Embedded Linux Overview: Free Beer, Free Speech

An anonymous reader writes "Never one to have his thirst for 'free beer' quenched, LinuxDevices.com contributing editor Kevin Dankwardt sets off on a quest to determine just how much freely downloadable embedded Linux software flows from the taps of commercial embedded Linux vendors' websites -- and discovers that there's a lot more available than you might realize. Read Dankwardt's guide to 'free beer' (well, uhm, free embedded Linux, that is)."

This is worth noting re. GPL

[renehollan]

From the article (and perhaps I am stretching fair use doctrine a bit by copying two whole paragraphs, but I wanted to get context clear):

Without going into a dissertation on GPL, it should be noted the GPL expects companies developing or selling products based on (or containing) embedded Linux make source code to the GPL components used in their products available to their end customers who request it. Therefore, as a consequence of GPL, if you need kernel sources for some specific processor, you ought to be able to buy a device known to be based on that processor, that uses embedded Linux, and then request and obtain source to that processor's kernel from the maker (or supplier) of that device.

Indeed, some device and system manufacturers do make sources to the embedded Linux kernel and other open source software used in their products freely available (by some other means) to their end customers. Unfortunately, however, we have found that many device and system vendors appear to consider themselves "above the law" when it comes to the GPL's source code obligations. For example, the author recently purchased an embedded Linux powered device and, when he asked the vendor's support person how to obtain a copy of the Linux they used, was politely informed that their product uses "a proprietary version of Linux." Additionally, some developers of kernel loadable module code, such as for device drivers, believe that by packaging their code as a loadable module it need not be released under the GPL. Thus, you might not be able to obtain source to some of the Linux code in your system even if you are one of their customers.

Am I the only one who sees this as a serious breach of the GPL and an affront and insult to the free software community?

Re:This is worth noting re. GPL

[phyxeld]

I don't understand why he would make such a serious allegation...

For example, the author recently purchased an embedded Linux powered device and, when he asked the vendor's support person how to obtain a copy of the Linux they used, was politely informed that their product uses "a proprietary version of Linux."

...and yet not tell the community which vendor he's speaking of! If what he says is true, and they're shipping a modified kernel and witholding the source, they are definitely in violation. So who

Re:This is worth noting re. GPL

[renehollan]

don't understand why he would make such a serious allegation...

... perhaps precisely because it is a serious allegation and the author is not a lawyer.

Though I agree that stating the facts without an opinion and identifying the supplier would probably be safe, without mentioning why this is done (i.e. the possibility of a GPL violation), the point would probably be lost on many readers.

Re:This is worth noting re. GPL

[Samrobb]

Additionally, some developers of kernel loadable module code, such as for device drivers, believe that by packaging their code as a loadable module it need not be released under the GPL.

Hmm? I thought that this type of construct was specifically allowed. There are many companies who release proprietary code as loadable kernel modules - video drivers, for example. A quick Google shows that binary-only lkm's are permissible [lwn.net], though apparently there is some effort being made to clearly define what "permi

Re:This is worth noting re. GPL

[renehollan]

Yes, this is explicitly permitted by the license on the Linux kernel, but, IIRC, there is also an option honoured by the kernel that allows a module to indicate that it should not be loaded unless all other loaded modules are GPL.

So, legally you are correct, but the practice is viewed with some disdain, particularly when a "toy" GPL application is provided, making it look like the code is free, yet it relies on a kernel module that does the real work.

Re:This is worth noting re. GPL

[Samrobb]

Hmm... interesting. Is this type of behavior allowable under the GPL? It seems to be an additional restriction on how the software can be used. At first glance, I would think there's no difference between saying "You may not use this kernel module with non-GPL code" and "You may not use this kernel module unless you are a customer of company X".

Nevermind that, if a kernel module is under the GPL, there's nothing preventing me from modifying it to run without these restrictions, and then distributing the

Re:This is worth noting re. GPL

[renehollan]

Hmm... interesting. Is this type of behavior allowable under the GPL?

In a word, NO!

...and I'm sorry if I gave that impression. What you miss (and I failed to make clear) is the the Linux kernel is not licensed under the GPL. It is licensed under the GPL with a specific exception for kernel modules.

Now, there is nothing wrong with this, as Linus Torvalds can license his code any way he likes, and contributors have to accept that license for their contributions to be redistributed. Since some contributers prefer a pure GPL position, for political reasons, the means are there for their modules to check, at run-time, if any other non-GPL code has been dynamically linked in, at least that is my understanding. I don't know if this technique can apply to any contributed kernel code, but I see no reason why it couldn't in practice.

It is my understanding that RMS is very upset about this particular exception, but that should come as no surprise. It has led to production of non-free drivers within kernel modules with minimal "free" applications under the misleading notion that the code (all of it) is free. I'm told that NVidia does this with some of their video drivers, and RMS considers that very unfriendly, to the point of NVidia being hostile to the free software community (Disclaimer: I work for ATI, a competitor of NVidia, but these comments are entirely mine and not representative of any position ATI might take).

