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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 09/20] libmultipath: functions to indicate mapping failure in /dev/shm
Date: Thu, 12 Apr 2018 22:07:13 +0200	[thread overview]
Message-ID: <1523563633.4346.25.camel@suse.com> (raw)
In-Reply-To: <20180412183302.GL3103@octiron.msp.redhat.com>

On Thu, 2018-04-12 at 13:33 -0500, Benjamin Marzinski wrote:
> On Wed, Apr 04, 2018 at 06:16:16PM +0200, Martin Wilck wrote:
> > Create a simple API that indicates failure to create a map for a
> > certain WWID. This will allow multipathd to indicate to other tools
> > (in particular, "multipath -u" during udev processing) that
> > an attempt to create a map for a certain wwid failed.
> > 
> > The indicator is simply the existence of a file under
> > /dev/shm/multipath/failed_wwids.
> 
> I'm a little confused about the necessity of a lock file here.  What
> it
> the race that you are worried about? If two processes try to create a
> file at the same time, surely one of them will succeed. If two
> processes
> try to delete a file at the same time, it will get deleted.  If one
> process is trying to create a file and one is trying to remove it,
> the
> outcome depends on the who wins the race. But this is true whether
> you
> add a lock file to make those actions atomic or not. The same goes
> with
> stating a file that's being created or removed. As far a I can tell,
> this should work if you simply create an empty file without any
> locking.
> Are you worried about some odd errno due to a race?

My thinking was that it's generally a good thing to make file system
operations like this atomic, and the well-tested and mature open_file()
API was there ready to be used, thus I did.

You're probably right that the locking not strictly necessary. I don't
think it hurts, performance-wise the impact is quite low.
Do you require me to change this, or can we change it later?

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)

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  reply	other threads:[~2018-04-12 20:07 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 [this message]
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
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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