linux-kernel - Re: [PATCH] fat: issue flush after the writeback of FAT

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Date:   Mon, 8 Apr 2019 20:41:00 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Hou Tao <houtao1@...wei.com>
Cc:     hirofumi@...l.parknet.co.jp, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, jack@...e.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fat: issue flush after the writeback of FAT

On Tue, Apr 09, 2019 at 11:01:58AM +0800, Hou Tao wrote:
> fsync() needs to make sure the data & meta-data of file are persistent
> after the return of fsync(), even when a power-failure occurs later.
> In the case of fat-fs, the FAT belongs to the meta-data of file,
> so we need to issue a flush after the writeback of FAT instead before.
> 
> Also bail out early when any stage of fsync fails.
> 
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  fs/fat/file.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/fat/file.c b/fs/fat/file.c
> index b3bed32946b1..0e3ed79fcc3f 100644
> --- a/fs/fat/file.c
> +++ b/fs/fat/file.c
> @@ -193,12 +193,17 @@ static int fat_file_release(struct inode *inode, struct file *filp)
>  int fat_file_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
>  {
>  	struct inode *inode = filp->f_mapping->host;
> -	int res, err;
> +	int err;
> +
> +	err = __generic_file_fsync(filp, start, end, datasync);
> +	if (err)
> +		return err;
>  
> -	res = generic_file_fsync(filp, start, end, datasync);
>  	err = sync_mapping_buffers(MSDOS_SB(inode->i_sb)->fat_inode->i_mapping);

Huh.  I would've thought that flushing the FAT would also be required
at the end of a WB_SYNC_ALL (aka data integrity) writepages call?

The patch itself seems good, though.

--D

> +	if (err)
> +		return err;
>  
> -	return res ? res : err;
> +	return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
>  }
>  
>  
> -- 
> 2.16.2.dirty
>