linux-kernel - Re: [PATCH 02/20] block, blksnap: header file of the module interface

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Date:   Wed, 6 Jul 2022 06:03:53 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sergei Shtepa <sergei.shtepa@...am.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/20] block, blksnap: header file of the module interface

On Mon, Jun 13, 2022 at 06:52:55PM +0300, Sergei Shtepa wrote:
> The header file contains a set of declarations, structures and control
> requests (ioctl) that allows to manage the module from the user space.

I think this should go into include/uapi/ if you want it in a global
place.

> +#pragma once

In the kernel we use classic #ifdef based guards.

> +#include <linux/types.h>
> +#include <linux/uuid.h>

The uuid_t type can't be used in a userspae API.  Please use a raw
__u8 API and then use import_uuid.

> +#define BLK_SNAP_MODULE_NAME "blksnap"

Does this belong into a user interface?

> +#define BLK_SNAP_IMAGE_NAME "blksnap-image"
> +#define BLK_SNAP 'V'
> +
> +enum blk_snap_ioctl {
> +	/*
> +	 * Service controls
> +	 */
> +	blk_snap_ioctl_version,
> +	/*
> +	 * Contols for tracking
> +	 */
> +	blk_snap_ioctl_tracker_remove,
> +	blk_snap_ioctl_tracker_collect,
> +	blk_snap_ioctl_tracker_read_cbt_map,
> +	blk_snap_ioctl_tracker_mark_dirty_blocks,
> +	/*
> +	 * Snapshot contols
> +	 */
> +	blk_snap_ioctl_snapshot_create,
> +	blk_snap_ioctl_snapshot_destroy,
> +	blk_snap_ioctl_snapshot_append_storage,
> +	blk_snap_ioctl_snapshot_take,
> +	blk_snap_ioctl_snapshot_collect,
> +	blk_snap_ioctl_snapshot_collect_images,
> +	blk_snap_ioctl_snapshot_wait_event,
> +	blk_snap_ioctl_end,

For uapis classic #defines have the adnvantage that userspace can test
for their presence if new ones get added.  Also the _end one should not
be in an UAPI header as new ones can be added at any time.