netdev - confusing comment, explanation of @IFF

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Message-ID: <alpine.LFD.2.21.1808260410530.31293@localhost.localdomain>
Date:   Sun, 26 Aug 2018 04:13:25 -0400 (EDT)
From:   "Robert P. J. Day" <rpjday@...shcourse.ca>
To:     Linux kernel netdev mailing list <netdev@...r.kernel.org>
Subject: confusing comment, explanation of @IFF_RUNNING in if.h

  more annoying pedantry ... from include/uapi/linux/if.h:

    * @IFF_RUNNING: interface RFC2863 OPER_UP. Volatile.

however, both the code in net/core/dev.c:

/**
 *      netif_oper_up - test if device is operational
 *      @dev: network device
 *
 * Check if carrier is operational
 */
static inline bool netif_oper_up(const struct net_device *dev)
{
        return (dev->operstate == IF_OPER_UP ||
                dev->operstate == IF_OPER_UNKNOWN /* backward compat */);
}

and the explanation in operstates.txt:

  ifinfomsg::if_flags & IFF_RUNNING:
    Interface is in RFC2863 operational state UP or UNKNOWN.

suggests IFF_RUNNING represents *either* of the operational states UP
or UNKNOWN, not just UP as the comment in if.h claims. is this
misleading? or is this a deliberate explanation somehow taking into
account that the UNKNOWN state is for backward compatibility (whatever
that means)?

  i ask since, in my testing, when the interface should have been up,
the attribute file "operstate" for that interface showed "unknown",
and i wondered how worried i should be about that.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                  http://crashcourse.ca/dokuwiki

Twitter:                                       http://twitter.com/rpjday
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