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

-----Original Message-----
From: Bart Van Assche <bvanassche@acm.org>
Sent: Monday, 29 June 2020 03.36
To: Matias Bjorling <redacted>; axboe@kernel.dk;
kbusch@kernel.org; hch@lst.de; sagi@grimberg.me;
martin.petersen@oracle.com; Damien Le Moal [off-list ref];
Niklas Cassel [off-list ref]; Hans Holmberg
[off-list ref]
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

On 2020-06-28 16:01, Matias Bjørling wrote:

quoted

+	/* 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?

One can't be too careful these days, heh. I'll fix it up. Thanks!

quoted

+	/* no flags is currently supported */

                    ^^
                    are?

quoted

+	/* 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()?

quoted

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);
}

quoted

+/**
+ * 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/ (local).

Thanks,

Bart.