linux-ext4 - Re: [PATCH 5/5] dax: handle media errors in dax_do

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Date:	Sat, 26 Mar 2016 09:53:59 -0700
From:	"hch@...radead.org" <hch@...radead.org>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	"Verma, Vishal L" <vishal.l.verma@...el.com>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"jack@...e.cz" <jack@...e.cz>, "axboe@...com" <axboe@...com>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"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>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>
Subject: Re: [PATCH 5/5] dax: handle media errors in dax_do_io

On Fri, Mar 25, 2016 at 02:42:37PM -0700, Dan Williams wrote:
> That's their prerogative otherwise you are precluding an alternate
> handling of a dax_do_io() failure.  Maybe a fs or upper layer can
> recover in a different manner than re-submit the I/O to the
> __blockdev_direct_IO path.

Let's keep the interface separate because they are, well separate.
There is a reason direct I/O falls back to buffered I/O by returning
and error if it can't handle it instead of handling all the magic.

I also really want to get rid of get_block as soon as possible for
DAX and direct I/O.  For DAX that should actually be possible
really quickly, while direct I/O might take some time and will
be have to be gradual.  So tighter integration of the two interface is
not just bad design, but actively harmful at this point in time.
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