linux-kernel - Re: [PATCH net-next v1 0/7] net: extend ethtool link mode bitmaps to 48 bits

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Date:	Mon, 5 Jan 2015 10:16:35 -0800
From:	David Decotigny <ddecotig@...il.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Maciej Żenczykowski <zenczykowski@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Linux NetDev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Al Viro <viro@...iv.linux.org.uk>,
	Masatake YAMATO <yamato@...hat.com>, Xi Wang <xii@...gle.com>,
	Neil Horman <nhorman@...driver.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	Flavio Leitner <fbl@...hat.com>, Tom Gundersen <teg@...m.no>,
	Jiri Pirko <jiri@...nulli.us>,
	Vlad Yasevich <vyasevic@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Venkata Duvvuru <VenkatKumar.Duvvuru@...lex.com>,
	Govindarajulu Varadarajan <_govind@....com>
Subject: Re: [PATCH net-next v1 0/7] net: extend ethtool link mode bitmaps to
 48 bits

Thanks Ben, I will send an updated version.

About rejecting high bits in drivers that don't support them: a basic
fix (in a separate patch series) could be something like follows in
ethtool_set_settings callbacks:  if (ecmd->advertising_hi) return
-EINVAL; with comments. But I don't find it very nice. Or: allocate a
new net_device::priv_flags bit and ask net/core/ethtool.c to accept
high advertising bits only when this flag is set? Any preference/other
options?

Related: lately, each new class of link modes declared == 4 new bits
allocated. At current pace these 16 new bits buy us only 4 new
classes, ie. a little more than 5 years if I extrapolate from the
recent past. Is the longer term plan to create a new ethtool ioctl
command specialized in link modes with variable length masks? Or to
switch to a brand new netlink interface altogether and take advantage
of that to revisit the link mode reporting/configuration with variable
length masks?

On Sun, Jan 4, 2015 at 6:30 PM, Ben Hutchings <ben@...adent.org.uk> wrote:
> On Mon, 2015-01-05 at 01:34 +0100, Maciej Żenczykowski wrote:
>> >> I can send updates to other drivers, even though it's rather pointless
>> >> to update 1G drivers at this point for example. Please let me know,
>> >> but I'd prefer to do this in follow-up patches outside this first
>> >> patch series.
>> > [...]
>> >
>> > They should be changed to ensure they reject setting any of the high
>> > advertising flags, but it's not urgent.
>>
>> if old drivers advertised a get/set_bits function while new drivers
>> advertised a get/set_new_bits function,
>> you could not updated any old drivers, and simply take care of
>> rejecting invalid bits in core, by calling set_new_bits if provided,
>> if not, rejecting bad bits and calling set_bits if no bad bits were
>> set.
>
> We've never checked that the reserved fields are zero before, and I
> think there are still drivers that don't fully validate the existing 32
> bits.  So while I think drivers should fully validate the advertising
> flags, userland generally can't assume they do.  And therefore I don't
> think it's worth adding complexity to the ethtool core that only partly
> fixes this.
>
> Ben.
>
> --
> Ben Hutchings
> This sentence contradicts itself - no actually it doesn't.
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