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From: "Hunt, David" <david.hunt@intel.com>
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Date: Wed, 7 Jun 2017 11:28:49 +0100
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Subject: Re: [dpdk-dev] [PATCH v2 1/2] mk: allow use of environment var for
	make config
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Hi Shreyansh,


On 7/6/2017 10:36 AM, Shreyansh Jain wrote:
> Hello David,
>
> On Wednesday 07 June 2017 02:09 PM, Hunt, David wrote:
>> Shreyansh,
>>
>>      I found an issue (or two) with this part of the patch, and have 
>> a proposed solution.
>>
>> 1. RTE_TARGET originally had a different meaning. It was used for 
>> making examples, specifying the target directory of where the SDK was 
>> built. It's not good to re-purpose this for something else, as I'm 
>> doing in this patch. (even though I'm not sure that variable is 
>> suitably named in the first place, but that's a different issue).
>
> Even I didn't realize this until you highlighted here.
>
>> 2. If we set RTE_TARGET on the environment, we will break the 'make 
>> -C examples/<app>', unless we set RTE_TARGET to be something else 
>> (i.e. 'make -C examples/<app> RTE_TARGET=build'). One value for 
>> making DPDK, and another for building examples. It's confusing to the 
>> user.
>
> Agree about re-using RTE_TARGET is breaking existing assumption about
> its use.
>
>>
>> An alternative patch would be as follows:
>>
>>   RTE_CONFIG_TEMPLATE :=
>>   ifdef T
>> *-ifeq ("$(origin T)", "command line")*
>>   RTE_CONFIG_TEMPLATE := $(RTE_SRCDIR)/config/defconfig_$(T)
>> *-endif**
>> *endif
>>   export RTE_CONFIG_TEMPLATE
> So, that would mean, user would do either of the following:
>
> make T=<template> config
>
> or
>
> export T=<template>
> make config
>
> Is that correct? (I tried it and it seems to be working fine)
> First method is same as today. For the second, I am just skeptical
> whether we should use such a small identifier ("T") or we have a new
> RTE_TEMPLATE.
>
> Either way, I am OK. [export T=<template>] looks fine to me - in fact,
> on a second though, IMO, if T=<template> is provided as command line, 
> it should also be acceptable as env variable.
>

I did a quick poll here in the office and people feel that 'T' is too 
short for an environment variable. RTE_TEMPLATE would be preferred, and 
it's a sensible choice that does not conflict with RTE_TARGET.

So if we use RTE_TEMPLATE, we'd also have to put in a couple of lines 
for the "make install" case, but it's still a small enough patch:

diff --git a/mk/rte.sdkinstall.mk b/mk/rte.sdkinstall.mk
index dbac2a2..a464b01 100644
--- a/mk/rte.sdkinstall.mk
+++ b/mk/rte.sdkinstall.mk
@@ -47,6 +47,10 @@ ifneq ($(MAKECMDGOALS),pre_install)
  include $(RTE_SDK)/mk/rte.vars.mk
  endif

*+ifndef T**
**+T := $(RTE_TEMPLATE)**
**+endif**
* ifdef T # defaults with T= will install an almost flat staging tree
  export prefix ?=
  kerneldir   ?= $(prefix)/kmod


diff --git a/mk/rte.sdkroot.mk b/mk/rte.sdkroot.mk
index 076a2d7..0b71a4e 100644
--- a/mk/rte.sdkroot.mk
+++ b/mk/rte.sdkroot.mk
@@ -63,6 +63,8 @@ ifdef T
  ifeq ("$(origin T)", "command line")
  RTE_CONFIG_TEMPLATE := $(RTE_SRCDIR)/config/defconfig_$(T)
  endif
*+else**
**+RTE_CONFIG_TEMPLATE := $(RTE_SRCDIR)/config/defconfig_$(RTE_TEMPLATE)**
* endif
  export RTE_CONFIG_TEMPLATE

So if T is provided on the command line, it takes priority.
If that seems reasonable to you, I'll push up a v3. :)

Regards,
Dave.