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Date: Thu, 20 Sep 2012 06:15:54 +0400
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Maksim Yevmenkin <maksim.yevmenkin@gmail.com>
Message-ID: <20120920021554.GP85604@FreeBSD.org>
References: <CAFPOs6oCot3Bt8S9KUoC-cELw5reP5jmwWnwxS21h=Zq3Q0d-A@mail.gmail.com>
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Cc: FreeBSD Current <freebsd-current@FreeBSD.org>,
	Scott Long <scottl@FreeBSD.org>
Subject: Re: [RFC] how to get real ifi_baudrate from network interface
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On Wed, Sep 19, 2012 at 02:16:17PM -0700, Maksim Yevmenkin wrote:
M> hello,
M> 
M> for sometime now i've been repeatedly annoyed by the fact that 10G
M> interfaces lie about their ifi_baudrate. i would like to propose
M> simple (hopefuly) change to address this.
M> 
M> quick summary of the problem:
M> 
M> struct if_data {
M> ...
M>         u_char  ifi_spare_char1;        /* spare byte */
M>         u_char  ifi_spare_char2;        /* spare byte */
M> ...
M>         u_long  ifi_baudrate;           /* linespeed */
M> ...
M> };
M> 
M> as you can see ifi_baudrate is an u_long which is an arch specific
M> type. on 32-bit arch it does not have enough bits to hold 10G line
M> speed value (in bits per second)
M> 
M> proposal
M> 
M> we reuse one of the ifi_spare_char1 or ifi_spare_char2 bytes and
M> re-purpose it as power factor to be applied to ifi_baudrate, i.e.
M> 
M> real_ifi_baudrate = ifi_baudrate * 10 ** ifi_spare_char1
M> 
M> obviously, 10G nic drivers will have to set ifi_spare_char1 to
M> appropriate value, but it should not be a big deal. also, legacy tools
M> that do not know about ifi_spare_char1 would continue to report
M> "wrong" ifi_baudrate as they used to.
M> 
M> any objections?

IMO, this is way to go for stable branches. In head it'll be better just
have uint64_t without any crutches.

-- 
Totus tuus, Glebius.