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

[hch@xxxxxxxxxxxxx]

On Mon, Apr 25, 2016 at 05:14:36PM +0000, Verma, Vishal L wrote:
> - Application hits EIO doing dax_IO or load/store io
> 
> - It checks badblocks and discovers it's files have lost data
> 
> - It write()s those sectors (possibly converted to file offsets using
> fiemap)
> ?? ?? * This triggers the fallback path, but if the application is doing
> this level of recovery, it will know the sector is bad, and write the
> entire sector

This sounds like a mess.

> I think if we want to keep allowing arbitrary alignments for the
> dax_do_io path, we'd need:
> 1. To represent badblocks at a finer granularity (likely cache lines)
> 2. To allow the driver to do IO to a *block device* at sub-sector
> granularity

It's not a block device if it supports DAX.  It's byte addressable
memory masquerading as a block device.