答复: Re: [PATCH] libmultipath: fix multipath -q command logic

[tang.junhui@zte.com.cn]

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Hello Hannes,
check_daemon() now is only used to determine whether to set/remove 
queue_if_no_path feature for
mapped devices, which you said maybe another issue, we are looking forward 
for your patch.

Thanks,
Tang



发件人:         Hannes Reinecke <hare@suse.de>
收件人:         tang.junhui@zte.com.cn, bmarzins@redhat.com, 
抄送:   Bart Van Assche <bart.vanassche@sandisk.com>, device-mapper 
development <dm-devel@redhat.com>, zhang.kai16@zte.com.cn
日期:   2016/10/11 18:42
主题:   Re: [dm-devel] [PATCH] libmultipath: fix multipath -q command 
logic
发件人: dm-devel-bounces@redhat.com



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

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