Hello Ben, In multipath manual document, multipath -q command is described as: "-q allow device tables with queue_if_no_path when multiathd is not running". However the command does not take effect when we testing it.
About use-case, In my opinion, sometimes we need to stop multipath service temporarily (for example: multipath version upgrade), but we do not want IO interrupt during those times even path down existed, so we can execute “multiath -q” to keep IO queue until we starting service after version upgrade. Cheers, Tang 发件人: "Benjamin Marzinski" <bmarz...@redhat.com> 收件人: Hannes Reinecke <h...@suse.de>, 抄送: Bart Van Assche <bart.vanass...@sandisk.com>, device-mapper development <dm-devel@redhat.com>, tang.jun...@zte.com.cn, zhang.ka...@zte.com.cn 日期: 2016/10/12 10:53 主题: Re: [dm-devel] [PATCH] libmultipath: fix multipath -q command logic 发件人: dm-devel-boun...@redhat.com On Tue, Oct 11, 2016 at 12:33:43PM +0200, Hannes Reinecke wrote: > On 10/11/2016 11:17 AM, tang.jun...@zte.com.cn wrote: > >Hello Hannes, Ben, > >Could you have a review for this patch, any comment will be highly > >appreciated. > > > >Thanks, > >Tang > > > > > > > > > >发件人: Christophe Varoqui <christophe.varo...@opensvc.com> > >收件人: tang.jun...@zte.com.cn, > >抄送: Bart Van Assche <bart.vanass...@sandisk.com>, device-mapper > >development <dm-devel@redhat.com>, zhang.ka...@zte.com.cn > >日期: 2016/10/11 14:59 > >主题: Re: [dm-devel] [PATCH] libmultipath: fix multipath -q > >command logic > >发件人: dm-devel-boun...@redhat.com > >------------------------------------------------------------------------ > > > > > > > >Hannes, Ben, > > > >are you ok with the solution to these two issues. > >Seems sane to me. > > > This actually is only part of the story. > > The whole idea of issuing 'multipath' is to check if a given path _should_ > be multipathed (as this is typically called from an udev event). > But as it's called from an udev event we cannot rely on the multipath daemon > to be started; we might just handle an event which came in before multipathd > got started from systemd. > So checking for the PID file is not enough, we need to check if the daemon > will be started eventually. > And in fact checking the PID file or calling mpath_connect() is equivalent, > with the added advantage the mpath_connect() will start the daemon _if > enabled by systemd_. > So this patch doesn't help much, as it doesn't solve the main problem of > figuring out if multipathd _should_ be started. > > I've done a patch for checking the '.wants' directories from systemd, but > this obviously will only work if the OS is systemd-based. > And it's not really perfect, as there are corner-cases where just checking > for the .wants directory is not enough. I think you are dealing with a different issue. the "-q" option for multipath just overrides the default behaviour of not enabling queue_if_no_path when creating a multipath device is multipathd isn't running. For this, we don't care if multipathd will start running in the future, because if/when multipathd does start up, it will set the queue_if_no_path flag itself. We only care about now, when we know it's not running. Really, I doubt that anyone ever uses the -q option. So your change in how multipath checks if multipathd is running is fine by me. However, you also changed what the "-q" option does. Previously, it just kept multipath from disabling "queue_if_no_path" on devices that were configured to have it, when multipathd wasn't running. With your code, doesn't it now make all devices set queue_if_no_path if multipathd isn't running, including devices that weren't configured to set it even when multipathd is running? Is there a reason for this? In general, setting "queue_if_no_path" when multiapthd isn't running is a bad idea, since the paths will never come back, and nothing will ever disable the queueing. That's why I said that I doubt anybody uses the option. Forcing all devices to set "queue_if_no_path", even if they weren't configured to, seems even less useful. Or is there actually a use-case that I'm missing here? -Ben > > Cheers, > > Hannes > -- > Dr. Hannes Reinecke zSeries & Storage > h...@suse.de +49 911 74053 688 > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg > GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
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