linux-kernel - RE: [f2fs-dev] [PATCH 1/3] f2fs: flush symlink path to avoid broken symlink after POR

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Date:	Thu, 16 Apr 2015 18:33:29 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	'Jaegeuk Kim' <jaegeuk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: RE: [f2fs-dev] [PATCH 1/3] f2fs: flush symlink path to avoid broken
	symlink after POR

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Thursday, April 16, 2015 3:31 PM
> To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> linux-f2fs-devel@...ts.sourceforge.net
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 1/3] f2fs: flush symlink path to avoid broken symlink after POR
> 
> This patch tries to avoid broken symlink case after POR in best effort.
> This results in performance regression.
> But, if f2fs has inline_data and the target path is under 3KB-sized long,
> the page would be stored in its inode_block, so that there would be no
> performance regression.
> 
> Note that, if user wants to keep this file atomically, it needs to trigger
> dir->fsync.
> And, there is still a hole to produce broken symlink.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/namei.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 8055e30..5d990d8 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -324,6 +324,17 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
>  	d_instantiate(dentry, inode);
>  	unlock_new_inode(inode);
> 
> +	/*
> +	 * Let's flush symlink data in order to avoid broken symlink as much as
> +	 * possible. Nevertheless, fsyncing is the best way, but there is no
> +	 * way to get a file descriptor in order to flush that.
> +	 *
> +	 * Note that, it needs to do dir->fsync to make this recoverable.
> +	 * If the symlink path is stored into inline_data, there is no
> +	 * performance regression.
> +	 */
> +	filemap_write_and_wait_range(inode->i_mapping, 0, symlen);

One minor thing.

filemap_write_and_wait_range(inode->i_mapping, 0, symlen - 1);

Because we don't need to write out data exceed isize here.

Thanks,

> +
>  	if (IS_DIRSYNC(dir))
>  		f2fs_sync_fs(sbi->sb, 1);
>  	return err;
> --
> 2.1.1
> 
> 
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