[PATCH v3 01/19] block: Add PR callouts for read keys and reservation

Mike Christie
2022-10-26T23:20:14Z

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>
---
include/linux/pr.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)

diff --git a/include/linux/pr.h b/include/linux/pr.h
index 94ceec713afe..55c9ab7a202b 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 +26,18 @@ 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 is keys_len bytes. If there are more
+ * keys 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, u32 keys_len);
+ int (*pr_read_reservation)(struct block_device *bdev,
+ struct pr_held_reservation *rsv);
};

#endif /* LINUX_PR_H */
--
2.25.1