Re: "blktrace: fix accounting ..." breaks lttng API in -stable trees

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On Fri, May 02, 2014 at 11:09:08AM -0700, Kamal Mostafa wrote:
> On Fri, 2014-05-02 at 13:30 -0400, gregkh wrote:
> > On Fri, May 02, 2014 at 10:07:33AM -0700, Kamal Mostafa wrote:
> > > Dirk Behme points out that this "Cc: stable" commit breaks the
> > > lttng-modules userspace API when applied to stable kernels.  Stable
> > > versions 3.2, 3.8, 3.11, and 3.13 (at least) have all queued it:
> > > 
> > >         af5040da01ef980670b3741b3e10733ee3e33566
> > >         blktrace: fix accounting of partially completed requests
> > > 
> > > 
> > > On Thu, 2014-05-01 at 10:28 +0200, Dirk Behme wrote:
> > > > [...] might break the build of the user space lttng-modules
> > > > (lttng-probe-block.c) due the the API change of
> > > > trace_block_rq_complete().
> > > 
> > > > [...] On the other hand, looking into the lttng-modules git
> > > > http://git.lttng.org/?p=lttng-modules.git;a=commitdiff;h=1c53e689434a6bdd7dc3f54c07bfb72750d1d24c
> > > > looks like this is the necessary user space adaption to the kernel 
> > > > change? So this looks like that lttng-modules expects a KERNEL_VERSION
> > > > >= (3,15,0) to have this commit?
> > > 
> > > 
> > > My inclination is that we probably need to revert/drop "af5040d
> > > blktrace: fix accounting..." from the stable kernels to unbreak the
> > > userspace API.
> > 
> > Then you will run into this issue with 3.15, when it is released.
> 
> No, I think "#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,15,0))" in the
> lttng-modules commit referenced above guards against that.  Apparently,
> lttng-modules expects to see the new API in >= 3.15 and the old API in
> the stable kernels.

Then that's an lttng issue, not a kernel community issue, sorry.

greg k-h
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