linux-kernel - Re: [PATCH v2 5/5] dax: handle media errors in dax_do

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Date:	Mon, 25 Apr 2016 01:31:14 -0700
From:	"hch@...radead.org" <hch@...radead.org>
To:	"Verma, Vishal L" <vishal.l.verma@...el.com>
Cc:	"hch@...radead.org" <hch@...radead.org>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"axboe@...com" <axboe@...com>, "jack@...e.cz" <jack@...e.cz>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

On Sat, Apr 23, 2016 at 06:08:37PM +0000, Verma, Vishal L wrote:
> direct_IO might fail with -EINVAL due to misalignment, or -ENOMEM due
> to some allocation failing, and I thought we should return the original
> -EIO in such cases so that the application doesn't lose the information
> that the bad block is actually causing the error.

EINVAL is a concern here.  Not due to the right error reported, but
because it means your current scheme is fundamentally broken - we
need to support I/O at any alignment for DAX I/O, and not fail due to
alignbment concernes for a highly specific degraded case.

I think this whole series need to go back to the drawing board as I
don't think it can actually rely on using direct I/O as the EIO
fallback.