drbd: protocol compatibility for maximum packet sizes

Two missing corner cases to the "maximum packet size" handshake.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

2 files changed, 17 insertions, 3 deletions

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 9ee44568dce3..9ae33a5bcf66 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -861,6 +861,7 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
         struct inode *inode, *inode2;
         struct lru_cache *resync_lru = NULL;
         union drbd_state ns, os;
+        unsigned int max_seg_s;
         int rv;
         int cp_discovered = 0;
         int logical_block_size;
@@ -1133,9 +1134,20 @@ static int drbd_nl_disk_conf(struct drbd_conf *mdev, struct drbd_nl_cfg_req *nlp
         mdev->read_cnt = 0;
         mdev->writ_cnt = 0;
 
-        drbd_setup_queue_param(mdev, mdev->state.conn == C_CONNECTED &&
-                               mdev->agreed_pro_version < 95 ?
-                               DRBD_MAX_SIZE_H80_PACKET : DRBD_MAX_SEGMENT_SIZE);
+        max_seg_s = DRBD_MAX_SEGMENT_SIZE;
+        if (mdev->state.conn == C_CONNECTED) {
+                /* We are Primary, Connected, and now attach a new local
+                 * backing store. We must not increase the user visible maximum
+                 * bio size on this device to something the peer may not be
+                 * able to handle. */
+                if (mdev->agreed_pro_version < 94)
+                        max_seg_s = queue_max_segment_size(mdev->rq_queue);
+                else if (mdev->agreed_pro_version == 94)
+                        max_seg_s = DRBD_MAX_SIZE_H80_PACKET;
+                /* else: drbd 8.3.9 and later, stay with default */
+        }
+
+        drbd_setup_queue_param(mdev, max_seg_s);
 
         /* If I am currently not R_PRIMARY,
          * but meta data primary indicator is set,
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 6b69b2f734dc..9da32ac62c22 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3088,6 +3088,8 @@ static int receive_sizes(struct drbd_conf *mdev, enum drbd_packets cmd, unsigned
 
                 if (mdev->agreed_pro_version < 94)
                         max_seg_s = be32_to_cpu(p->max_segment_size);
+                else if (mdev->agreed_pro_version == 94)
+                        max_seg_s = DRBD_MAX_SIZE_H80_PACKET;
                 else /* drbd 8.3.8 onwards */
                         max_seg_s = DRBD_MAX_SEGMENT_SIZE;