Re: [PATCH 02/15] iomap: Read page from srcmap if IOMAP_F_COW is set

[Christoph Hellwig <hch@xxxxxx>]

On Thu, Sep 05, 2019 at 10:06:37AM -0500, Goldwyn Rodrigues wrote:
> -	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
> +	} else if (iomap->flags & IOMAP_F_COW) {
> +		if (WARN_ON_ONCE(iomap->flags & IOMAP_F_BUFFER_HEAD)) {
> +			status = -EIO;
> +			goto out_no_page;
> +		}
> +		if (WARN_ON_ONCE(srcmap->type == IOMAP_HOLE &&
> +				 srcmap->addr != IOMAP_NULL_ADDR)) {

Well, we want HOLES to have IOMAP_NULL_ADDR everywhere, so not sure
why the assert is just here.

> +			status = -EIO;
> +			goto out_no_page;
> +		}
> +		status = __iomap_write_begin(inode, pos, len, page, srcmap);
> +	} else if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
>  		status = __block_write_begin_int(page, pos, len, NULL, iomap);
> -	else
> +	} else {
>  		status = __iomap_write_begin(inode, pos, len, page, iomap);
> +	}

Maybe a good way to structure this is:

	if (iomap->flags & IOMAP_F_BUFFER_HEAD) {
		if (WARN_ON_ONCE(iomap->flags & IOMAP_F_COW)) {
			status = -EIO;
			goto out_no_page;
		}
		status = __block_write_begin_int(page, pos, len, NULL, iomap);
	} else {
 		status = __iomap_write_begin(inode, pos, len, page,
				(iomap->flags & IOMAP_F_COW) ?  srcmap : iomap);
	}