From 6c509e7a6e90c2e8e55613e29cb08dc2674e30de Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Tue, 23 Mar 2021 16:15:43 +0100
Subject: [KERNEL] Set fake low RTT after manual server switch

This avoids automatically switching back right after adding
and switching to a server.
---
 src/kernel/blk.c        | 7 +++++++
 src/kernel/dnbd3_main.c | 1 +
 2 files changed, 8 insertions(+)

diff --git a/src/kernel/blk.c b/src/kernel/blk.c
index 661bc2e..90e9b34 100644
--- a/src/kernel/blk.c
+++ b/src/kernel/blk.c
@@ -247,6 +247,13 @@ static int dnbd3_blk_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
 							/* switching didn't work but we are back to the old server */
 							result = -EAGAIN;
 						}
+					} else {
+						/* switch succeeded, fake very low RTT so we don't switch away again soon */
+						mutex_lock(&dev->alt_servers_lock);
+						if (is_same_server(alt_server, &new_server)) {
+							alt_server->rtts[0] = alt_server->rtts[1] = alt_server->rtts[2] = alt_server->rtts[3] = 4;
+						}
+						mutex_unlock(&dev->alt_servers_lock);
 					}
 				} else {
 					/* specified server is already working, so do not switch */
diff --git a/src/kernel/dnbd3_main.c b/src/kernel/dnbd3_main.c
index 17d553e..7a3b1d5 100644
--- a/src/kernel/dnbd3_main.c
+++ b/src/kernel/dnbd3_main.c
@@ -66,6 +66,7 @@ static inline dnbd3_server_t *get_free_alt_server(dnbd3_device_t *const dev)
 /**
  * Returns pointer to existing entry in alt_servers that matches the given
  * alt server, or NULL if not found.
+ * The caller has to hold dev->alt_servers_lock.
  */
 dnbd3_server_t *get_existing_server(const dnbd3_host_t *const newserver, dnbd3_device_t *const dev)
 {
-- 
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