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

To: "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx>
Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io
From: "hch@xxxxxxxxxxxxx" <hch@xxxxxxxxxxxxx>
Date: Mon, 25 Apr 2016 01:31:14 -0700
Cc: "hch@xxxxxxxxxxxxx" <hch@xxxxxxxxxxxxx>, "jmoyer@xxxxxxxxxx" <jmoyer@xxxxxxxxxx>, "axboe@xxxxxx" <axboe@xxxxxx>, "jack@xxxxxxx" <jack@xxxxxxx>, "linux-nvdimm@xxxxxxxxxxx" <linux-nvdimm@xxxxxxxxxxx>, "david@xxxxxxxxxxxxx" <david@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>, "linux-block@xxxxxxxxxxxxxxx" <linux-block@xxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "Wilcox, Matthew R" <matthew.r.wilcox@xxxxxxxxx>, "linux-fsdevel@xxxxxxxxxxxxxxx" <linux-fsdevel@xxxxxxxxxxxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "viro@xxxxxxxxxxxxxxxxxx" <viro@xxxxxxxxxxxxxxxxxx>
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In-reply-to: <1461434916.3695.7.camel@xxxxxxxxx>
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>
User-agent: Mutt/1.5.24 (2015-08-30)
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.

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