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From: Philipp Reisner <philipp.reisner@linbit.com>
To: Nick Wang <nwang@suse.com>
Date: Fri, 31 Jul 2015 14:50:53 +0200
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Cc: Lars Ellenberg <lars.ellenberg@linbit.com>, linux-kernel@vger.kernel.org,
	drbd-dev@lists.linbit.com
Subject: Re: [Drbd-dev] [Patch v2 02/10] drbd: Add option zap_devices to
	new-current-uuid
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Hi Nick,

When introducing new fields alsways mark them as optional. Otherwise
a new kernel/module code would refuse netlink messages from older
drbd-utils:

> +	__flg_field(2, DRBD_GENLA_F_MANDATORY, zap_devices)

__flg_field(2, /* OPTIONAL */ 0, zap_devices)

best regards,
 Phil