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

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Date:   Wed, 7 Apr 2021 12:13:55 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, dan.j.williams@...el.com, jack@...e.cz,
        viro@...iv.linux.org.uk, linux-btrfs@...r.kernel.org,
        david@...morbit.com, hch@....de, rgoldwyn@...e.de,
        Ritesh Harjani <riteshh@...il.com>
Subject: Re: [PATCH 1/3] fsdax: Factor helpers to simplify dax fault code

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?