Re: [PATCH 1/3] fsdax: Factor helpers to simplify dax fault code

From: Matthew Wilcox <willy@infradead.org>
To: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org,
	darrick.wong@oracle.com, dan.j.williams@intel.com, jack@suse.cz,
	viro@zeniv.linux.org.uk, linux-btrfs@vger.kernel.org,
	david@fromorbit.com, hch@lst.de, rgoldwyn@suse.de,
	Ritesh Harjani <riteshh@gmail.com>
Subject: Re: [PATCH 1/3] fsdax: Factor helpers to simplify dax fault code
Date: Wed, 7 Apr 2021 12:13:55 +0100	[thread overview]
Message-ID: <20210407111355.GD2531743@casper.infradead.org> (raw)
In-Reply-To: <20210407063207.676753-2-ruansy.fnst@fujitsu.com>

On Wed, Apr 07, 2021 at 02:32:05PM +0800, Shiyang Ruan wrote:
> +static int dax_fault_cow_page(struct vm_fault *vmf, struct iomap *iomap,
> +		loff_t pos, vm_fault_t *ret)
> +{
> +	int error = 0;
> +	unsigned long vaddr = vmf->address;
> +	sector_t sector = dax_iomap_sector(iomap, pos);
> +
> +	switch (iomap->type) {
> +	case IOMAP_HOLE:
> +	case IOMAP_UNWRITTEN:
> +		clear_user_highpage(vmf->cow_page, vaddr);
> +		break;
> +	case IOMAP_MAPPED:
> +		error = copy_cow_page_dax(iomap->bdev, iomap->dax_dev,
> +						sector, vmf->cow_page, vaddr);
> +		break;
> +	default:
> +		WARN_ON_ONCE(1);
> +		error = -EIO;
> +		break;
> +	}
> +
> +	if (error)
> +		return error;
> +
> +	__SetPageUptodate(vmf->cow_page);
> +	*ret = finish_fault(vmf);
> +	if (!*ret)
> +		*ret = VM_FAULT_DONE_COW;
> +	return 0;
> +}
...

> +		error = dax_fault_cow_page(vmf, &iomap, pos, &ret);
>  		if (error)
> +			ret = dax_fault_return(error);
>  		goto finish_iomap;

This seems unnecessarily complex.  Why not return the vm_fault_t instead of
returning the errno and then converting it?