[CentOS] Linux vs Windows Drivers

[Johnny Hughes]

Bit wrote:
> Luciano Rocha wrote:
>> On Wed, Dec 26, 2007 at 04:01:22PM -0500, Bit wrote:
>>  
>>>  Luciano Rocha wrote:
>>>    
>>>> On Wed, Dec 26, 2007 at 12:48:52PM -0500, Bit wrote:
>>>>        
>>>>>  Thanks to both of you for the reply.  Good information, but that
>>>>> still  doesn't really answer my question.  I'm more interested in
>>>>> the technical  side of things.  What I really want to understand
>>>>> boils down to this:
>>>>>
>>>>>  Why is it that in Windows I can install ATI drivers once and never
>>>>> worry  about it again, while in Linux I may have to *reinstall* the
>>>>> drivers at a  later date after a system update to get my card
>>>>> working with them again?   Experience has proven to me that in
>>>>> Windows I can install the ATI drivers  once, leave those same
>>>>> drivers on there for eternity, update the system over  and over
>>>>> with Automatic Updates, and never worry about it breaking my video 
>>>>> card.  In Linux, every time I see a kernel update, I've learned to
>>>>> be braced  for impact and just be ready with my ATI drivers to
>>>>> reinstall to get my card  working again.  I've never understood
>>>>> this.  I'd like a technical  explanation for why this is so.
>>>>>
>>>>>             
>>>> Linux doesn't have a stable ABI (for drivers, userland is a different
>>>> thing), but Windows does.
>>>>
>>>> That means that drivers compiled for your kernel today may not install
>>>> on newer (or older) kernels. You'll have to recompile it. Also, changes
>>>> like support for more than 4GB, how the lower 4GB is split,
>>>> architecture
>>>> options, gcc version, function calling convections, etc., creates
>>>> dependencies that have to be met by the binary driver.
>>>>
>>>> Windows guarantees that the exposed interface doesn't change, so
>>>> there's
>>>> no need to recompile things if something internal changes.
>>>>
>>>> But Linux doesn't even have a stable API, so the module may not compile
>>>> on your newer kernels.
>>>>
>>>> Please see Documentation/stable_api_nonsense.txt, in the kernel
>>>> sources,
>>>> or online at:
>>>> <http://scienceblogs.com/gregladen/2007/12/linux_stable_api_vs_not.php>
>>>>
>>>> Note that without a stable API, there is no change of a stable ABI.
>>>>
>>>>         
>>>  Luciano, thank you very much.  I read your post, the link you
>>> provided, and  a few other things from that link, and I at least
>>> understood enough to  realize that it answers my question.  I think I
>>> *kind of* get it now.
>>>
>>>  I think understanding the answer to my question really revolves
>>> around  understanding an API and an ABI.  Would you please read the
>>> following and  let me know if I at least get the gist of what these
>>> two things are?
>>>     
>>
>> FYI, when in doubt about these acronyms, search for "define: ABI", for
>> instance, in google.
>>
>>  
>>>  An API influences what your source code will look like.  If they
>>> change the  Linux kernel API, then you may need to make changes to
>>> your source code such  as making "myLinuxKernelAPIFunctionCall(
>>> myparam1, myparam2 )" look  something more like
>>> "myUpdatedLinuxKernelAPIFunctionCall( myparam1 )" in  order to even
>>> make your code compile.
>>>     
>>
>> Yes, but also more important things. Like changing the use of semaphores
>> to mutexes, when appropriate (they "lock" something, mutexes can have
>> only one accessing the something at once, while semaphores can have N
>> accessing); changing the way stuff is exported to userland (sysfs,
>> configfs, debugfs, relayfs, procfs); etc..
>>
>>  
>>>  The ABI is the interface between a compiled binary kernel module and
>>> the  kernel.  It determines if an already compiled binary will
>>> properly interface  with the kernel and run.  If the ABI changes and
>>> you find your kernel module  won't run properly, you just need to
>>> recompile from source to get a kernel  module that will run. 
>>> Hopefully the API hasn't changed and you won't need  to change your
>>> source code to make it recompile...
>>>     
>>
>> Yes, that's it. The compiled modules include the dependency info, so
>> that you won't be able to insert it in another kernel:
>> $ modinfo ext2.ko
>> filename:       ext2.ko
>> license:        GPL
>> description:    Second Extended Filesystem
>> author:         Remy Card and others
>> depends:
>> vermagic:       2.6.23.12lcfs1 preempt mod_unload PENTIUM4 4KSTACKS
>>
>>  
>>>  BOTH kinds of changes happen with some degree of frequency in Linux.
>>>     
>>
>> Yes. Due to the nature of the kernel (open-source, GPL), and the current
>> policy, changes occur *very* frequently, especially in the 2.6.x series.
>>
>>  
>>>  Did I get at least this much right?
>>>     
>>
>> I think you're doing fine. Note that this state of affairs is more due
>> to how the kernel people work/philosophy, than due to technical
>> limitations, as Les Mikesell pointed out.
>>
>> Anyway, nifty things have come from this development method in the
>> latest Linux kernels.
>>
>> Also, there are some stable apis/abis: userland driver (for simple
>> devices, no dma is possible, for instance), and userland access to usb
>> devices (mostly used for printers, scanners and non-standard usb memory
>> sticks/mp3 players).
>>
>>   
> Thank you again for your help!  You've given me a place to really get
> started and this doesn't seem quite so mysterious to me anymore.  I have
> one last related burning question for now that I was hoping you might be
> able to answer.
> 
> ATI drivers are proprietary and closed-source.  So, for example, on my
> current desktop, I download the Linux drivers for my card from the link
> below and run the installer as per their instructions.
> http://ati.amd.com/support/drivers/linux/linux-radeon.html
> 
> It's doing *something* to make a kernel module that will insert into and
> work with my current running kernel.  At one time, I thought that it was
> compiling a module from source code, probably by invoking make, in much
> the same way I might download and install any open-source software in
> Linux from a tarball.
> 
> However, I realized that this doesn't make sense since ATI's drivers are
> proprietary and closed-source.  So the installer I download can't
> possibly be compiling anything from source code, because that would mean
> I could almost certainly read the source code, which they don't want. 
> Which leaves me wondering what the installer is really doing.  Any ideas?
> 

It is compiling a module from kernel source code  ...  part of the
process also LINKS into PRE compiled object files (also known a .o
files) and /or shared object files (also known as .so files).

ATI (and nvidia) provide pre-compiled .o files to link to ... without
providing the source code to build the .o files.

The newer ATI drivers are really open source, so they provide the source
code to build the .o files.


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