From: Martin Wilck <mwilck@suse.com>
To: Hannes Reinecke <hare@suse.de>,
Paolo Bonzini <pbonzini@redhat.com>,
Christoph Hellwig <hch@lst.de>
Cc: linux-scsi@vger.kernel.org, Daniel Wagner <dwagner@suse.de>,
Mike Snitzer <snitzer@redhat.com>,
emilne@redhat.com, linux-block@vger.kernel.org,
dm-devel@redhat.com,
"Martin K. Petersen" <martin.petersen@oracle.com>,
nkoenig@redhat.com, Bart Van Assche <Bart.VanAssche@sandisk.com>,
Alasdair G Kergon <agk@redhat.com>
Subject: Re: [dm-devel] [PATCH v5 3/3] dm mpath: add CONFIG_DM_MULTIPATH_SG_IO - failover for SG_IO
Date: Mon, 05 Jul 2021 15:48:10 +0200 [thread overview]
Message-ID: <a088aa5c8459c001403bda9384b38213f8232fc6.camel@suse.com> (raw)
In-Reply-To: <5909eff8-82fb-039e-41d3-1612c22498a9@suse.de>
On Mo, 2021-07-05 at 15:11 +0200, Hannes Reinecke wrote:
> On 7/5/21 3:02 PM, Paolo Bonzini wrote:
> > On 02/07/21 16:21, Martin Wilck wrote:
> > > > SG_IO gives you raw access to the SCSI logic unit, and you get
> > > > to
> > > > keep the pieces if anything goes wrong.
> > >
> > > That's a very fragile user space API, on the fringe of being
> > > useless
> > > IMO.
> >
> > Indeed. If SG_IO is for raw access to an ITL nexus, it shouldn't
> > be
> > supported at all by mpath devices. If on the other hand SG_IO is
> > for
> > raw access to a LUN, there is no reason for it to not support
> > failover.
> >
> Or we look at IO_URING_OP_URING_CMD, to send raw cdbs via io_uring.
> And delegate SG_IO to raw access to an ITL nexus.
> Doesn't help with existing issues, but should get a clean way
> forward.
I still have to understand how this would help with the retrying
semantics. Wouldn't we get the exact same problem if a path error
occurs?
Regards,
Martin
WARNING: multiple messages have this Message-ID (diff)
From: Martin Wilck <mwilck@suse.com>
To: Hannes Reinecke <hare@suse.de>,
Paolo Bonzini <pbonzini@redhat.com>,
Christoph Hellwig <hch@lst.de>
Cc: Mike, Daniel Wagner <dwagner@suse.de>,
Snitzer <snitzer@redhat.com>,
emilne@redhat.com,
"Martin K. Petersen" <martin.petersen@oracle.com>,
linux-block@vger.kernel.org, dm-devel@redhat.com,
linux-scsi@vger.kernel.org, nkoenig@redhat.com,
Bart Van Assche <Bart.VanAssche@sandisk.com>,
Alasdair G Kergon <agk@redhat.com>
Subject: Re: [dm-devel] [PATCH v5 3/3] dm mpath: add CONFIG_DM_MULTIPATH_SG_IO - failover for SG_IO
Date: Mon, 05 Jul 2021 15:48:10 +0200 [thread overview]
Message-ID: <a088aa5c8459c001403bda9384b38213f8232fc6.camel@suse.com> (raw)
In-Reply-To: <5909eff8-82fb-039e-41d3-1612c22498a9@suse.de>
On Mo, 2021-07-05 at 15:11 +0200, Hannes Reinecke wrote:
> On 7/5/21 3:02 PM, Paolo Bonzini wrote:
> > On 02/07/21 16:21, Martin Wilck wrote:
> > > > SG_IO gives you raw access to the SCSI logic unit, and you get
> > > > to
> > > > keep the pieces if anything goes wrong.
> > >
> > > That's a very fragile user space API, on the fringe of being
> > > useless
> > > IMO.
> >
> > Indeed. If SG_IO is for raw access to an ITL nexus, it shouldn't
> > be
> > supported at all by mpath devices. If on the other hand SG_IO is
> > for
> > raw access to a LUN, there is no reason for it to not support
> > failover.
> >
> Or we look at IO_URING_OP_URING_CMD, to send raw cdbs via io_uring.
> And delegate SG_IO to raw access to an ITL nexus.
> Doesn't help with existing issues, but should get a clean way
> forward.
I still have to understand how this would help with the retrying
semantics. Wouldn't we get the exact same problem if a path error
occurs?
Regards,
Martin
--
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dm-devel@redhat.com
https://listman.redhat.com/mailman/listinfo/dm-devel
next prev parent reply other threads:[~2021-07-05 13:48 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-28 15:15 [PATCH v5 0/3] scsi/dm: dm_blk_ioctl(): implement failover for SG_IO on dm-multipath mwilck
2021-06-28 15:15 ` [dm-devel] " mwilck
2021-06-28 15:15 ` [PATCH v5 1/3] scsi: scsi_ioctl: export __scsi_result_to_blk_status() mwilck
2021-06-28 15:15 ` [dm-devel] " mwilck
2021-06-28 15:15 ` [PATCH v5 2/3] scsi: scsi_ioctl: add sg_io_to_blk_status() mwilck
2021-06-28 15:15 ` [dm-devel] " mwilck
2021-06-28 15:15 ` [PATCH v5 3/3] dm mpath: add CONFIG_DM_MULTIPATH_SG_IO - failover for SG_IO mwilck
2021-06-28 15:15 ` [dm-devel] " mwilck
2021-07-01 7:56 ` Christoph Hellwig
2021-07-01 7:56 ` [dm-devel] " Christoph Hellwig
2021-07-01 10:35 ` Martin Wilck
2021-07-01 10:35 ` [dm-devel] " Martin Wilck
2021-07-01 11:34 ` Christoph Hellwig
2021-07-01 11:34 ` [dm-devel] " Christoph Hellwig
2021-07-02 14:21 ` Martin Wilck
2021-07-02 14:21 ` Martin Wilck
2021-07-05 13:02 ` Paolo Bonzini
2021-07-05 13:02 ` Paolo Bonzini
2021-07-05 13:11 ` Hannes Reinecke
2021-07-05 13:11 ` Hannes Reinecke
2021-07-05 13:48 ` Martin Wilck [this message]
2021-07-05 13:48 ` Martin Wilck
2021-07-06 10:13 ` Paolo Bonzini
2021-07-06 10:13 ` Paolo Bonzini
2021-07-01 11:06 ` Paolo Bonzini
2021-07-01 11:06 ` [dm-devel] " Paolo Bonzini
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