linux-kernel - Re: [PATCH 001 of 6] md: Send online/offline uevents when an md array starts/stops.

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Date:	Thu, 9 Nov 2006 11:17:57 +1100
From:	Neil Brown <neilb@...e.de>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Greg KH <gregkh@...e.de>, Andrew Morton <akpm@...l.org>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 001 of 6] md: Send online/offline uevents when an md
	array starts/stops.

On Wednesday November 8, kay.sievers@...y.org wrote:
> 
> Is there a sysfs file or something similar(we could also call a md-tool)
> udev could look at, before it tries to open the device? Like:
>   KERNEL=="md*", ATTR{state}=="active", IMPORT{program}= ...

If the /sys/block/mdX directory exists at all, it is safe to open the
device-special file.  But that is racy.  It could disappear between
checking that the dir exists, and opening the device-special-file.

I still think it would make SO much sense if /sys/block/md4/dev were a
device-special-file instead of a (silly) ascii file with 9:4.  Then
this race could be closed.  But I feel that is a battle I've never
going to win.

You could look at /sys/block/mdX/md/array_state.  If that contains
'clean' or 'inactive' then there is no point opening the device.
Otherwise there might be a point, and the race would be a lot harder
to lose.

I guess it is time for me to learn about udev config files...

NeilBrown
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