[lttng-dev] [PATCH lttng-modules] Fix: disable kvm probe if lapic.h isn't found

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

----- On Jul 24, 2015, at 2:18 PM, Chris J Arges chris.j.arges at canonical.com wrote:

> In a typical distribution if just linux-headers is installed, lapic.h will
> not be installed. We should check if that file exists and not build the module.

Hi Chris,

Although this patch looks technically correct, I'd like to understand
how you triggered this issue in the first place.

If we look at this Makefile, we skip building KVM probes altogether
if neither $(srctree)/virt/kvm/iodev.h nor $(srctree)/include/kvm/iodev.h
are found. AFAIU, none of those headers are installed as linux-headers.

Which of those headers are found in your distribution headers ? Is it
due to a modification specific to Ubuntu or is it something that
appears in mainline kernel ?

Thanks!

Mathieu

> 
> Signed-off-by: Chris J Arges <chris.j.arges at canonical.com>
> ---
> probes/Makefile | 5 +++++
> 1 file changed, 5 insertions(+)
> 
> diff --git a/probes/Makefile b/probes/Makefile
> index 0314a5e..cc4c352 100644
> --- a/probes/Makefile
> +++ b/probes/Makefile
> @@ -25,6 +25,8 @@ obj-m += lttng-probe-statedump.o
> ifneq ($(CONFIG_KVM),)
> obj-m += lttng-probe-kvm.o
> ifneq ($(CONFIG_X86),)
> +kvm_dep_lapic = $(srctree)/arch/x86/kvm/lapic.h
> +ifneq ($(wildcard $(kvm_dep_lapic)),)
> kvm_dep = $(srctree)/virt/kvm/iodev.h $(srctree)/include/kvm/iodev.h
> ifneq ($(wildcard $(kvm_dep)),)
> CFLAGS_lttng-probe-kvm-x86.o += -I$(srctree)/virt/kvm
> @@ -40,6 +42,9 @@ obj-m +=  $(shell \
> else
> $(warning File $(kvm_dep) not found. Probe "kvm" x86-specific is disabled. Use
> full kernel source tree to enable it.)
> endif
> +else
> +$(warning File $(kvm_dep_lapic) not found. Probe "kvm" x86-specific is
> disabled. Use full kernel source tree to enable it.)
> +endif
> endif
> endif
> 
> --
> 2.1.4
> 
> 
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com