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From: Martin Wilck <mwilck@suse.com>
To: Benjamin Marzinski <bmarzins@redhat.com>
Cc: dm-devel@redhat.com, Julian Andres Klode <julian.klode@canonical.com>
Subject: Re: [PATCH v4 18/20] multipath -u: quick check if path is multipathed
Date: Fri, 13 Apr 2018 00:19:12 +0200	[thread overview]
Message-ID: <1523571552.4346.108.camel@suse.com> (raw)
In-Reply-To: <20180412184618.GT3103@octiron.msp.redhat.com>

On Thu, 2018-04-12 at 13:46 -0500, Benjamin Marzinski wrote:
> On Wed, Apr 04, 2018 at 06:16:25PM +0200, Martin Wilck wrote:
> > With "find_multipaths smart", we accept paths as valid if they are
> > already part of a multipath map. This patch avoids doing a full
> > path
> > and device-mapper map scan for this case, speeding up "multipath
> > -u"
> > considerably.
> 
> I feel like this supports my idea from 17/20. I really think that in
> smart mode, the only time we should be claiming a device as multipath
> is
> on an add event, if it has always been claimed (or pretend claimed)
> as a
> multipath path, or if it is currently a multipath path. Once we have
> let
> a uevent go by for a path without setting SYSTEMD_READY=0, anything
> else
> is free to use it, and we simply can't safely set SYSTEMD_READY=0,
> unless we know that multipathd has already grabbed the device.

We have to remember that in the udev db then. That doesn't work for
coldplug aside, but we agree that's not an issue. By checking a
suitable udev variable, we can make sure that we never set
SYSTEMD_READY=0 after having released the device to the system.

>  I feel
> like checking the wwids file should give you confidence that a device
> either currently is a multipath path, or has always been claimed as
> one.
> However, this patch can fix any loop holes where a device isn't in
> the
> wwids file, but it multipathed (I don't know of any offhand).

multipath -u can't assume that multipathd is running. The map may have
been set up in the initrd, and thus would not necessarily be in the
WWIDs file in the root FS. 

Currently multipath -u scans all paths and maps in this case, just to
figure out if the given path is maybe already part of a map. My patch
was just meant as a shortcut for this case. If we could rely on the
WWIDs file that would be even easier, but I don't think we can.

Martin

-- 
Dr. Martin Wilck <mwilck@suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)

--
dm-devel mailing list
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https://www.redhat.com/mailman/listinfo/dm-devel

  reply	other threads:[~2018-04-12 22:19 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-04 16:16 [PATCH v4 00/20] multipath path classification Martin Wilck
2018-04-04 16:16 ` [PATCH v4 01/20] Revert "multipath: ignore -i if find_multipaths is set" Martin Wilck
2018-04-04 16:16 ` [PATCH v4 02/20] Revert "multipathd: imply -n " Martin Wilck
2018-04-04 16:16 ` [PATCH v4 03/20] libmultipath: should_multipath: keep existing maps Martin Wilck
2018-04-04 16:16 ` [PATCH v4 04/20] multipath -u -i: respect entries in WWIDs file Martin Wilck
2018-04-04 16:16 ` [PATCH v4 05/20] libmultipath: trigger change uevent on new device creation Martin Wilck
2018-04-04 16:16 ` [PATCH v4 06/20] libmultipath: trigger path uevent only when necessary Martin Wilck
2018-04-04 16:16 ` [PATCH v4 07/20] libmultipath: change find_multipaths option to multi-value Martin Wilck
2018-04-12 18:32   ` Benjamin Marzinski
2018-04-13 18:23   ` Martin Wilck
2018-04-04 16:16 ` [PATCH v4 08/20] libmultipath: use const char* in open_file() Martin Wilck
2018-04-04 16:16 ` [PATCH v4 09/20] libmultipath: functions to indicate mapping failure in /dev/shm Martin Wilck
2018-04-12 18:33   ` Benjamin Marzinski
2018-04-12 20:07     ` Martin Wilck
2018-04-12 21:27       ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 10/20] libmultipath: indicate wwid failure in dm_addmap_create() Martin Wilck
2018-04-12 18:33   ` Benjamin Marzinski
2018-04-12 20:16     ` Martin Wilck
2018-04-12 20:22       ` Martin Wilck
2018-04-12 21:32         ` Benjamin Marzinski
2018-04-12 22:43           ` Martin Wilck
2018-04-04 16:16 ` [PATCH v4 11/20] multipath -u: common code path for result message Martin Wilck
2018-04-12 18:34   ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 12/20] multipath -u: change output to environment/key format Martin Wilck
2018-04-12 18:35   ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 13/20] multipath -u: treat failed wwids as invalid Martin Wilck
2018-04-12 18:35   ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 14/20] multipath -u: add DM_MULTIPATH_DEVICE_PATH=2 for "maybe" Martin Wilck
2018-04-04 16:16 ` [PATCH v4 15/20] libmultipath: implement find_multipaths_timeout Martin Wilck
2018-04-12 18:35   ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 16/20] multipath -u : set FIND_MULTIPATHS_WAIT_UNTIL from /dev/shm Martin Wilck
2018-04-12 18:36   ` Benjamin Marzinski
2018-04-12 20:35     ` Martin Wilck
2018-04-12 21:35       ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 18/20] multipath -u: quick check if path is multipathed Martin Wilck
2018-04-12 18:46   ` Benjamin Marzinski
2018-04-12 22:19     ` Martin Wilck [this message]
2018-04-13 16:12       ` Benjamin Marzinski
2018-04-13 17:59         ` Martin Wilck
2018-04-04 16:16 ` [PATCH v4 19/20] libmultipath: enable find_multipaths "smart" Martin Wilck
2018-04-12 18:47   ` Benjamin Marzinski
2018-04-12 22:27     ` Martin Wilck
2018-04-13 15:59       ` Benjamin Marzinski
2018-04-04 16:16 ` [PATCH v4 20/20] multipath.rules: find_multipaths "smart" logic Martin Wilck
2018-04-12 18:48   ` Benjamin Marzinski
2018-04-13 16:01     ` Benjamin Marzinski

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