Re: [PATCH v2 11/18] mm/filemap: Convert filemap_update_page to return an errno

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Fri, Nov 06, 2020 at 09:37:46AM +0100, Christoph Hellwig wrote:
>  
> -	error = AOP_TRUNCATED_PAGE;
> -	if (!page->mapping)
> -		goto unlock;
> -	if (filemap_range_uptodate(iocb, mapping, iter, page)) {
> +	if (!page->mapping) {
>  		unlock_page(page);
> -		return 0;
> +		put_page(page);
> +		return AOP_TRUNCATED_PAGE;
>  	}
>  
> -	error = -EAGAIN;
> -	if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
> -		goto unlock;
> +	if (!filemap_range_uptodate(iocb, mapping, iter, page)) {
> +		error = -EAGAIN;
> +		if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
> +			goto unlock;
> +		return filemap_read_page(iocb->ki_filp, mapping, page);
> +	}
>  
> -	error = filemap_read_page(iocb->ki_filp, mapping, page);
> -	if (error)
> -		goto error;
> -	return 0;
>  unlock:
>  	unlock_page(page);
> -error:
> -	put_page(page);
>  	return error;
>  }

It works out to be a little more complicated than that because
filemap_read_page() can also return AOP_TRUNCATED_PAGE.  Here's what I
currently have:

        if (!page->mapping)
                goto truncated;

        error = 0;
        if (filemap_range_uptodate(iocb, mapping, iter, page))
                goto unlock;

        error = -EAGAIN;
        if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
                goto unlock;

        error = filemap_read_page(iocb->ki_filp, mapping, page);
        if (error == AOP_TRUNCATED_PAGE)
                put_page(page);
        return error;
truncated:
        error = AOP_TRUNCATED_PAGE;
        put_page(page);
unlock:
        unlock_page(page);
        return error;
}