transaction.c

嵌入式系统设计与实例开发实验教材二源码 多线程应用程序设计 串行端口程序设计 AD接口实验 CAN总线通信实验 GPS通信实验 Linux内核移植与编译实验 IC卡读写实验 SD驱动使

	/*
	 * akpm: I added this.  ext3_alloc_branch can pick up new indirect
	 * blocks which contain freed but then revoked metadata.  We need
	 * to cancel the revoke in case we end up freeing it yet again
	 * and the reallocating as data - this would cause a second revoke,
	 * which hits an assertion error.
	 */
	JBUFFER_TRACE(jh, "cancelling revoke");
	journal_cancel_revoke(handle, jh);
	journal_unlock_journal_head(jh);
out:
	unlock_journal(journal);
	return err;
}



/*
 * journal_get_undo_access: Notify intent to modify metadata with non-
 * rewindable consequences
 *
 * Sometimes there is a need to distinguish between metadata which has
 * been committed to disk and that which has not.  The ext3fs code uses
 * this for freeing and allocating space: we have to make sure that we
 * do not reuse freed space until the deallocation has been committed,
 * since if we overwrote that space we would make the delete
 * un-rewindable in case of a crash.
 * 
 * To deal with that, journal_get_undo_access requests write access to a
 * buffer for parts of non-rewindable operations such as delete
 * operations on the bitmaps.  The journaling code must keep a copy of
 * the buffer's contents prior to the undo_access call until such time
 * as we know that the buffer has definitely been committed to disk.
 * 
 * We never need to know which transaction the committed data is part
 * of: buffers touched here are guaranteed to be dirtied later and so
 * will be committed to a new transaction in due course, at which point
 * we can discard the old committed data pointer.
 *
 * Returns error number or 0 on success.  
 */

int journal_get_undo_access (handle_t *handle, struct buffer_head *bh)
{
	journal_t *journal = handle->h_transaction->t_journal;
	int err;
	struct journal_head *jh = journal_add_journal_head(bh);

	JBUFFER_TRACE(jh, "entry");
	lock_journal(journal);

	/* Do this first --- it can drop the journal lock, so we want to
	 * make sure that obtaining the committed_data is done
	 * atomically wrt. completion of any outstanding commits. */
	err = do_get_write_access (handle, jh, 1);
	if (err)
		goto out;
	
	if (!jh->b_committed_data) {
		/* Copy out the current buffer contents into the
		 * preserved, committed copy. */
		JBUFFER_TRACE(jh, "generate b_committed data");
		jh->b_committed_data = jbd_kmalloc(jh2bh(jh)->b_size, 
						   GFP_NOFS);
		if (!jh->b_committed_data) {
			printk(KERN_EMERG __FUNCTION__
				": No memory for committed data!\n");
			err = -ENOMEM;
			goto out;
		}
		
		memcpy (jh->b_committed_data, jh2bh(jh)->b_data,
				jh2bh(jh)->b_size);
	}

out:
	if (!err)
		J_ASSERT_JH(jh, jh->b_committed_data);
	journal_unlock_journal_head(jh);
	unlock_journal(journal);
	return err;
}

/* 
 * journal_dirty_data: mark a buffer as containing dirty data which
 * needs to be flushed before we can commit the current transaction.  
 *
 * The buffer is placed on the transaction's data list and is marked as
 * belonging to the transaction.
 *
 * If `async' is set then the writebask will be initiated by the caller
 * using submit_bh -> end_buffer_io_async.  We put the buffer onto
 * t_async_datalist.
 * 
 * Returns error number or 0 on success.  
 *
 * journal_dirty_data() can be called via page_launder->ext3_writepage
 * by kswapd.  So it cannot block.  Happily, there's nothing here
 * which needs lock_journal if `async' is set.
 *
 * When the buffer is on the current transaction we freely move it
 * between BJ_AsyncData and BJ_SyncData according to who tried to
 * change its state last.
 */

int journal_dirty_data (handle_t *handle, struct buffer_head *bh, int async)
{
	journal_t *journal = handle->h_transaction->t_journal;
	int need_brelse = 0;
	int wanted_jlist = async ? BJ_AsyncData : BJ_SyncData;
	struct journal_head *jh;

	if (is_handle_aborted(handle))
		return 0;
	
	jh = journal_add_journal_head(bh);
	JBUFFER_TRACE(jh, "entry");

	/*
	 * The buffer could *already* be dirty.  Writeout can start
	 * at any time.
	 */
	jbd_debug(4, "jh: %p, tid:%d\n", jh, handle->h_transaction->t_tid);

