linux-kernel - Re: [PATCH 01/21] block: Add atomic write operations to request

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Date:   Thu, 9 Nov 2023 16:10:13 +0100
From:   Christoph Hellwig <hch@....de>
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,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org,
        Himanshu Madhani <himanshu.madhani@...cle.com>
Subject: Re: [PATCH 01/21] block: Add atomic write operations to
 request_queue limits

On Fri, Sep 29, 2023 at 10:27:06AM +0000, John Garry wrote:
> From: Himanshu Madhani <himanshu.madhani@...cle.com>
> 
> Add the following limits:
> - atomic_write_boundary_bytes
> - atomic_write_max_bytes
> - atomic_write_unit_max_bytes
> - atomic_write_unit_min_bytes
> 
> All atomic writes limits are initialised to 0 to indicate no atomic write
> support. Stacked devices are just not supported either for now.
> 
> Signed-off-by: Himanshu Madhani <himanshu.madhani@...cle.com>
> #jpg: Heavy rewrite
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  Documentation/ABI/stable/sysfs-block | 42 +++++++++++++++++++
>  block/blk-settings.c                 | 60 ++++++++++++++++++++++++++++
>  block/blk-sysfs.c                    | 33 +++++++++++++++
>  include/linux/blkdev.h               | 33 +++++++++++++++
>  4 files changed, 168 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
> index 1fe9a553c37b..05df7f74cbc1 100644
> --- a/Documentation/ABI/stable/sysfs-block
> +++ b/Documentation/ABI/stable/sysfs-block
> @@ -21,6 +21,48 @@ Description:
>  		device is offset from the internal allocation unit's
>  		natural alignment.
>  
> +What:		/sys/block/<disk>/atomic_write_max_bytes
> +Date:		May 2023
> +Contact:	Himanshu Madhani <himanshu.madhani@...cle.com>
> +Description:
> +		[RO] This parameter specifies the maximum atomic write
> +		size reported by the device. An atomic write operation
> +		must not exceed this number of bytes.

> +What:		/sys/block/<disk>/atomic_write_unit_max_bytes
> +Date:		January 2023
> +Contact:	Himanshu Madhani <himanshu.madhani@...cle.com>
> +Description:
> +		[RO] This parameter defines the largest block which can be
> +		written atomically with an atomic write operation. This
> +		value must be a multiple of atomic_write_unit_min and must
> +		be a power-of-two.

What is the difference between these two values?


> +Date:		May 2023
> +Contact:	Himanshu Madhani <himanshu.madhani@...cle.com>
> +Description:
> +		[RO] This parameter specifies the smallest block which can
> +		be written atomically with an atomic write operation. All
> +		atomic write operations must begin at a
> +		atomic_write_unit_min boundary and must be multiples of
> +		atomic_write_unit_min. This value must be a power-of-two.

How can the minimum unit be anythіng but one logical block?

> +extern void blk_queue_atomic_write_max_bytes(struct request_queue *q,
> +					     unsigned int bytes);

Please don't add pointless externs to prototypes in headers.

> +static inline unsigned int queue_atomic_write_unit_max_bytes(const struct request_queue *q)

.. and please avoid the overly long lines.