[CentOS] Linux vs Windows Drivers

Bit bit2300 at gmail.com
Wed Dec 26 22:01:54 UTC 2007


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?

Thanks!
bit



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