netdev - Re: [PATCH net-next v3 03/17] net: ethtool: add new ETHTOOL

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Date:	Tue, 1 Dec 2015 22:00:58 -0800
From:	David Decotigny <ddecotig@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	Amir Vadai <amirv@...lanox.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	linux-mips@...ux-mips.org, fcoe-devel@...n-fcoe.org,
	Eric Dumazet <edumazet@...gle.com>,
	Eugenia Emantayev <eugenia@...lanox.co.il>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Ido Shamay <idos@...lanox.com>, Joe Perches <joe@...ches.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Govindarajulu Varadarajan <_govind@....com>,
	Venkata Duvvuru <VenkatKumar.Duvvuru@...lex.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Eyal Perry <eyalpe@...lanox.com>,
	Pravin B Shelar <pshelar@...ira.com>,
	Ed Swierk <eswierk@...portsystems.com>,
	robert.w.love@...el.com,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Yuval.Mintz@...gic.com
Subject: Re: [PATCH net-next v3 03/17] net: ethtool: add new
 ETHTOOL_GSETTINGS/SSETTINGS API

Hello,

There is a set of conversion routines ulong[]<->u32[] to address this
32/64-bit compat issue. Using a u32-based bitmap would require drivers
to handle the u32 bitmaps themselves, this might be confusing,
considering there is a standard bitmap api; and might be error-prone
as well. Plus there is %*pb[l] format that's very helpful for
debugging. That's why I preferred to handle the relative complexity of
u32 bitmaps with the CPP conditionals in the non-driver code that
handles the user/kernel interactions, and drivers can use the standard
bitmap api transparently.

I was currently moving/rewriting the u32/ulong conversion code to
bitmap.{c,h} as Ben Hutchings was suggesting, which should hopefully
make the code more digestible; and could possibly be used for other
user/kernel interfaces. How about I send an updated version with this
solution, and if it's still not right, I'll revisit with either u32[]
everywhere or fixed-size bitmap instead of variable-size as here? Or
maybe another option would be to implement a new u32[]
bitmap_u32.{c,h} api, possibly using a set of macro tricks to share
code with bitmap.{c,h}?

On Tue, Dec 1, 2015 at 7:13 PM, David Miller <davem@...emloft.net> wrote:
> From: David Decotigny <ddecotig@...il.com>
> Date: Mon, 30 Nov 2015 14:05:41 -0800
>
>> This patch defines a new ETHTOOL_GSETTINGS/SSETTINGS API, handled by
>> the new get_ksettings/set_ksettings callbacks. This API provides
>> support for most legacy ethtool_cmd fields, adds support for larger
>> link mode masks (up to 4064 bits, variable length), and removes
>> ethtool_cmd deprecated fields (transceiver/maxrxpkt/maxtxpkt).
>
> Please do not define the mask using a non-fixed type.  I know it makes
> it easier to use the various bitmap helper routines if you use 'long',
> but here it is clearly superior to use "u32" for the bitmap type and
> do the bit operations by hand if necessary.
>
> Otherwise you have to have all of this ulong size CPP conditional code
> which is incredibly ugly.
>
> Furthermore you have to use fixed sized types anyways so that we don't
> need compat code to deal with 32-bit userspace applications making
> these ethtool calls into a 64-bit kernel.
>
> THanks.
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