A short digression on FOSS (Re: understanding speculative preallocation)

[Keith Keller]

On 2013-07-29, Eric Sandeen <sandeen at sandeen.net> wrote:
> On 7/28/13 11:57 PM, Keith Keller wrote:
>> 
>> The current stable kernel is 3.10.4.  Let's suppose that 3.10.5 comes
>> out tomorrow with some interesting patches to fs/xfs.  Is it possible
>> using dkms to build the 3.10.5 version of the xfs module for a running
>> 3.10.4 kernel?  
>
> "Probably / Maybe"
>
> It really depends on what changed from 3.10.4 to 3.10.5, but odds are,
> kernel interfaces did not change, so - probably fine.  If not, you
> get to keep all the pieces, etc.

Sure.  :)

>> And if so, is there a way for the module to report its
>> own version?
>
> Say it with me: there is no xfs module version.  :)

Well, wouldn't it be the same as the original kernel from which the code
was ripped?  So in the above hypothetical, one could say that the xfs
"version" is 3.10.5.  It's not *exactly*, of course, but if I were to
say "I'm running kernel 3.10.4 with xfs built from 3.10.5 using DKMS"
you'd probably know what I meant.  You might then choose not to answer
questions because I've gone too far off the reservation.

Or, maybe, a different way of saying this is that the XFS version always
matches the kernel version it comes from.  Then if you use code from one
kernel version in a different version it's at your own risk; one of the
consequences is that you need to document this discrepancy yourself.

> And taking kernel version X's xfs, and applying a bugfix patch, and
> rebuilding it against the same kernel headers should be fine.  Still
> a little wizardry, but not bad for a kernel-savvy person.

Is that all it takes to be considered "wizardry"?  Back In My Day (TM)
you had to mess with .config in order to get anything done!  ;-)

--keith

-- 
kkeller at wombat.san-francisco.ca.us