	/*
	 * What if the buffer is already part of a running transaction?
	 * 
	 * There are two cases:
	 * 1) It is part of the current running transaction.  Refile it,
	 *    just in case we have allocated it as metadata, deallocated
	 *    it, then reallocated it as data. 
	 * 2) It is part of the previous, still-committing transaction.
	 *    If all we want to do is to guarantee that the buffer will be
	 *    written to disk before this new transaction commits, then
	 *    being sure that the *previous* transaction has this same 
	 *    property is sufficient for us!  Just leave it on its old
	 *    transaction.
	 *
	 * In case (2), the buffer must not already exist as metadata
	 * --- that would violate write ordering (a transaction is free
	 * to write its data at any point, even before the previous
	 * committing transaction has committed).  The caller must
	 * never, ever allow this to happen: there's nothing we can do
	 * about it in this layer.
	 */
	spin_lock(&journal_datalist_lock);
	if (jh->b_transaction) {
		JBUFFER_TRACE(jh, "has transaction");
		if (jh->b_transaction != handle->h_transaction) {
			JBUFFER_TRACE(jh, "belongs to older transaction");
			J_ASSERT_JH(jh, jh->b_transaction ==
					journal->j_committing_transaction);

			/* @@@ IS THIS TRUE  ? */
			/*
			 * Not any more.  Scenario: someone does a write()
			 * in data=journal mode.  The buffer's transaction has
			 * moved into commit.  Then someone does another
			 * write() to the file.  We do the frozen data copyout
			 * and set b_next_transaction to point to j_running_t.
			 * And while we're in that state, someone does a
			 * writepage() in an attempt to pageout the same area
			 * of the file via a shared mapping.  At present that
			 * calls journal_dirty_data(), and we get right here.
			 * It may be too late to journal the data.  Simply
			 * falling through to the next test will suffice: the
			 * data will be dirty and wil be checkpointed.  The
			 * ordering comments in the next comment block still
			 * apply.
			 */
			//J_ASSERT_JH(jh, jh->b_next_transaction == NULL);

			/*
			 * If we're journalling data, and this buffer was
			 * subject to a write(), it could be metadata, forget
			 * or shadow against the committing transaction.  Now,
			 * someone has dirtied the same darn page via a mapping
			 * and it is being writepage()'d.
			 * We *could* just steal the page from commit, with some
			 * fancy locking there.  Instead, we just skip it -
			 * don't tie the page's buffers to the new transaction
			 * at all.
			 * Implication: if we crash before the writepage() data
			 * is written into the filesystem, recovery will replay
			 * the write() data.
			 */
			if (jh->b_jlist != BJ_None &&
					jh->b_jlist != BJ_SyncData &&
					jh->b_jlist != BJ_AsyncData) {
				JBUFFER_TRACE(jh, "Not stealing");
				goto no_journal;
			}

			/*
			 * This buffer may be undergoing writeout in commit.  We
			 * can't return from here and let the caller dirty it
			 * again because that can cause the write-out loop in
			 * commit to never terminate.
			 */
			if (!async && buffer_dirty(bh)) {
				atomic_inc(&bh->b_count);
				spin_unlock(&journal_datalist_lock);
				need_brelse = 1;
				ll_rw_block(WRITE, 1, &bh);
				wait_on_buffer(bh);
				spin_lock(&journal_datalist_lock);
				/* The buffer may become locked again at any
				   time if it is redirtied */
			}

			/* journal_clean_data_list() may have got there first */
			if (jh->b_transaction != NULL) {
				JBUFFER_TRACE(jh, "unfile from commit");
				__journal_unfile_buffer(jh);
				jh->b_transaction = NULL;
			}
			/* The buffer will be refiled below */

		}
		/*
		 * Special case --- the buffer might actually have been
		 * allocated and then immediately deallocated in the previous,
		 * committing transaction, so might still be left on that
		 * transaction's metadata lists.
		 */
		if (jh->b_jlist != wanted_jlist) {
			JBUFFER_TRACE(jh, "not on correct data list: unfile");
			J_ASSERT_JH(jh, jh->b_jlist != BJ_Shadow);
			__journal_unfile_buffer(jh);
			jh->b_transaction = NULL;
			JBUFFER_TRACE(jh, "file as data");
			__journal_file_buffer(jh, handle->h_transaction,
						wanted_jlist);
		}
	} else {
		JBUFFER_TRACE(jh, "not on a transaction");
		__journal_file_buffer(jh, handle->h_transaction, wanted_jlist);
	}
no_journal:
	spin_unlock(&journal_datalist_lock);
	if (need_brelse) {
		BUFFER_TRACE(bh, "brelse");
		__brelse(bh);
	}
	JBUFFER_TRACE(jh, "exit");
	journal_unlock_journal_head(jh);
	return 0;
}

/* 
 * journal_dirty_metadata: mark a buffer as containing dirty metadata
 * which needs to be journaled as part of the current transaction.
 *
 * The buffer is placed on the transaction's metadata list and is marked
 * as belonging to the transaction.  
 *
 * Special care needs to be taken if the buffer already belongs to the
 * current committing transaction (in which case we should have frozen
 * data present for that commit).  In that case, we don't relink the
 * buffer: that only gets done when the old transaction finally
 * completes its commit.
 * 
 * Returns error number or 0 on success.  
 */

int journal_dirty_metadata (handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal = transaction->t_journal;
	struct journal_head *jh = bh2jh(bh);

	jbd_debug(5, "journal_head %p\n", jh);
	JBUFFER_TRACE(jh, "entry");
	lock_journal(journal);
	if (is_handle_aborted(handle))
		goto out_unlock;
	
	spin_lock(&journal_datalist_lock);
	set_bit(BH_JBDDirty, &bh->b_state);
	set_buffer_flushtime(bh);

