[dm-devel] [PATCH] libmultipath: fix multipath -q command logic

[Hannes Reinecke]

On 10/11/2016 11:17 AM, tang.junhui at 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.varoqui at opensvc.com>
> 收件人:         tang.junhui at zte.com.cn,
> 抄送:        Bart Van Assche <bart.vanassche at sandisk.com>, device-mapper
> development <dm-devel at redhat.com>, zhang.kai16 at 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-bounces at 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.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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