748de352b5a723d3155a4bb1e46456

I'll post a rebase, but the API is still the same.

> Reviewed-by: Darrick J. Wong <djwong@kernel.org>

Thanks,
John

> 
> --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
>>
>>