On Sep 14, 2008 19:31 -0700, Andreas Dilger wrote:
> We had a much more flexible journal commit notification mechanism. The
> caller would register a callback with the journal layer that contained
> a caller-private callback function and callback data. This avoided
> exposing the journal transaction IDs outside of the filesystem, and the
> caller could use any identifier desired.
>
> There was also no limit on the number/type of callbacks registered with
> the filesystem. The basic data structure was a linked list of callbacks
> registered on the transaction:
>
> struct journal_callback {
> struct list_head jcb_list;
> void (*jcb_func)(struct journal_callback *jcb, int error);
> /* caller data goes here */
> };
>
> and in journal_commit_transaction() the callbacks are called:
>
> list_for_each_entry_safe(jcb, n, &commit_transaction->t_jcb,
> jcb_list) {
> list_del_init(&jcb->jcb_list);
> jcb->jcb_func(jcb, error);
> }
Here is the patch (against 2.6.18 kernels, but I don't think anything has
changed in this area in a long time):
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 +356,27 @@ 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.
+ *
+ * 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 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 +708,21 @@ 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. No locking is required, since this is the only process
+ * that is processing this transaction anymore. */
+ 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);
+ jcb->jcb_func(jcb, error);
+ }
+ }
+
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 +1294,36 @@ 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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