From: Josh Durgin <jdurgin@redhat.com>
Date: Wed, 25 Feb 2015 02:49:26 +0000 (-0800)
Subject: librbd: clarify md_lock usage
X-Git-Tag: v0.93~6^2~4
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=f4d8d16fbbb0a69c3bd8756e4096608294fccf9a;p=ceph.git

librbd: clarify md_lock usage

Signed-off-by: Josh Durgin <jdurgin@redhat.com>
---

diff --git a/src/librbd/ImageCtx.h b/src/librbd/ImageCtx.h
index cb1d64d737bb..deca81d11b7b 100644
--- a/src/librbd/ImageCtx.h
+++ b/src/librbd/ImageCtx.h
@@ -75,8 +75,14 @@ namespace librbd {
      */
     RWLock owner_lock; // protects exclusive lock leadership updates
     RWLock md_lock; // protects access to the mutable image metadata that
-                   // isn't guarded by other locks below
-                   // (flush_encountered, etc)
+                   // isn't guarded by other locks below, and blocks writes
+                   // when held exclusively, so snapshots can be consistent.
+                   // Fields guarded include:
+                   // flush_encountered
+                   // total_bytes_read
+                   // exclusive_locked
+                   // lock_tag
+                   // lockers
     Mutex cache_lock; // used as client_lock for the ObjectCacher
     RWLock snap_lock; // protects snapshot-related member variables, features, and flags
     RWLock parent_lock; // protects parent_md and parent