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

[ruansy.fnst@xxxxxxxxxxx]

> -----Original Message-----
> From: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Sent: Wednesday, April 7, 2021 7:14 PM
> To: Ruan, Shiyang/阮 世阳 <ruansy.fnst@xxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-xfs@xxxxxxxxxxxxxxx;
> linux-nvdimm@xxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> darrick.wong@xxxxxxxxxx; dan.j.williams@xxxxxxxxx; jack@xxxxxxx;
> viro@xxxxxxxxxxxxxxxxxx; linux-btrfs@xxxxxxxxxxxxxxx; david@xxxxxxxxxxxxx;
> hch@xxxxxx; rgoldwyn@xxxxxxx; Ritesh Harjani <riteshh@xxxxxxxxx>
> 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?

Yes, I'll fix it.


--
Thanks,
Ruan Shiyang.