Re: [PATCH 6/9] f2fs: zstd: Switch to the zstd-1.4.6 API

[Eric Biggers]

On Fri, Sep 18, 2020 at 09:47:32AM +0800, Chao Yu wrote:
> Ah, I got it.
> 
> Step of enabling compressed inode is not correct, we should touch an empty
> file, and then use 'chattr +c' on that file to enable compression, otherwise
> the race condition could be complicated to handle. So we need below diff to
> disallow setting compression flag on an non-empty file:
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 8a422400e824..b462db7898fd 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1836,6 +1836,8 @@ static int f2fs_setflags_common(struct inode *inode, 
> u32 iflags, u32 mask)
>               if (iflags & F2FS_COMPR_FL) {
>                       if (!f2fs_may_compress(inode))
>                               return -EINVAL;
> +                     if (get_dirty_pages(inode) || fi->i_compr_blocks)
> +                             return  -EINVAL;
> 
>                       set_compress_context(inode);
>               }

Why not:

        if (inode->i_size)
                return -EINVAL;