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

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Message-ID: <x49r3dt7lhj.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 25 Apr 2016 11:32:08 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	"hch\@infradead.org" <hch@...radead.org>
Cc:	"Verma\, Vishal L" <vishal.l.verma@...el.com>,
	"axboe\@fb.com" <axboe@...com>, "jack\@suse.cz" <jack@...e.cz>,
	"linux-nvdimm\@ml01.01.org" <linux-nvdimm@...1.01.org>,
	"david\@fromorbit.com" <david@...morbit.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"xfs\@oss.sgi.com" <xfs@....sgi.com>,
	"linux-block\@vger.kernel.org" <linux-block@...r.kernel.org>,
	"linux-mm\@kvack.org" <linux-mm@...ck.org>,
	"Wilcox\, Matthew R" <matthew.r.wilcox@...el.com>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"akpm\@linux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-ext4\@vger.kernel.org" <linux-ext4@...r.kernel.org>,
	"viro\@zeniv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

"hch@...radead.org" <hch@...radead.org> writes:

> 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.

The only callers of dax_do_io are direct_IO methods.

Cheers,
Jeff