From 3ffb892cbb0b96a57595b9962d018191c5b3d5af Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Mon, 14 Sep 2009 10:23:25 -0700
Subject: [PATCH] Update filesystem locking rules (in progress).

---
 bluesky/inode.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/bluesky/inode.c b/bluesky/inode.c
index 4d07a52..8faafa4 100644
--- a/bluesky/inode.c
+++ b/bluesky/inode.c
@@ -28,7 +28,7 @@ int64_t bluesky_get_current_time()
 
 /* Update an inode to indicate that a modification was made.  This increases
  * the change counter, updates the ctime to the current time, and optionally
- * updates the mtime. */
+ * updates the mtime.  inode must already be locked. */
 void bluesky_inode_update_ctime(BlueSkyInode *inode, gboolean update_mtime)
 {
     int64_t now = bluesky_get_current_time();
@@ -87,15 +87,13 @@ void bluesky_inode_unref(BlueSkyInode *inode)
 }
 
 /* Allocate a fresh inode number which has not been used before within a
- * filesystem. */
+ * filesystem.  fs must already be locked. */
 uint64_t bluesky_fs_alloc_inode(BlueSkyFS *fs)
 {
     uint64_t inum;
 
-    g_mutex_lock(fs->lock);
     inum = fs->next_inum;
     fs->next_inum++;
-    g_mutex_unlock(fs->lock);
 
     return inum;
 }
@@ -132,31 +130,34 @@ BlueSkyInode *bluesky_new_inode(uint64_t inum, BlueSkyFS *fs,
 
 /* Retrieve an inode from the filesystem.  Eventually this will be a cache and
  * so we might need to go fetch the inode from elsewhere; for now all
- * filesystem state is stored here. */
+ * filesystem state is stored here.  inode is returned locked with a reference
+ * held. */
 BlueSkyInode *bluesky_get_inode(BlueSkyFS *fs, uint64_t inum)
 {
     BlueSkyInode *inode = NULL;
 
     g_mutex_lock(fs->lock);
     inode = (BlueSkyInode *)g_hash_table_lookup(fs->inodes, &inum);
-    g_mutex_unlock(fs->lock);
 
     if (inode == NULL) {
         bluesky_inode_fetch(fs, inum);
-        g_mutex_lock(fs->lock);
         inode = (BlueSkyInode *)g_hash_table_lookup(fs->inodes, &inum);
-        g_mutex_unlock(fs->lock);
     }
 
+    if (inode != NULL) {
+        g_mutex_lock(inode->lock);
+        bluesky_inode_ref(inode);
+    }
+
+    g_mutex_unlock(fs->lock);
+
     return inode;
 }
 
-/* Insert an inode into the filesystem inode cache. */
+/* Insert an inode into the filesystem inode cache.  fs should be locked. */
 void bluesky_insert_inode(BlueSkyFS *fs, BlueSkyInode *inode)
 {
-    g_mutex_lock(fs->lock);
     g_hash_table_insert(fs->inodes, &inode->inum, inode);
-    g_mutex_unlock(fs->lock);
 }
 
 /* Synchronize an inode to stable storage. */
-- 
2.20.1