checkpoint.c

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		int drop_count = 0;
		int cleanup_ret, retry = 0;

		transaction = next_transaction;
		next_transaction = transaction->t_cpnext;
		jh = transaction->t_checkpoint_list;
		last_jh = jh->b_cpprev;
		next_jh = jh;
		do {
			jh = next_jh;
			next_jh = jh->b_cpnext;
			retry = __flush_buffer(journal, jh, bhs, &batch_count,
						&drop_count);
		} while (jh != last_jh && !retry);
		if (batch_count) {
			__flush_batch(bhs, &batch_count);
			goto repeat;
		}
		if (retry)
			goto repeat;
		/*
		 * We have walked the whole transaction list without
		 * finding anything to write to disk.  We had better be
		 * able to make some progress or we are in trouble. 
		 */
		cleanup_ret = __cleanup_transaction(journal, transaction);
		J_ASSERT(drop_count != 0 || cleanup_ret != 0);
		goto repeat;	/* __cleanup may have dropped lock */
	} while (transaction != last_transaction);

done:
	spin_unlock(&journal_datalist_lock);
	result = cleanup_journal_tail(journal);
	if (result < 0)
		return result;
	
	return 0;
}

/*
 * Check the list of checkpoint transactions for the journal to see if
 * we have already got rid of any since the last update of the log tail
 * in the journal superblock.  If so, we can instantly roll the
 * superblock forward to remove those transactions from the log.
 * 
 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 * 
 * Called with the journal lock held.
 *
 * This is the only part of the journaling code which really needs to be
 * aware of transaction aborts.  Checkpointing involves writing to the
 * main filesystem area rather than to the journal, so it can proceed
 * even in abort state, but we must not update the journal superblock if
 * we have an abort error outstanding.
 */

int cleanup_journal_tail(journal_t *journal)
{
	transaction_t * transaction;
	tid_t		first_tid;
	unsigned long	blocknr, freed;

	/* OK, work out the oldest transaction remaining in the log, and
	 * the log block it starts at. 
	 * 
	 * If the log is now empty, we need to work out which is the
	 * next transaction ID we will write, and where it will
	 * start. */

	/* j_checkpoint_transactions needs locking */
	spin_lock(&journal_datalist_lock);
	transaction = journal->j_checkpoint_transactions;
	if (transaction) {
		first_tid = transaction->t_tid;
		blocknr = transaction->t_log_start;
	} else if ((transaction = journal->j_committing_transaction) != NULL) {
		first_tid = transaction->t_tid;
		blocknr = transaction->t_log_start;
	} else if ((transaction = journal->j_running_transaction) != NULL) {
		first_tid = transaction->t_tid;
		blocknr = journal->j_head;
	} else {
		first_tid = journal->j_transaction_sequence;
		blocknr = journal->j_head;
	}
	spin_unlock(&journal_datalist_lock);
	J_ASSERT (blocknr != 0);

	/* If the oldest pinned transaction is at the tail of the log
           already then there's not much we can do right now. */
	if (journal->j_tail_sequence == first_tid)
		return 1;

	/* OK, update the superblock to recover the freed space.
	 * Physical blocks come first: have we wrapped beyond the end of
	 * the log?  */
	freed = blocknr - journal->j_tail;
	if (blocknr < journal->j_tail)
		freed = freed + journal->j_last - journal->j_first;

	jbd_debug(1,
		  "Cleaning journal tail from %d to %d (offset %lu), "
		  "freeing %lu\n",
		  journal->j_tail_sequence, first_tid, blocknr, freed);

	journal->j_free += freed;
	journal->j_tail_sequence = first_tid;
	journal->j_tail = blocknr;
	if (!(journal->j_flags & JFS_ABORT))
		journal_update_superblock(journal, 1);
	return 0;
}


/* Checkpoint list management */

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 *
 * Called with the journal locked.
 * Called with journal_datalist_lock held.
 * Returns number of bufers reaped (for debug)
 */

int __journal_clean_checkpoint_list(journal_t *journal)
{
	transaction_t *transaction, *last_transaction, *next_transaction;
	int ret = 0;

	transaction = journal->j_checkpoint_transactions;
	if (transaction == 0)
		goto out;

	last_transaction = transaction->t_cpprev;
	next_transaction = transaction;
	do {
		struct journal_head *jh;

		transaction = next_transaction;
		next_transaction = transaction->t_cpnext;
		jh = transaction->t_checkpoint_list;
		if (jh) {
			struct journal_head *last_jh = jh->b_cpprev;
			struct journal_head *next_jh = jh;
			do {
				jh = next_jh;
				next_jh = jh->b_cpnext;
				ret += __try_to_free_cp_buf(jh);
			} while (jh != last_jh);
		}
	} while (transaction != last_transaction);
out:
	return ret;
}

