[PATCH 4/4] block: add IOC_PR_READ_RESERVATION ioctl

Stefan Hajnoczi
2025-11-26T16:36:21Z

Add a Persistent Reservations ioctl to read the current reservation.
This calls the pr_ops->read_reservation() 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_RESERVATION 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 | 28 ++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)

diff --git a/include/uapi/linux/pr.h b/include/uapi/linux/pr.h
index fcb74eab92c80..847f3051057af 100644
--- a/include/uapi/linux/pr.h
+++ b/include/uapi/linux/pr.h
@@ -62,6 +62,12 @@ struct pr_read_keys {
__u64 keys_ptr;
};

+struct pr_read_reservation {
+ __u64 key;
+ __u32 generation;
+ __u32 type;
+};
+
#define PR_FL_IGNORE_KEY (1 << 0) /* ignore existing key */

#define IOC_PR_REGISTER _IOW('p', 200, struct pr_registration)
@@ -71,5 +77,6 @@ struct pr_read_keys {
#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)
+#define IOC_PR_READ_RESERVATION _IOR('p', 207, struct pr_read_reservation)

#endif /* _UAPI_PR_H */
diff --git a/block/ioctl.c b/block/ioctl.c
index e87c424c15ae9..7e6d5e532d16b 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -472,6 +472,32 @@ static int blkdev_pr_read_keys(struct block_device *bdev, blk_mode_t mode,
return ret;
}

+static int blkdev_pr_read_reservation(struct block_device *bdev,
+ blk_mode_t mode, struct pr_read_reservation __user *arg)
+{
+ const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
+ struct pr_held_reservation rsv = {};
+ struct pr_read_reservation out = {};
+ int ret;
+
+ if (!blkdev_pr_allowed(bdev, mode))
+ return -EPERM;
+ if (!ops || !ops->pr_read_reservation)
+ return -EOPNOTSUPP;
+
+ ret = ops->pr_read_reservation(bdev, &rsv);
+ if (ret)
+ return ret;
+
+ out.key = rsv.key;
+ out.generation = rsv.generation;
+ out.type = rsv.type;
+
+ if (copy_to_user(arg, &out, sizeof(out)))
+ return -EFAULT;
+ return 0;
+}
+
static int blkdev_flushbuf(struct block_device *bdev, unsigned cmd,
unsigned long arg)
{
@@ -695,6 +721,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
return blkdev_pr_clear(bdev, mode, argp);
case IOC_PR_READ_KEYS:
return blkdev_pr_read_keys(bdev, mode, argp);
+ case IOC_PR_READ_RESERVATION:
+ return blkdev_pr_read_reservation(bdev, mode, argp);
default:
return blk_get_meta_cap(bdev, cmd, argp);
}
--
2.52.0