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Wed, 28 May 2025 20:44:17 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id JTVSG6F1N2g6NgAAD6G6ig (envelope-from ); Wed, 28 May 2025 20:44:17 +0000 Message-ID: <914a7e9207c028a74d5c579273b4c71b555619d7.camel@suse.com> Subject: Re: [PATCH 0/2] dm mpath: Interface for explicit probing of active paths From: Martin Wilck To: Christoph Hellwig , Benjamin Marzinski Cc: Kevin Wolf , dm-devel@lists.linux.dev, hreitz@redhat.com, mpatocka@redhat.com, snitzer@kernel.org, linux-kernel@vger.kernel.org, Hannes Reinecke Date: Wed, 28 May 2025 22:44:16 +0200 In-Reply-To: References: <20250429165018.112999-1-kwolf@redhat.com> <47dd225b433b0df585a25084a2e793344eeda239.camel@suse.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[suse.com:mid,imap1.dmz-prg2.suse.org:helo]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:mid] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -4.30 On Sun, 2025-05-18 at 22:32 -0700, Christoph Hellwig wrote: > 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). >=20 > Hmm, that's pretty strange. >=20 > > libmpathpersist accepts > > this flag, and only sends one registration per initiator & target > > device > > when it's set, instead of one per initator & target port. >=20 > With "this flag" you mean ALL_TG_PT? multipath-tools allows setting the flag "all_tg_pt" in multipath.conf for certain storage devices or multipath maps. If this flag is set, mpathpersist will always act as if the --param-alltgpt flag was given. This means that the REGISTER commands are sent once per initiator port (SCSI host) only, instead of once per I_T nexus. By default,=C2=A0the all_tg_pt flag is not set for any device, not even for EMC VNX, where Ben observed the described behavior. It seems that devices that behave like this are a rare exception. > > 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. > >=20 > > 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. >=20 > We could add support for a similar flag to the kernel PR API.=C2=A0 The > problem is to figure out how to discover support for it.=C2=A0 What does > the library do for that currently? dm-multipath has no knowledge about target or initiator ports, and I fail to see how we could provide this knowledge to it without adding yet another layering violation. Just sending the command once will not be sufficient if there are multiple local ports. Regards Martin