linux-kernel - Re: [PATCH] f2fs: compress: disallow disabling compress on non-empty compressed file

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Message-ID: <d5ac2754-85a3-8935-d1f8-829539664ca0@kernel.org>
Date:   Wed, 27 Oct 2021 10:30:24 +0800
From:   Chao Yu <chao@...nel.org>
To:     Hyeong-Jun Kim <hj514.kim@...sung.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Sungjong Seo <sj1557.seo@...sung.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: compress: disallow disabling compress on non-empty
 compressed file

On 2021/10/25 22:05, Hyeong-Jun Kim wrote:
> Compresse file and normal file has differ in i_addr addressing,
> specifically addrs per inode/block. So, we will face data loss, if we
> disable the compression flag on non-empty files. Therefore we should
> disallow not only enabling but disabling the compression flag on
> non-empty files. >

Hi Hyeong-Jun,

I think this makes sense.

But one more case may bypass below condition, could you please take a look
at this case:

touch file
chattr +c file
f2fs_io pinfile set file
fallocate file -o 0 -l 16384 -n
chattr -c file

So it's better to check F2FS_HAS_BLOCKS() as well in the condition?

Fixes: 4c8ff7095bef ("f2fs: support data compression")

Thanks,

> Signed-off-by: Sungjong Seo <sj1557.seo@...sung.com>
> Signed-off-by: Hyeong-Jun Kim <hj514.kim@...sung.com>
> ---
>   fs/f2fs/f2fs.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index b8e8f8c716b0..19146c834abd 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -4177,8 +4177,7 @@ static inline bool f2fs_disable_compressed_file(struct inode *inode)
>   
>   	if (!f2fs_compressed_file(inode))
>   		return true;
> -	if (S_ISREG(inode->i_mode) &&
> -		(get_dirty_pages(inode) || atomic_read(&fi->i_compr_blocks)))
> +	if (S_ISREG(inode->i_mode) && inode->i_size)
>   		return false;
>   
>   	fi->i_flags &= ~F2FS_COMPR_FL;
>