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

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Message-ID: <aCrCYbvOJs44Kj5a@infradead.org>
Date: Sun, 18 May 2025 22:32:17 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Benjamin Marzinski <bmarzins@...hat.com>
Cc: Christoph Hellwig <hch@...radead.org>, 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 Fri, May 16, 2025 at 12:06:21PM -0400, Benjamin Marzinski wrote:
> I've run into SCSI arrays that always act like they were called with the
> ALL_TG_PT flag set (or perhaps they were just configured that way, I
> never could get a straight answer about that).

Hmm, that's pretty strange.

> libmpathpersist accepts
> this flag, and only sends one registration per initiator & target device
> when it's set, instead of one per initator & target port.

With "this flag" you mean ALL_TG_PT?

> dm-multipath
> currently doesn't have the knowledge necessary to figure out which
> devices it needs to send reservations to, even if the kernel PR API
> supported this.
> 
> But I supposed it could just send the registration normally down one
> path and if that works, it could just ignore the existing key when it
> sends the registration down all the other paths.

We could add support for a similar flag to the kernel PR API.  The
problem is to figure out how to discover support for it.  What does
the library do for that currently?