linux-kernel - Re: ext3: call blkdev_issue

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Date:	Fri, 16 Jan 2009 17:30:39 +0100
From:	Jan Kara <jack@...e.cz>
To:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
Cc:	Theodore Tso <tytso@....EDU>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Pavel Machek <pavel@...e.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>, sandeen@...hat.com,
	fernando@....ac.jp
Subject: Re: ext3: call blkdev_issue_flush on fsync

On Fri 16-01-09 22:55:01, Fernando Luis Vázquez Cao wrote:
> To ensure that bits are truly on-disk after an fsync or fdatasync, we
> should force a disk flush explicitly when there is dirty data/metadata
> and the journal didn't emit a write barrier (either because metadata is
> not being synched or barriers are disabled).
> 
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
> ---
  Only two minor nits:

> --- linux-2.6.29-rc1-orig/fs/ext3/fsync.c	2008-12-25 08:26:37.000000000 +0900
> +++ linux-2.6.29-rc1/fs/ext3/fsync.c	2009-01-16 22:18:53.000000000 +0900
> @@ -27,6 +27,7 @@
>  #include <linux/sched.h>
>  #include <linux/writeback.h>
>  #include <linux/jbd.h>
> +#include <linux/blkdev.h>
>  #include <linux/ext3_fs.h>
>  #include <linux/ext3_jbd.h>
>  
> @@ -45,6 +46,8 @@
>  int ext3_sync_file(struct file * file, struct dentry *dentry, int datasync)
>  {
>  	struct inode *inode = dentry->d_inode;
> +	journal_t *journal = EXT3_SB(inode->i_sb)->s_journal;
> +	unsigned long i_state = inode->i_state;
>  	int ret = 0;
>  
>  	J_ASSERT(ext3_journal_current_handle() == NULL);
> @@ -69,23 +72,33 @@ int ext3_sync_file(struct file * file, s
>  	 */
>  	if (ext3_should_journal_data(inode)) {
>  		ret = ext3_force_commit(inode->i_sb);
> +		if (!(journal->j_flags & JFS_BARRIER))
> +			goto no_journal_barrier;
>  		goto out;
>  	}
>  
> -	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> -		goto out;
> +	if (datasync && !(i_state & I_DIRTY_DATASYNC))
> +		goto flush_blkdev;
>  
>  	/*
>  	 * 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)) {
> +	if (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 */
>  		};
>  		ret = sync_inode(inode, &wbc);
> +		if (journal && !(journal->j_flags & JFS_BARRIER))
> +			goto no_journal_barrier;
  I cannot imagine "journal" will be NULL here.
  And we can also optimize here a bit and do "goto out" because here
we know the barrier has been issued.

>  	}
> +
> +flush_blkdev:
> +	if (!(i_state & I_DIRTY_PAGES))
> +		goto out;
> +no_journal_barrier:
> +	blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
>  out:
>  	return ret;
>  }

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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