linux-kernel - Re: [PATCH 0/2] dm mpath: Interface for explicit probing of active paths

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Message-ID: <aCNzf7MJa-hLQpmv@redhat.com>
Date: Tue, 13 May 2025 12:29:51 -0400
From: Benjamin Marzinski <bmarzins@...hat.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Hannes Reinecke <hare@...e.de>, Kevin Wolf <kwolf@...hat.com>,
        Martin Wilck <mwilck@...e.com>, dm-devel@...ts.linux.dev,
        hreitz@...hat.com, mpatocka@...hat.com, snitzer@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] dm mpath: Interface for explicit probing of active
 paths

On Mon, May 12, 2025 at 11:49:19PM -0700, Christoph Hellwig wrote:
> On Tue, May 13, 2025 at 08:32:12AM +0200, Hannes Reinecke wrote:
> > Reservations and stuff.
> 
> They should use the kernel persistent reservation API.

Currently QEMU isn't sending Persistent Reservation requests to
multipath devices at all. It's sending those directly to the underlying
scsi devices. The issue here is with all the other SCSI commands that
users want to send to their SCSI passthrough device that is actually a
multipath device on top of a number of SCSI paths. They expect to
get back the actual sense and status information, so QEMU needs to
send them via SG_IOs.

Without reading that sense and status information in kernel, the
multipath target can't know if it needs to fail a path and retry the
ioctl down a different path. QEMU can read this information, but it
doesn't know what path the multipath device send the ioctl down. This
patch just gives users a way to check the paths in the active pathgroup
(which all should be able to handle IO) and fail those that can't.
While QEMU is the driver of this, it's completely general functionality.

-Ben

> 
> > There are customer who use GPFS ...
> 
> Supporting illegal binary only modules that is already enough of a
> reason to NAK this.