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

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Message-ID: <ZdPWGwntYMvstbpc@dread.disaster.area>
Date: Tue, 20 Feb 2024 09:28:43 +1100
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, kbusch@...nel.org, hch@....de, sagi@...mberg.me,
	jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
	viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
	jack@...e.cz, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
	linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com,
	linux-aio@...ck.org, linux-btrfs@...r.kernel.org,
	io-uring@...r.kernel.org, nilay@...ux.ibm.com,
	ritesh.list@...il.com,
	Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH v4 04/11] fs: Add initial atomic write support info to
 statx

On Mon, Feb 19, 2024 at 01:01:02PM +0000, John Garry wrote:
> From: Prasad Singamsetty <prasad.singamsetty@...cle.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@...cle.com>
> #jpg: relocate bdev support to another patch
> Signed-off-by: John Garry <john.g.garry@...cle.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_max:	Maximum supported atomic write length
> + *
> + * 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(generic_fill_statx_atomic_writes);

What units are these in? Nothing in the patch or commit description
tells us....

-Dave.
-- 
Dave Chinner
david@...morbit.com