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Date:      Tue, 4 Jan 2011 09:55:31 -0700
From:      Scott Long <scottl@samsco.org>
To:        Poul-Henning Kamp <phk@phk.freebsd.dk>
Cc:        arch@freebsd.org, Alfred Perlstein <alfred@freebsd.org>, Garrett Cooper <gcooper@freebsd.org>
Subject:   Re: Linux kernel compatability 
Message-ID:  <EDC4D6B1-7D67-4E22-90B7-5A91C916AB56@samsco.org>
In-Reply-To: <85271.1294128867@critter.freebsd.dk>
References:  <85271.1294128867@critter.freebsd.dk>

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On Jan 4, 2011, at 1:14 AM, Poul-Henning Kamp wrote:
> In message <alpine.BSF.2.00.1101031333400.1450@desktop>, Jeff Roberson =
writes:
>=20
>> Also, linux likes to change things very rapidly.  Not to mention a =
lot of=20
>> their APIs go against the grain on BSD and we would not find them=20
>> aesthetically or architecturally pleasing.
>=20
> Absolutely.
>=20
> But we, as a project, must also weigh the cost of our sensibilities
> and preferences, against how much work we must expend to uphold them.
>=20

I have mixed feelings about Jeff's shim layer.  On the plus side, I =
think that there's value to emulation without copying.  On the negative =
side, I agree with ALexander's concern that it's a large chuck of code =
to be maintained.  Emulation isn't a bad thing.  It allows IHV's as well =
as individual developers to take baby steps with getting familiar with =
FreeBSD.    It lowers the barrier to entry.  The ones who aren't going =
to put in the effort to making the leap from "emulation" to "native" =
likely aren't going to take the leap with going from "nothing" to =
"native" either.  I understand the argument that it will coddle people =
into using just the emulation and not the native interfaces, thus =
degrading the value of the native interfaces.  I'm just not sure how =
much I believe that in my experience.

I recall years ago Matt Jacob mentioning with some concern that the =
project seemed to be aimed at creating a "FreeSolaris" of sorts; many of =
the architectural decisions seemed to be based on the argument that =
Solaris was doing it, so FreeBSD should too.  That's fine, and there's a =
certain amount of comfort in following an arguably decent architectural =
standard like Solaris, though I understand what I believed to be Matt's =
point about retaining some identity and exploring new paths rather than =
just following old paths.

In my not so humble opinion, Linux is not an architectural model to be =
envied or copied, regardless of how pragmatic it might seem.  Sure, =
gratuitous differences can be argued against, but there are a lot of =
fundamental architectural things that linux succeed at purely by brute =
force of will, and nothing more.  FreeBSD should be careful to not envy =
that model.  I think that there's a lot less value in both the long and =
short terms in a "FreeLinux" than in a "FreeSolaris", and neither are =
all that good in the long term.

Having an emulation gives people a lower barrier to entry and some =
stepping stones to getting comfortable with FreeBSD.  It gives them a =
series of achievable goals with costs and benefits at each step that can =
be weighed.  Aiming at simply evolving the native interfaces to be like =
linux simply means that FreeBSD becomes a poor copy of linux with =
nothing else under the surface to set it apart or create an attraction.

Scott




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