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From:   David Howells <dhowells@redhat.com>
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To:     Randy Dunlap <rdunlap@infradead.org>
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        Casey Schaufler <casey@schaufler-ca.com>,
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Subject: Re: [PATCH 2/6] Adjust watch_queue documentation to mention mount and superblock watches. [ver #5]
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Date:   Mon, 01 Jul 2019 09:52:50 +0100
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Randy Dunlap <rdunlap@infradead.org> wrote:

> I'm having a little trouble parsing that sentence.
> Could you clarify it or maybe rewrite/modify it?
> Thanks.

How about:

  * ``info_filter`` and ``info_mask`` act as a filter on the info field of the
    notification record.  The notification is only written into the buffer if::

	(watch.info & info_mask) == info_filter

    This could be used, for example, to ignore events that are not exactly on
    the watched point in a mount tree by specifying NOTIFY_MOUNT_IN_SUBTREE
    must not be set, e.g.::

	{
		.type = WATCH_TYPE_MOUNT_NOTIFY,
		.info_filter = 0,
		.info_mask = NOTIFY_MOUNT_IN_SUBTREE,
		.subtype_filter = ...,
	}

    as an event would be only permissible with this filter if::

    	(watch.info & NOTIFY_MOUNT_IN_SUBTREE) == 0

David