	J_ASSERT_JH(jh, jh->b_transaction != NULL);
	
	/* 
	 * Metadata already on the current transaction list doesn't
	 * need to be filed.  Metadata on another transaction's list must
	 * be committing, and will be refiled once the commit completes:
	 * leave it alone for now. 
	 */

	if (jh->b_transaction != transaction) {
		JBUFFER_TRACE(jh, "already on other transaction");
		J_ASSERT_JH(jh, jh->b_transaction ==
					journal->j_committing_transaction);
		J_ASSERT_JH(jh, jh->b_next_transaction == transaction);
		/* And this case is illegal: we can't reuse another
		 * transaction's data buffer, ever. */
		/* FIXME: writepage() should be journalled */
		J_ASSERT_JH(jh, jh->b_jlist != BJ_SyncData);
		goto done_locked;
	}

	/* That test should have eliminated the following case: */
	J_ASSERT_JH(jh, jh->b_frozen_data == 0);

	JBUFFER_TRACE(jh, "file as BJ_Metadata");
	__journal_file_buffer(jh, handle->h_transaction, BJ_Metadata);

done_locked:
	spin_unlock(&journal_datalist_lock);
	JBUFFER_TRACE(jh, "exit");
out_unlock:
	unlock_journal(journal);
	return 0;
}

#if 0
/* 
 * journal_release_buffer: undo a get_write_access without any buffer
 * updates, if the update decided in the end that it didn't need access.
 *
 * journal_get_write_access() can block, so it is quite possible for a
 * journaling component to decide after the write access is returned
 * that global state has changed and the update is no longer required.  */

void journal_release_buffer (handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal = transaction->t_journal;
	struct journal_head *jh = bh2jh(bh);

	lock_journal(journal);
	JBUFFER_TRACE(jh, "entry");

	/* If the buffer is reserved but not modified by this
	 * transaction, then it is safe to release it.  In all other
	 * cases, just leave the buffer as it is. */

	spin_lock(&journal_datalist_lock);
	if (jh->b_jlist == BJ_Reserved && jh->b_transaction == transaction &&
	    !buffer_jdirty(jh2bh(jh))) {
		JBUFFER_TRACE(jh, "unused: refiling it");
		handle->h_buffer_credits++;
		__journal_refile_buffer(jh);
	}
	spin_unlock(&journal_datalist_lock);

	JBUFFER_TRACE(jh, "exit");
	unlock_journal(journal);
}
#endif

/* 
 * journal_forget: bforget() for potentially-journaled buffers.  We can
 * only do the bforget if there are no commits pending against the
 * buffer.  If the buffer is dirty in the current running transaction we
 * can safely unlink it. 
 *
 * bh may not be a journalled buffer at all - it may be a non-JBD
 * buffer which came off the hashtable.  Check for this.
 *
 * Decrements bh->b_count by one.
 * 
 * Allow this call even if the handle has aborted --- it may be part of
 * the caller's cleanup after an abort.
 */

void journal_forget (handle_t *handle, struct buffer_head *bh)
{
	transaction_t *transaction = handle->h_transaction;
	journal_t *journal = transaction->t_journal;
	struct journal_head *jh;

	BUFFER_TRACE(bh, "entry");

	lock_journal(journal);
	spin_lock(&journal_datalist_lock);

	if (!buffer_jbd(bh))
		goto not_jbd;
	jh = bh2jh(bh);

	if (jh->b_transaction == handle->h_transaction) {
		J_ASSERT_JH(jh, !jh->b_frozen_data);

		/* If we are forgetting a buffer which is already part
		 * of this transaction, then we can just drop it from
		 * the transaction immediately. */
		clear_bit(BH_Dirty, &bh->b_state);
		clear_bit(BH_JBDDirty, &bh->b_state);

		JBUFFER_TRACE(jh, "belongs to current transaction: unfile");
		J_ASSERT_JH(jh, !jh->b_committed_data);

		__journal_unfile_buffer(jh);
		jh->b_transaction = 0;

		/* 
		 * We are no longer going to journal this buffer.
		 * However, the commit of this transaction is still
		 * important to the buffer: the delete that we are now
		 * processing might obsolete an old log entry, so by
		 * committing, we can satisfy the buffer's checkpoint.
		 *
		 * So, if we have a checkpoint on the buffer, we should
		 * now refile the buffer on our BJ_Forget list so that
		 * we know to remove the checkpoint after we commit. 
		 */

		if (jh->b_cp_transaction) {
			__journal_file_buffer(jh, transaction, BJ_Forget);
		} else {