linux-ext4 - Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io

Open Source and information security mailing list archives

Date:	Thu, 5 May 2016 21:45:07 +0000
From:	"Verma, Vishal L" <vishal.l.verma@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"hch@...radead.org" <hch@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"xfs@....sgi.com" <xfs@....sgi.com>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"axboe@...com" <axboe@...com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"david@...morbit.com" <david@...morbit.com>,
	"jack@...e.cz" <jack@...e.cz>, "matthew@....cx" <matthew@....cx>
Subject: Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io

On Thu, 2016-05-05 at 08:22 -0700, Christoph Hellwig wrote:
> On Thu, May 05, 2016 at 08:15:32AM -0700, Dan Williams wrote:
> > 
> > > 
> > > Agreed - makig O_DIRECT less direct than not having it is plain
> > > stupid,
> > > and I somehow missed this initially.
> > Of course I disagree because like Dave argues in the msync case we
> > should do the correct thing first and make it fast later, but also
> > like Dave this arguing in circles is getting tiresome.
> We should do the right thing first, and make it fast later.  But this
> proposal is not getting it right - it still does not handle errors
> for the fast path, but magically makes it work for direct I/O by
> in general using a less optional path for O_DIRECT.  It's getting the
> worst of all choices.
> 
> As far as I can tell the only sensible option is to:
> 
>  - always try dax-like I/O first
>  - have a custom get_user_pages + rw_bytes fallback handles bad blocks
>    when hitting EIO

I'm not sure I completely understand how this will work? Can you explain
a bit? Would we have to export rw_bytes up to layers above the pmem
driver? Where does get_user_pages come in?

> 
> And then we need to sort out the concurrent write synchronization.
> Again there I think we absolutely have to obey Posix for the !O_DIRECT
> case and can avoid it for O_DIRECT, similar to the existing non-DAX
> semantics.  If we want any special additional semantics we _will_ need
> a special O_DAX flag.
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@...ts.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives