Message-id: <20080929201752.GN10950@webber.adilger.int>
Date:	Mon, 29 Sep 2008 14:17:52 -0600
From:	Andreas Dilger <adilger@....com>
To:	linux-ext4@...r.kernel.org
Cc:	"Theodore Ts'o" <tytso@....edu>
Subject: [PATCH] journal commit callback functions

Patch adds journal commit callbacks, and is what we are using for Lustre.
It is against 2.6.18, but applies with some small fuzz to newer kernels also.
The only position-sensitive part is the actual calling of the callbacks in
journal_commit_transaction(), right after the transaction is fully on disk.

======================= jbd-jcberr-2.6.18-vanilla.patch ===================
Implement a JBD per-transaction commit callback.  Users can attach arbitrary
callbacks to a journal handle, which are propagated to the transaction at
journal handle stop time.  The commit callbacks are run when the transaction
is finished commit, and will be passed a non-zero error code if there was
a commit error.

Signed-off-by: Andreas Dilger <adilger@....com>

Index: linux-2.6/include/linux/jbd.h
===================================================================
--- linux-2.6.orig/include/linux/jbd.h	2006-07-15 16:08:35.000000000 +0800
+++ linux-2.6/include/linux/jbd.h	2006-07-15 16:13:01.000000000 +0800
@@ -356,6 +356,28 @@ static inline void jbd_unlock_bh_journal
 	bit_spin_unlock(BH_JournalHead, &bh->b_state);
 }
 
+#define HAVE_JOURNAL_CALLBACK_STATUS
+/**
+ *   struct journal_callback - Base structure for callback information
+ *   @jcb_list: list information for other callbacks attached to the same handle
+ *   @jcb_func: Function to call with this callback structure
+ *
+ *   This struct is a 'seed' structure for a using with your own callback
+ *   structs. If you are using callbacks you must allocate one of these,
+ *   or another struct of your own definition which has this struct 
+ *   as it's first element and pass it to journal_callback_set().
+ *
+ *   This is used internally by jbd to maintain callback information, and
+ *   avoids the need to have 2 allocation/free per callback.
+ *
+ *   See journal_callback_set for more information.
+ **/
+struct journal_callback {
+	struct list_head jcb_list;		/* t_jcb_lock */
+	void (*jcb_func)(struct journal_callback *jcb, int error);
+	/* caller data goes here */
+};
+
 struct jbd_revoke_table_s;
 
 /**
@@ -364,6 +385,7 @@ struct jbd_revoke_table_s;
  * @h_transaction: Which compound transaction is this update a part of?
  * @h_buffer_credits: Number of remaining buffers we are allowed to dirty.
  * @h_ref: Reference count on this handle
+ * @h_jcb: List of application registered callbacks for this handle.
  * @h_err: Field for caller's use to track errors through large fs operations
  * @h_sync: flag for sync-on-close
  * @h_jdata: flag to force data journaling
@@ -389,6 +411,13 @@ struct handle_s 
 	/* operations */
 	int			h_err;
 
+	/*
+	 * List of application registered callbacks for this handle. The
+	 * function(s) will be called after the transaction that this handle is
+	 * part of has been committed to disk. [t_jcb_lock]
+	 */
+	struct list_head	h_jcb;
+
 	/* Flags [no locking] */
 	unsigned int	h_sync:		1;	/* sync-on-close */
 	unsigned int	h_jdata:	1;	/* force data journaling */
@@ -430,6 +459,8 @@ struct handle_s 
  *    j_state_lock
  *    ->j_list_lock			(journal_unmap_buffer)
  *
+ *    t_handle_lock
+ *    ->t_jcb_lock
  */
 
 struct transaction_s 
@@ -559,6 +590,15 @@ struct transaction_s 
 	 */
 	int t_handle_count;
 
+	/*
+	 * Protects the transaction callback list
+	 */
+	spinlock_t		t_jcb_lock;
+	/*
+	 * List of registered callback functions for this transaction.
+	 * Called when the transaction is committed. [t_jcb_lock]
+	 */
+	struct list_head	t_jcb;
 };
 
 /**
@@ -906,6 +946,10 @@ extern void	 journal_invalidatepage(jour
 extern int	 journal_try_to_free_buffers(journal_t *, struct page *, gfp_t);
 extern int	 journal_stop(handle_t *);
 extern int	 journal_flush (journal_t *);
+extern void	 journal_callback_set(handle_t *handle,
+				      void (*fn)(struct journal_callback *,int),
+				      struct journal_callback *jcb);
+
 extern void	 journal_lock_updates (journal_t *);
 extern void	 journal_unlock_updates (journal_t *);
 
Index: linux-2.6/fs/jbd/checkpoint.c
===================================================================
--- linux-2.6.orig/fs/jbd/checkpoint.c	2006-07-15 16:08:36.000000000 +0800
+++ linux-2.6/fs/jbd/checkpoint.c	2006-07-15 16:13:01.000000000 +0800
@@ -688,6 +688,7 @@ void __journal_drop_transaction(journal_
 	J_ASSERT(transaction->t_checkpoint_list == NULL);
 	J_ASSERT(transaction->t_checkpoint_io_list == NULL);
 	J_ASSERT(transaction->t_updates == 0);
+	J_ASSERT(list_empty(&transaction->t_jcb));
 	J_ASSERT(journal->j_committing_transaction != transaction);
 	J_ASSERT(journal->j_running_transaction != transaction);
 
