Re: [PATCH 3/4] block: add IOC_PR_READ_KEYS ioctl

Hannes Reinecke
2025-11-27T07:07:06Z

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@redhat.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@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich