[PATCH v5 01/18] block: Add PR callouts for read keys and reservation

From: Mike Christie <michael.christie@oracle.com>
To: bvanassche@acm.org, hch@lst.de, martin.petersen@oracle.com,
	linux-scsi@vger.kernel.org,
	james.bottomley@hansenpartnership.com,
	linux-block@vger.kernel.org, dm-devel@redhat.com,
	snitzer@kernel.org, axboe@kernel.dk,
	linux-nvme@lists.infradead.org, chaitanyak@nvidia.com,
	kbusch@kernel.org, target-devel@vger.kernel.org
Cc: Mike Christie <michael.christie@oracle.com>,
	Chaitanya Kulkarni <kch@nvidia.com>
Subject: [PATCH v5 01/18] block: Add PR callouts for read keys and reservation
Date: Fri, 24 Mar 2023 13:17:24 -0500	[thread overview]
Message-ID: <20230324181741.13908-2-michael.christie@oracle.com> (raw)
In-Reply-To: <20230324181741.13908-1-michael.christie@oracle.com>

Add callouts for reading keys and reservations. This allows LIO to support
the READ_KEYS and READ_RESERVATION commands and will allow dm-multipath
to optimize it's error handling so it can check if it's getting an error
because there's an existing reservation or if we need to retry different
paths.

Note: This only initially adds the struct definitions in the kernel as I'm
not sure if we wanted to export the interface to userspace yet. read_keys
and read_reservation are exactly what dm-multipath and LIO need, but for a
userspace interface we may want something like SCSI's READ_FULL_STATUS and
NVMe's report reservation commands. Those are overkill for dm/LIO and
READ_FULL_STATUS is sometimes broken for SCSI devices.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/pr.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/linux/pr.h b/include/linux/pr.h
index 94ceec713afe..3003daec28a5 100644
--- a/include/linux/pr.h
+++ b/include/linux/pr.h
@@ -4,6 +4,18 @@
 
 #include <uapi/linux/pr.h>
 
+struct pr_keys {
+	u32	generation;
+	u32	num_keys;
+	u64	keys[];
+};
+
+struct pr_held_reservation {
+	u64		key;
+	u32		generation;
+	enum pr_type	type;
+};
+
 struct pr_ops {
 	int (*pr_register)(struct block_device *bdev, u64 old_key, u64 new_key,
 			u32 flags);
@@ -14,6 +26,19 @@ struct pr_ops {
 	int (*pr_preempt)(struct block_device *bdev, u64 old_key, u64 new_key,
 			enum pr_type type, bool abort);
 	int (*pr_clear)(struct block_device *bdev, u64 key);
+	/*
+	 * pr_read_keys - Read the registered keys and return them in the
+	 * pr_keys->keys array. The keys array will have been allocated at the
+	 * end of the pr_keys struct, and pr_keys->num_keys must be set to the
+	 * number of keys the array can hold. If there are more than can fit
+	 * in the array, success will still be returned and pr_keys->num_keys
+	 * will reflect the total number of keys the device contains, so the
+	 * caller can retry with a larger array.
+	 */
+	int (*pr_read_keys)(struct block_device *bdev,
+			struct pr_keys *keys_info);
+	int (*pr_read_reservation)(struct block_device *bdev,
+			struct pr_held_reservation *rsv);
 };
 
 #endif /* LINUX_PR_H */
-- 
2.25.1

