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Wed, 14 May 2025 06:39:25 +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 IQm8OJ06JGjZcQAAD6G6ig (envelope-from ); Wed, 14 May 2025 06:39:25 +0000 Message-ID: <37bb9993-baaa-4dc8-b5d4-e66201e4a462@suse.de> Date: Wed, 14 May 2025 08:39:25 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] dm mpath: Interface for explicit probing of active paths To: Benjamin Marzinski , Christoph Hellwig Cc: Kevin Wolf , Martin Wilck , dm-devel@lists.linux.dev, hreitz@redhat.com, mpatocka@redhat.com, snitzer@kernel.org, linux-kernel@vger.kernel.org References: <20250429165018.112999-1-kwolf@redhat.com> <47dd225b433b0df585a25084a2e793344eeda239.camel@suse.com> <0340c51e-6f89-4799-b2f1-19c785a19ff2@suse.de> Content-Language: en-US From: Hannes Reinecke In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Level: X-Spam-Flag: NO X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; 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.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid,suse.de:email] X-Spam-Score: -4.30 On 5/13/25 18:29, Benjamin Marzinski wrote: > 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. > Ouch. Different reservations on different paths? Really? How do you manage to keep the reservations up-to-date? My recommendation is to use the _same_ reservation on all paths, precisely to avoid having to re-do reservations on path failure. And for that scenario the kernel persistent reservation API would work fine. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich