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Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

To: "hch\@infradead.org" <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
Date: Mon, 25 Apr 2016 11:32:08 -0400
Cc: "Verma\, Vishal L" <vishal.l.verma@xxxxxxxxx>, "axboe\@fb.com" <axboe@xxxxxx>, "jack\@suse.cz" <jack@xxxxxxx>, "linux-nvdimm\@ml01.01.org" <linux-nvdimm@xxxxxxxxxxx>, "david\@fromorbit.com" <david@xxxxxxxxxxxxx>, "linux-kernel\@vger.kernel.org" <linux-kernel@xxxxxxxxxxxxxxx>, "xfs\@oss.sgi.com" <xfs@xxxxxxxxxxx>, "linux-block\@vger.kernel.org" <linux-block@xxxxxxxxxxxxxxx>, "linux-mm\@kvack.org" <linux-mm@xxxxxxxxx>, "Wilcox\, Matthew R" <matthew.r.wilcox@xxxxxxxxx>, "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@xxxxxxxxxxxxxxx>, "akpm\@linux-foundation.org" <akpm@xxxxxxxxxxxxxxxxxxxx>, "linux-ext4\@vger.kernel.org" <linux-ext4@xxxxxxxxxxxxxxx>, "viro\@zeniv.linux.org.uk" <viro@xxxxxxxxxxxxxxxxxx>
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In-reply-to: <20160425083114.GA27556@xxxxxxxxxxxxx> (hch@xxxxxxxxxxxxx's message of "Mon, 25 Apr 2016 01:31:14 -0700")
References: <1459303190-20072-1-git-send-email-vishal.l.verma@xxxxxxxxx> <1459303190-20072-6-git-send-email-vishal.l.verma@xxxxxxxxx> <x49twj26edj.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20160420205923.GA24797@xxxxxxxxxxxxx> <1461434916.3695.7.camel@xxxxxxxxx> <20160425083114.GA27556@xxxxxxxxxxxxx>
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
"hch@xxxxxxxxxxxxx" <hch@xxxxxxxxxxxxx> 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

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