linux-kernel - Re: [PATCH 3/4] block: add IOC_PR_READ

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Message-ID: <cfd7cace-563b-4fcb-9415-72ac0eb3e811@suse.de>
Date: Thu, 27 Nov 2025 08:07:04 +0100
From: Hannes Reinecke <hare@...e.de>
To: Stefan Hajnoczi <stefanha@...hat.com>, linux-block@...r.kernel.org
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>,
 linux-kernel@...r.kernel.org,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 Mike Christie <michael.christie@...cle.com>, Jens Axboe <axboe@...nel.dk>,
 linux-nvme@...ts.infradead.org, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>, linux-scsi@...r.kernel.org,
 Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 3/4] block: add IOC_PR_READ_KEYS ioctl

On 11/26/25 17:35, Stefan Hajnoczi wrote:
> Add a Persistent Reservations ioctl to read the list of currently
> registered reservation keys. This calls the pr_ops->read_keys() function
> that was previously added in commit c787f1baa503 ("block: Add PR
> callouts for read keys and reservation") but was only used by the
> in-kernel SCSI target so far.
> 
> The IOC_PR_READ_KEYS ioctl is necessary so that userspace applications
> that rely on Persistent Reservations ioctls have a way of inspecting the
> current state. Cluster managers and validation tests need this
> functionality.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
> ---
>   include/uapi/linux/pr.h |  7 ++++++
>   block/ioctl.c           | 51 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 58 insertions(+)
> 
> diff --git a/include/uapi/linux/pr.h b/include/uapi/linux/pr.h
> index d8126415966f3..fcb74eab92c80 100644
> --- a/include/uapi/linux/pr.h
> +++ b/include/uapi/linux/pr.h
> @@ -56,6 +56,12 @@ struct pr_clear {
>   	__u32	__pad;
>   };
>   
> +struct pr_read_keys {
> +	__u32	generation;
> +	__u32	num_keys;
> +	__u64	keys_ptr;
> +};
> +
>   #define PR_FL_IGNORE_KEY	(1 << 0)	/* ignore existing key */
>   
>   #define IOC_PR_REGISTER		_IOW('p', 200, struct pr_registration)
> @@ -64,5 +70,6 @@ struct pr_clear {
>   #define IOC_PR_PREEMPT		_IOW('p', 203, struct pr_preempt)
>   #define IOC_PR_PREEMPT_ABORT	_IOW('p', 204, struct pr_preempt)
>   #define IOC_PR_CLEAR		_IOW('p', 205, struct pr_clear)
> +#define IOC_PR_READ_KEYS	_IOWR('p', 206, struct pr_read_keys)
>   
>   #endif /* _UAPI_PR_H */
> diff --git a/block/ioctl.c b/block/ioctl.c
> index d7489a56b33c3..e87c424c15ae9 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -1,5 +1,6 @@
>   // SPDX-License-Identifier: GPL-2.0
>   #include <linux/capability.h>
> +#include <linux/cleanup.h>
>   #include <linux/compat.h>
>   #include <linux/blkdev.h>
>   #include <linux/export.h>
> @@ -423,6 +424,54 @@ static int blkdev_pr_clear(struct block_device *bdev, blk_mode_t mode,
>   	return ops->pr_clear(bdev, c.key);
>   }
>   
> +static int blkdev_pr_read_keys(struct block_device *bdev, blk_mode_t mode,
> +		struct pr_read_keys __user *arg)
> +{
> +	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
> +	struct pr_keys *keys_info __free(kfree) = NULL;
> +	struct pr_read_keys inout;
> +	int ret;
> +
> +	if (!blkdev_pr_allowed(bdev, mode))
> +		return -EPERM;
> +	if (!ops || !ops->pr_read_keys)
> +		return -EOPNOTSUPP;
> +
> +	if (copy_from_user(&inout, arg, sizeof(inout)))
> +		return -EFAULT;
> +
> +	if (inout.num_keys > -sizeof(*keys_info) / sizeof(keys_info->keys[0]))
> +		return -EINVAL;
> +

0-sizeof()? What's that supposed to achieve? Plus inout.numkeys is 
unsigned (as the kbuild robot indicated).

> +	size_t keys_info_len = struct_size(keys_info, keys, inout.num_keys);
> +
> +	keys_info = kzalloc(keys_info_len, GFP_KERNEL);
> +	if (!keys_info)
> +		return -ENOMEM;
> +
> +	keys_info->num_keys = inout.num_keys;
> +
> +	ret = ops->pr_read_keys(bdev, keys_info);
> +	if (ret)
> +		return ret;
> +
> +	/* Copy out individual keys */
> +	u64 __user *keys_ptr = u64_to_user_ptr(inout.keys_ptr);
> +	u32 num_copy_keys = min(inout.num_keys, keys_info->num_keys);
> +	size_t keys_copy_len = num_copy_keys * sizeof(keys_info->keys[0]);

We just had the discussion about variable declarations on the ksummit 
lists; I really would prefer to have all declarations at the start of 
the scope (read: at the start of the function here).

> +
> +	if (copy_to_user(keys_ptr, keys_info->keys, keys_copy_len))
> +		return -EFAULT;
> +
> +	/* Copy out the arg struct */
> +	inout.generation = keys_info->generation;
> +	inout.num_keys = keys_info->num_keys;
> +
> +	if (copy_to_user(arg, &inout, sizeof(inout)))
> +		return -EFAULT;
> +	return ret;
> +}
> +
>   static int blkdev_flushbuf(struct block_device *bdev, unsigned cmd,
>   		unsigned long arg)
>   {
> @@ -644,6 +693,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
>   		return blkdev_pr_preempt(bdev, mode, argp, true);
>   	case IOC_PR_CLEAR:
>   		return blkdev_pr_clear(bdev, mode, argp);
> +	case IOC_PR_READ_KEYS:
> +		return blkdev_pr_read_keys(bdev, mode, argp);
>   	default:
>   		return blk_get_meta_cap(bdev, cmd, argp);
>   	Cheers,Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich