From 25d6576a52231833911d72b048f86111f6c22106 Mon Sep 17 00:00:00 2001
From: Greg Farnum <gregf@hq.newdream.net>
Date: Thu, 18 Nov 2010 11:56:04 -0800
Subject: [PATCH] Journaler: add new reread_head function and state.

This is to facilitate the forthcoming up_shadow MDS state.

Signed-off-by: Greg Farnum <gregf@hq.newdream.net>
---
 src/osdc/Journaler.cc | 43 ++++++++++++++++++++++++++++++++++++++++++-
 src/osdc/Journaler.h  |  3 +++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/osdc/Journaler.cc b/src/osdc/Journaler.cc
index 8ecda4f2c7ada..5cfe282ad7925 100644
--- a/src/osdc/Journaler.cc
+++ b/src/osdc/Journaler.cc
@@ -86,6 +86,7 @@ public:
 
 void Journaler::recover(Context *onread) 
 {
+  dout(1) << "recover start" << dendl;
   assert(state != STATE_ACTIVE);
 
   if (onread)
@@ -99,10 +100,50 @@ void Journaler::recover(Context *onread)
   dout(1) << "read_head" << dendl;
   state = STATE_READHEAD;
   C_ReadHead *fin = new C_ReadHead(this);
+  read_head(fin, &fin->bl);
+}
+
+void Journaler::read_head(Context *on_finish, bufferlist *bl)
+{
+  assert(state == STATE_READHEAD || state == STATE_REREADHEAD);
 
   object_t oid = file_object_t(ino, 0);
   object_locator_t oloc(pg_pool);
-  objecter->read_full(oid, oloc, CEPH_NOSNAP, &fin->bl, 0, fin);
+  objecter->read_full(oid, oloc, CEPH_NOSNAP, bl, 0, on_finish);
+}
+
+/**
+ * Re-read the head from disk, and set the write_pos, expire_pos, trimmed_pos
+ * from the on-disk header. This switches the state to STATE_REREADHEAD for
+ * the duration, and you shouldn't start a re-read while other operations are
+ * in-flight, nor start other operations while a re-read is in progress.
+ * Also, don't call this until the Journaler has finished its recovery and has
+ * gone STATE_ACTIVE!
+ */
+void Journaler::reread_head()
+{
+  dout(10) << "reread_head" << dendl;
+  assert(state == STATE_ACTIVE);
+
+  Mutex lock("Journaler::reread_head");
+  Cond cond;
+  bool done = false;
+  bufferlist bl;
+  state = STATE_REREADHEAD;
+  read_head(new C_SafeCond(&lock, &cond, &done), &bl);
+  while (!done) cond.Wait(lock);
+
+  //read on-disk header into
+  assert (bl.length());
+
+  // unpack header
+  Header h;
+  bufferlist::iterator p = bl.begin();
+  ::decode(h, p);
+  write_pos = h.write_pos;
+  expire_pos = h.expire_pos;
+  trimmed_pos = h.trimmed_pos;
+  state = STATE_ACTIVE;
 }
 
 void Journaler::_finish_read_head(int r, bufferlist& bl)
diff --git a/src/osdc/Journaler.h b/src/osdc/Journaler.h
index 705de92641d09..30a973f875ec3 100644
--- a/src/osdc/Journaler.h
+++ b/src/osdc/Journaler.h
@@ -129,6 +129,7 @@ public:
   static const int STATE_READHEAD = 1;
   static const int STATE_PROBING = 2;
   static const int STATE_ACTIVE = 2;
+  static const int STATE_REREADHEAD = 3;
 
   int state;
   int error;
@@ -232,6 +233,8 @@ public:
    */
   void create(ceph_file_layout *layout);
   void recover(Context *onfinish);
+  void read_head(Context *on_finish, bufferlist *bl);
+  void reread_head();
   void write_head(Context *onsave=0);
 
   void set_layout(ceph_file_layout *l);
-- 
2.39.5