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SubjectRe: 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@oss.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@suse.cz>
SUSE Labs, CR
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