From 0b153daa6840258581deacb29d3d4c0f8d88f8b1 Mon Sep 17 00:00:00 2001
From: Joe Gorse <jhgorse@gmail.com>
Date: Thu, 25 Aug 2016 13:50:53 -0400
Subject: [PATCH 1/1] AFS callback story for reads and writes from multiple
 clients and one fileserver

---
 diagrams/afs-cb-story.mdwn | 52 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 diagrams/afs-cb-story.mdwn

diff --git a/diagrams/afs-cb-story.mdwn b/diagrams/afs-cb-story.mdwn
new file mode 100644
index 0000000..ba01d1f
--- /dev/null
+++ b/diagrams/afs-cb-story.mdwn
@@ -0,0 +1,52 @@
+[afs-cb-0][1]
+1. create file on *host d*
+ * data version (dv) = 1
+ * callback registration
+2. read on *hosts a,b,c*
+3. fetch-states
+4. add callback at fileserver
+
+![afs-cb-1][2]
+hello.c propagates to *hosts a,b,c* from fileserver. Callbacks are registered for a period of time. Callbacks notify a host if a change occurs.
+
+[afs-cb-2][3]
+host a modifies the file.
+1. open, write, close on *host a*
+2. store-data
+3. callbacks *b,c,d* are called
+ * "break" callbacks once called (i.e. remove them from the table once called)
+4. reply *dv=2* for *host a*
+ * incremented at the *fileserver*
+
+![afs-cb-3][4]
+read a stale file on *host c*.
+1. open, read on *host c*
+2. fetch-status
+ * returns *dv=2* > local cached *dv=1*
+3. fetch-data *dv=2* for *host c*
+ * registers callback for the file on *host c*
+
+[afs-cb-4][5]
+1. callbacks *a,c* expire.
+2. read file on *host c*
+3. fetch-status
+ * returns *dv=2* == local cached *dv*
+ * registers a new callback for the file on *host c* with *fileserver*
+4. new callback. cached data so local data is used.
+
+![afs-cb-5][6]
+a common failure mode: callback to host fails
+1. write, close on *host a*
+2. store-data
+3. callback (fails)
+4. store-data reply
+ * *fileserver* increments *dv=3*
+5. delayed callback (fails until it does not)
+6. callback expires (read fails)
+
+[1]: /diagrams/afs-cb-0.png "Create file"
+[2]: /diagrams/afs-cb-1.png "Replicate file"
+[3]: /diagrams/afs-cb-2.png "Modify file"
+[4]: /diagrams/afs-cb-3.png "Read stale file"
+[5]: /diagrams/afs-cb-4.png "Callback expires"
+[6]: /diagrams/afs-cb-5.png "Callback failure"
-- 
1.9.4