ext4: avoid issuing unnecessary barriers

[net-next-2.6.git] / fs / ext4 / fsync.c

/*
 *  linux/fs/ext4/fsync.c
 *
 *  Copyright (C) 1993  Stephen Tweedie (sct@redhat.com)
 *  from
 *  Copyright (C) 1992  Remy Card (card@masi.ibp.fr)
 *                      Laboratoire MASI - Institut Blaise Pascal
 *                      Universite Pierre et Marie Curie (Paris VI)
 *  from
 *  linux/fs/minix/truncate.c   Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  ext4fs fsync primitive
 *
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *
 *  Removed unnecessary code duplication for little endian machines
 *  and excessive __inline__s.
 *        Andi Kleen, 1997
 *
 * Major simplications and cleanup - we only need to do the metadata, because
 * we can depend on generic_block_fdatasync() to sync the data blocks.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/writeback.h>
#include <linux/jbd2.h>
#include <linux/blkdev.h>

#include "ext4.h"
#include "ext4_jbd2.h"

#include <trace/events/ext4.h>

/*
 * akpm: A new design for ext4_sync_file().
 *
 * This is only called from sys_fsync(), sys_fdatasync() and sys_msync().
 * There cannot be a transaction open by this task.
 * Another task could have dirtied this inode.  Its data can be in any
 * state in the journalling system.
 *
 * What we do is just kick off a commit and wait on it.  This will snapshot the
 * inode to disk.
 *
 * i_mutex lock is held when entering and exiting this function
 */

int ext4_sync_file(struct file *file, struct dentry *dentry, int datasync)
{
	struct inode *inode = dentry->d_inode;
	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
	int err, ret = 0;

	J_ASSERT(ext4_journal_current_handle() == NULL);

	trace_ext4_sync_file(file, dentry, datasync);

	ret = flush_aio_dio_completed_IO(inode);
	if (ret < 0)
		return ret;
	/*
	 * data=writeback:
	 *  The caller's filemap_fdatawrite()/wait will sync the data.
	 *  sync_inode() will sync the metadata
	 *
	 * data=ordered:
	 *  The caller's filemap_fdatawrite() will write the data and
	 *  sync_inode() will write the inode if it is dirty.  Then the caller's
	 *  filemap_fdatawait() will wait on the pages.
	 *
	 * data=journal:
	 *  filemap_fdatawrite won't do anything (the buffers are clean).
	 *  ext4_force_commit will write the file data into the journal and
	 *  will wait on that.
	 *  filemap_fdatawait() will encounter a ton of newly-dirtied pages
	 *  (they were dirtied by commit).  But that's OK - the blocks are
	 *  safe in-journal, which is all fsync() needs to ensure.
	 */
	if (ext4_should_journal_data(inode))
		return ext4_force_commit(inode->i_sb);

	if (!journal)
		ret = sync_mapping_buffers(inode->i_mapping);

	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
		goto out;

	/*
	 * The VFS has written the file data.  If the inode is unaltered
	 * then we need not start a commit.
	 */
	if (inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) {
		struct writeback_control wbc = {
			.sync_mode = WB_SYNC_ALL,
			.nr_to_write = 0, /* sys_fsync did this */
		};
		err = sync_inode(inode, &wbc);
		if (ret == 0)
			ret = err;
	}
out:
	if (journal && (journal->j_flags & JBD2_BARRIER))
		blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
	return ret;
}