Re: [PATCH 2/2] block: add BLKSETDESCZONE ioctl for Zoned Block Devices

From: Bart Van Assche <bvanassche@acm.org>
To: "Matias Bjørling" <matias.bjorling@wdc.com>,
	axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
	martin.petersen@oracle.com, damien.lemoal@wdc.com,
	niklas.cassel@wdc.com, hans.holmberg@wdc.com
Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: [PATCH 2/2] block: add BLKSETDESCZONE ioctl for Zoned Block Devices
Date: Sun, 28 Jun 2020 18:36:25 -0700	[thread overview]
Message-ID: <cbb91e7d-5cc8-eeb7-5219-b712545cb5c4@acm.org> (raw)
In-Reply-To: <20200628230102.26990-3-matias.bjorling@wdc.com>

On 2020-06-28 16:01, Matias Bjørling wrote:
> +	/* This may take a while, so be nice to others */
> +	cond_resched();
> +
> +	return submit_bio_wait(&bio);

A cond_resched() call before a submit_bio_wait() call? I think it's the
first time that I see this. Is that call really necessary? Isn't the
wait_for_completion() call inside submit_bio_wait() sufficient?

> +	/* no flags is currently supported */
                    ^^
                    are?

> +	/* allocate the size of the zone descriptor extension and fill
> +	 * with the data in the user data buffer. If the data size is less
> +	 * than the zone descriptor extension size, then the rest of the
> +	 * zone description extension data buffer is zero-filled.
> +	 */
> +	zsd_data = (void *) get_zeroed_page(GFP_KERNEL);
> +	if (!zsd_data)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(zsd_data, argp + sizeof(struct blk_zone_set_desc),
> +			   zsd.len)) {
> +		ret = -EFAULT;
> +		goto free;
> +	}

Has it been considered to use kmalloc() instead of get_zeroed_page()?

> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index ccb895f911b1..53b7b05b0004 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -316,6 +316,8 @@ enum req_opf {
>  	REQ_OP_ZONE_FINISH	= 12,
>  	/* write data at the current zone write pointer */
>  	REQ_OP_ZONE_APPEND	= 13,
> +	/* associate zone desc extension data to a zone */
> +	REQ_OP_ZONE_SET_DESC	= 14,
>  
>  	/* SCSI passthrough using struct scsi_request */
>  	REQ_OP_SCSI_IN		= 32,

Does REQ_OP_ZONE_SET_DESC count as a read or as a write operation? See also:

static inline bool op_is_write(unsigned int op)
{
	return (op & 1);
}

> +/**
> + * struct blk_zone_set_desc - BLKSETDESCZONE ioctl requests
> + * @sector: Starting sector of the zone to operate on.
> + * @flags: Feature flags.
> + * @len: size, in bytes, of the data to be associated to the zone.
> + * @data: data to be associated.
> + */
> +struct blk_zone_set_desc {
> +	__u64		sector;
> +	__u32		flags;
> +	__u32		len;
> +	__u8		data[0];
> +};

Isn't the recommended style to use a flexible array ([] instead of [0])?
See also https://lore.kernel.org/lkml/20200608213711.GA22271@embeddedor/.

Thanks,

Bart.