But, the fact remains, proprietary kernel modules or not, if you distribute binaries of the Linux kernel, even if unmodified (your mods being entirely in kernel modules), the GPL obliges you to either (a) distribute the source, (b) offer the source to anyone who asks (not just the recipient of your binaries) and has received the binaries, or (c) point them to a well-known location where they can be found. Option (c) is only available for non-commercial redistributors.

Contrary to popular belief, this does mean that a pointer to an FTP site you maintain is not sufficient complience unless that's where the binaries came from -- that is you can't ship CDs of binaries with a pointer to an FTP site as the only means of obtaining source, though it is perfectly acceptable to do this as an alternate means.

Now, the GPL strikes me as a little vague when it comes to inter-process communication between cooperating processes as part of a whole. Tom Christiansen's "GPL-freeing" socket wrapper around readline() is an example of it. While it may be legally complient with the GPL (though I am not a lawyer and you should seek specific advice from your legal council), it is generally viewed as deceitful and unfriendly by many.

Re:This is worth noting re. GPL

[Samrobb]

What you miss (and I failed to make clear) is the the Linux kernel is not licensed under the GPL. It is licensed under the GPL with a specific exception for kernel modules.

You're right, of course - that's easy to forget. Thanks for reminding me.

Re:This is worth noting re. GPL

[renehollan]

I would think there's no difference between saying "You may not use this kernel module with non-GPL code" and "You may not use this kernel module unless you are a customer of company X".

Oh, but there is a world of difference! And, an error in your logic.

First, the GPL does not address use, except to the extent that use, including redistribution is restricted according to the manner of redustribution: If you do not redistribute, you can use GPL code any way you like. If you do redistribute, you an only u

Re:This is worth noting re. GPL

[Captain Large Face]

Too true -- I use the nvidia module as a driver for my graphics card. You'll get a warning about tainting the kernel, but there's nothing there to break the GPL, as I understand it...

Re:This is worth noting re. GPL

[valshaq]

If you had read that article instead of just posting it, you would have noticed that binary-only modules are illegal and even Linus agrees to that nowadays:

This is, of course, an explicit shot across the bow of anybody who distributes proprietary kernel modules. Linus, then, sent out his current view on binary-only modules:

There is NOTHING in the kernel license that allows modules to be non-GPL'd.

(cited from that very article :-)

Re:This is worth noting re. GPL

[renehollan]

Perhaps you are citing a different article. The text you cited appears nowhere in the article in question.

Since your claim goes against common wisdon, I would very much like to see a cite.

Re:This is worth noting re. GPL

[valshaq]

http://lwn.net/Articles/13398/ (fifth/sixth paragraph) And no, it's not illegal to MAKE such a module but to distribute it ;-)

Re:This is worth noting re. GPL

[renehollan]

Your quote was from a different article [lwn.net]. This thread was referring to this [linuxdevices.com] article. Still the points you raise are worth respondong to.

First, you quoted out of context. Expanding the quote a bit:

This situation has thus always been a little unstable. It came up again in recent times when Christoph Hellwig posted a patch which explicitly made the Linux Security Module functionality available only to modules licensed under the GPL. People were, says Christoph, using the LSM hooks to change the behavior of

Re:This is worth noting re. GPL

[valshaq]

Well, the problem that I see is:

Linus didn't care too strictly about licenses and copyright in the past. So, it would be very difficult to enforce the copyright on the kernel as a whole (that's why Christoph Hellwig had to invent that technical solution for his own modules).

Defacto practice just sucks: nvidia (or ati or whoever) creates that cool hardware we all need to have and makes it almost impossible to write free and legal drivers for it. That's why binary-only drivers are so dangerous and I'm so ha

Re:This is worth noting re. GPL

[RAMMS+EIN]

It's a grey area. If they modify parts of the Linux kernel and distribute it, then they have to make available the sources no their changes under GPL. If they add their own applications and/or libraries, they have no obligation to do so (although they still need to make sure the sources to the version of Linux they are distribution are available).

But what if they write device drivers? They are part of the kernel in a way, yet there are many binary-only modules out there, and Linus allows them. Thus, there

requirement?

[SHEENmaster]

I'll be distributing a program for many platforms, and a feature of the program's disc is that it can boot Linux to run the app.

1. I am using a stock SELinux 2.4.20 kernel, do I need to redistribute the source?
1a. Would a kernel configuration be acceptable?

2. Most of the apps included for Linux bootability are also stock, do I need to redistribute their source?

Re:requirement?

[Anonymous Coward]

You don't need to _redistribute_ the source, but you do have to make it available to those who request it (free of encumberances).

A tarred-up copy of SELinux + other application source code is sufficient.

Of course, a kernel config and any custom code must be disclosed as well.

[ Ideally, a person should be able to take the source code you provide and build the system that you distribute in binary form. ]

Re:requirement?

[fizbin]

Furthermore, there's nothing that says you can't be fairly compensated for your time in putting the source on CD and mailing it (just be sure to obey clause 3b of the GPL - you can't include the administrative overhead of keeping track of the source in your cost for producing a source CD)

Were I an embedded developer, here's what I'd do:
1) Read the GPL [gnu.org]. It's not that long, and as license go is very, very readable.
2) Place a "GPL compliance" notice in the printed documentation (along with any other required