/* 
 * journal_remove_checkpoint: called after a buffer has been committed
 * to disk (either by being write-back flushed to disk, or being
 * committed to the log).
 *
 * We cannot safely clean a transaction out of the log until all of the
 * buffer updates committed in that transaction have safely been stored
 * elsewhere on disk.  To achieve this, all of the buffers in a
 * transaction need to be maintained on the transaction's checkpoint
 * list until they have been rewritten, at which point this function is
 * called to remove the buffer from the existing transaction's
 * checkpoint list.  
 *
 * This function is called with the journal locked.
 * This function is called with journal_datalist_lock held.
 */

void __journal_remove_checkpoint(struct journal_head *jh)
{
	transaction_t *transaction;
	journal_t *journal;

	JBUFFER_TRACE(jh, "entry");
	
	if ((transaction = jh->b_cp_transaction) == NULL) {
		JBUFFER_TRACE(jh, "not on transaction");
		goto out;
	}

	journal = transaction->t_journal;

	__buffer_unlink(jh);

	if (transaction->t_checkpoint_list != NULL)
		goto out;
	JBUFFER_TRACE(jh, "transaction has no more buffers");

	/* There is one special case to worry about: if we have just
           pulled the buffer off a committing transaction's forget list,
           then even if the checkpoint list is empty, the transaction
           obviously cannot be dropped! */

	if (transaction == journal->j_committing_transaction) {
		JBUFFER_TRACE(jh, "belongs to committing transaction");
		goto out;
	}

	/* OK, that was the last buffer for the transaction: we can now
	   safely remove this transaction from the log */

	__journal_drop_transaction(journal, transaction);

	/* Just in case anybody was waiting for more transactions to be
           checkpointed... */
	wake_up(&journal->j_wait_logspace);
out:
	JBUFFER_TRACE(jh, "exit");
}

void journal_remove_checkpoint(struct journal_head *jh)
{
	spin_lock(&journal_datalist_lock);
	__journal_remove_checkpoint(jh);
	spin_unlock(&journal_datalist_lock);
}

/*
 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 * list so that we know when it is safe to clean the transaction out of
 * the log.
 *
 * Called with the journal locked.
 * Called with journal_datalist_lock held.
 */
void __journal_insert_checkpoint(struct journal_head *jh, 
			       transaction_t *transaction)
{
	JBUFFER_TRACE(jh, "entry");
	J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jdirty(jh2bh(jh)));
	J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

	assert_spin_locked(&journal_datalist_lock);
	jh->b_cp_transaction = transaction;

	if (!transaction->t_checkpoint_list) {
		jh->b_cpnext = jh->b_cpprev = jh;
	} else {
		jh->b_cpnext = transaction->t_checkpoint_list;
		jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
		jh->b_cpprev->b_cpnext = jh;
		jh->b_cpnext->b_cpprev = jh;
	}
	transaction->t_checkpoint_list = jh;
}

void journal_insert_checkpoint(struct journal_head *jh, 
			       transaction_t *transaction)
{
	spin_lock(&journal_datalist_lock);
	__journal_insert_checkpoint(jh, transaction);
	spin_unlock(&journal_datalist_lock);
}

/*
 * We've finished with this transaction structure: adios...
 * 
 * The transaction must have no links except for the checkpoint by this
 * point.
 *
 * Called with the journal locked.
 * Called with journal_datalist_lock held.
 */

void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
	assert_spin_locked(&journal_datalist_lock);
	if (transaction->t_cpnext) {
		transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
		transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
		if (journal->j_checkpoint_transactions == transaction)
			journal->j_checkpoint_transactions =
				transaction->t_cpnext;
		if (journal->j_checkpoint_transactions == transaction)
			journal->j_checkpoint_transactions = NULL;
	}

	J_ASSERT (transaction->t_ilist == NULL);
	J_ASSERT (transaction->t_buffers == NULL);
	J_ASSERT (transaction->t_sync_datalist == NULL);
	J_ASSERT (transaction->t_async_datalist == NULL);
	J_ASSERT (transaction->t_forget == NULL);
	J_ASSERT (transaction->t_iobuf_list == NULL);
	J_ASSERT (transaction->t_shadow_list == NULL);
	J_ASSERT (transaction->t_log_list == NULL);
	J_ASSERT (transaction->t_checkpoint_list == NULL);
	J_ASSERT (transaction->t_updates == 0);
	
	J_ASSERT (transaction->t_journal->j_committing_transaction !=
					transaction);
	
	jbd_debug (1, "Dropping transaction %d, all done\n", 
		   transaction->t_tid);
	kfree (transaction);
}