Index: linux-2.6/fs/jbd/commit.c
===================================================================
--- linux-2.6.orig/fs/jbd/commit.c	2006-07-15 16:08:36.000000000 +0800
+++ linux-2.6/fs/jbd/commit.c	2006-07-15 16:13:01.000000000 +0800
@@ -708,6 +708,28 @@ wait_for_iobuf:
            transaction can be removed from any checkpoint list it was on
            before. */
 
+	/* Call any callbacks that had been registered for handles in this
+	 * transaction.  It is up to the callback to free any allocated
+	 * memory.
+	 *
+	 * Locking not strictly required, since this is the only process
+	 * touching this transaction anymore, but is done to keep code
+	 * checkers happy and has no contention in any case. */
+	spin_lock(&commit_transaction->t_jcb_lock);
+	if (!list_empty(&commit_transaction->t_jcb)) {
+		struct journal_callback *jcb, *n;
+		int error = is_journal_aborted(journal);
+
+		list_for_each_entry_safe(jcb, n, &commit_transaction->t_jcb,
+					 jcb_list) {
+			list_del_init(&jcb->jcb_list);
+			spin_unlock(&commit_transaction->t_jcb_lock);
+			jcb->jcb_func(jcb, error);
+			spin_lock(&commit_transaction->t_jcb_lock);
+		}
+	}
+	spin_unlock(&commit_transaction->t_jcb_lock);
+
 	jbd_debug(3, "JBD: commit phase 7\n");
 
 	J_ASSERT(commit_transaction->t_sync_datalist == NULL);
Index: linux-2.6/fs/jbd/journal.c
===================================================================
--- linux-2.6.orig/fs/jbd/journal.c	2006-07-15 16:08:36.000000000 +0800
+++ linux-2.6/fs/jbd/journal.c	2006-07-15 16:13:01.000000000 +0800
@@ -58,6 +58,7 @@ EXPORT_SYMBOL(journal_sync_buffer);
 #endif
 EXPORT_SYMBOL(journal_flush);
 EXPORT_SYMBOL(journal_revoke);
+EXPORT_SYMBOL(journal_callback_set);
 
 EXPORT_SYMBOL(journal_init_dev);
 EXPORT_SYMBOL(journal_init_inode);
Index: linux-2.6/fs/jbd/transaction.c
===================================================================
--- linux-2.6.orig/fs/jbd/transaction.c	2006-07-15 16:08:35.000000000 +0800
+++ linux-2.6/fs/jbd/transaction.c	2006-07-15 16:13:01.000000000 +0800
@@ -50,6 +50,8 @@ get_transaction(journal_t *journal, tran
 	transaction->t_state = T_RUNNING;
 	transaction->t_tid = journal->j_transaction_sequence++;
 	transaction->t_expires = jiffies + journal->j_commit_interval;
+	INIT_LIST_HEAD(&transaction->t_jcb);
+	spin_lock_init(&transaction->t_jcb_lock);
 	spin_lock_init(&transaction->t_handle_lock);
 
 	/* Set up the commit timer for the new transaction. */
@@ -241,6 +243,7 @@ static handle_t *new_handle(int nblocks)
 	memset(handle, 0, sizeof(*handle));
 	handle->h_buffer_credits = nblocks;
 	handle->h_ref = 1;
+	INIT_LIST_HEAD(&handle->h_jcb);
 
 	return handle;
 }
@@ -1291,6 +1294,35 @@ drop:
 }
 
 /**
+ * void journal_callback_set() -  Register a callback function for this handle.
+ * @handle: handle to attach the callback to.
+ * @func: function to callback.
+ * @jcb:  structure with additional information required by func() , and
+ *        some space for jbd internal information.
+ * 
+ * The function will be called when the transaction that this handle is
+ * part of has been committed to disk with the original callback data
+ * struct and the error status of the journal as parameters.  There is no
+ * guarantee of ordering between handles within a single transaction, nor
+ * between callbacks registered on the same handle.
+ *
+ * The caller is responsible for allocating the journal_callback struct.
+ * This is to allow the caller to add as much extra data to the callback
+ * as needed, but reduce the overhead of multiple allocations.  The caller
+ * allocated struct must start with a struct journal_callback at offset 0,
+ * and has the caller-specific data afterwards.
+ */
+void journal_callback_set(handle_t *handle,
+			  void (*func)(struct journal_callback *jcb, int error),
+			  struct journal_callback *jcb)
+{
+	jcb->jcb_func = func;
+	spin_lock(&handle->h_transaction->t_jcb_lock);
+	list_add_tail(&jcb->jcb_list, &handle->h_jcb);
+	spin_unlock(&handle->h_transaction->t_jcb_lock);
+}
+
+/**
  * int journal_stop() - complete a transaction
  * @handle: tranaction to complete.
  * 
@@ -1363,6 +1396,11 @@ int journal_stop(handle_t *handle)
 			wake_up(&journal->j_wait_transaction_locked);
 	}
 
+	/* Move callbacks from the handle to the transaction. */
+	spin_lock(&transaction->t_jcb_lock);
+	list_splice(&handle->h_jcb, &transaction->t_jcb);
+	spin_unlock(&transaction->t_jcb_lock);
+
 	/*
 	 * If the handle is marked SYNC, we need to set another commit
 	 * going!  We also want to force a commit if the current
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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