From: Neil Brown <neilb@suse.de>
To: Kay Sievers <kay.sievers@vrfy.org>
Date: Thu, 9 Nov 2006 11:17:57 +1100
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Cc: Greg KH <gregkh@suse.de>, Andrew Morton <akpm@osdl.org>,
       linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 001 of 6] md: Send online/offline uevents when an md
	array starts/stops.
In-Reply-To: message from Kay Sievers on Wednesday November 8
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On Wednesday November 8, kay.sievers@vrfy.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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