From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga14.intel.com ([192.55.52.115]:46661 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933355AbdIYOkf (ORCPT ); Mon, 25 Sep 2017 10:40:35 -0400 Date: Mon, 25 Sep 2017 10:45:35 -0400 From: Keith Busch To: Hannes Reinecke Cc: Christoph Hellwig , Jens Axboe , Sagi Grimberg , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org Subject: Re: [PATCH 8/9] nvme: implement multipath access to nvme subsystems Message-ID: <20170925144535.GB6331@localhost.localdomain> References: <20170925134031.10548-1-hch@lst.de> <20170925134031.10548-9-hch@lst.de> <1fb2f077-151a-b02f-2bf5-329ef5951a68@suse.de> <20170925135007.GA9725@lst.de> <55a10165-ac3c-f808-b031-6d907c314c30@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <55a10165-ac3c-f808-b031-6d907c314c30@suse.de> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Mon, Sep 25, 2017 at 04:05:17PM +0200, Hannes Reinecke wrote: > On 09/25/2017 03:50 PM, Christoph Hellwig wrote: > > On Mon, Sep 25, 2017 at 03:47:43PM +0200, Hannes Reinecke wrote: > >> Can't we make the multipath support invisible to the host? > >> IE check the shared namespaces before creating the device node, and just > >> move them under the existing namespaces if one exists? > > > > That was what my first version did, but various people talked me > > out of it. Unfortunately just multiplexing breaks a few things, > > including the userspace passthrough ioctls. > > > Care to give some specifics? > How would userspace passthrough be affected? Ioctls aside, if you've only one disk handle, it's a little difficult to compare iostats on each path, which can be useful for diagnosing issues. > I would've thought that we're sending the ioctl down one path, and we'd > be getting the completion back on the same path/queue/whatever. > (Unless we're talking multi-command ioctls, but those are evil anyway)