Re: [RFC PATCH v4 6/9] ovl: implement overlayfs' ->write_inode operation

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, Nov 13, 2020 at 7:57 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
> Implement overlayfs' ->write_inode to sync dirty data
> and redirty overlayfs' inode if necessary.
>
> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
> ---
>  fs/overlayfs/super.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 883172ac8a12..82e001b97f38 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -390,6 +390,35 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
>         return ret;
>  }
>
> +static int ovl_write_inode(struct inode *inode,
> +                          struct writeback_control *wbc)
> +{
> +       struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> +       struct inode *upper = ovl_inode_upper(inode);
> +       unsigned long iflag = 0;
> +       int ret = 0;
> +
> +       if (!upper)
> +               return 0;
> +
> +       if (!ovl_should_sync(ofs))
> +               return 0;
> +
> +       if (upper->i_sb->s_op->write_inode)
> +               ret = upper->i_sb->s_op->write_inode(inode, wbc);
> +
> +       if (mapping_writably_mapped(upper->i_mapping) ||
> +           mapping_tagged(upper->i_mapping, PAGECACHE_TAG_WRITEBACK))
> +               iflag |= I_DIRTY_PAGES;
> +
> +       iflag |= upper->i_state & I_DIRTY_ALL;

How is I_DIRTY_SYNC added/removed from the overlay inode?

Thanks,
Miklos