why conditional assignment of DEPLOY_DIR_IMAGE in bitbake.conf?

why conditional assignment of DEPLOY_DIR_IMAGE in bitbake.conf?

[Robert P. J. Day]

  quite possibly another silly question, but i'm perusing poky's
version of bitbake.conf and i see this:

DEPLOY_DIR ?= "${TMPDIR}/deploy"
DEPLOY_DIR_TAR = "${DEPLOY_DIR}/tar"
DEPLOY_DIR_IPK = "${DEPLOY_DIR}/ipk"
DEPLOY_DIR_RPM = "${DEPLOY_DIR}/rpm"
DEPLOY_DIR_DEB = "${DEPLOY_DIR}/deb"
DEPLOY_DIR_IMAGE ?= "${DEPLOY_DIR}/images/${MACHINE}"
DEPLOY_DIR_TOOLS = "${DEPLOY_DIR}/tools"

  now, what is the value of using "?=" to set DEPLOY_DIR_IMAGE, rather
than just "=". i know what "?=" represents, but i normally expect to
see it in a context where someone might have set it earlier to some
other value, but this is in bitbake.conf, before any of the "include"
or "require" directives to pull in any of the other .conf files. so in
the midst of all those other DEPLOY_DIR_* hard assignments, why is the
images directory a conditional install?

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

Re: why conditional assignment of DEPLOY_DIR_IMAGE in bitbake.conf?

[Christopher Larson]

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On Tue, Jul 22, 2014 at 9:36 AM, Robert P. J. Day <rpjday@crashcourse.ca>
wrote:

>   quite possibly another silly question, but i'm perusing poky's
> version of bitbake.conf and i see this:
>
> DEPLOY_DIR ?= "${TMPDIR}/deploy"
> DEPLOY_DIR_TAR = "${DEPLOY_DIR}/tar"
> DEPLOY_DIR_IPK = "${DEPLOY_DIR}/ipk"
> DEPLOY_DIR_RPM = "${DEPLOY_DIR}/rpm"
> DEPLOY_DIR_DEB = "${DEPLOY_DIR}/deb"
> DEPLOY_DIR_IMAGE ?= "${DEPLOY_DIR}/images/${MACHINE}"
> DEPLOY_DIR_TOOLS = "${DEPLOY_DIR}/tools"
>
>   now, what is the value of using "?=" to set DEPLOY_DIR_IMAGE, rather
> than just "=". i know what "?=" represents, but i normally expect to
> see it in a context where someone might have set it earlier to some
> other value, but this is in bitbake.conf, before any of the "include"
> or "require" directives to pull in any of the other .conf files. so in
> the midst of all those other DEPLOY_DIR_* hard assignments, why is the
> images directory a conditional install?
>

s/install/define/

If there's a ?= done before any includes in bitbake.conf, either its
position in the file has changed, or it's set that way to allow the user to
add those variables to the env whitelist and set them in the environment,
as the env is set before bitbake.conf is parsed.
-- 
Christopher Larson
clarson at kergoth dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics

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Re: why conditional assignment of DEPLOY_DIR_IMAGE in bitbake.conf?

[Robert P. J. Day]

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On Tue, 22 Jul 2014, Christopher Larson wrote:

>
> On Tue, Jul 22, 2014 at 9:36 AM, Robert P. J. Day <rpjday@crashcourse.ca> wrote:
>         quite possibly another silly question, but i'm perusing poky's
>       version of bitbake.conf and i see this:
>
>       DEPLOY_DIR ?= "${TMPDIR}/deploy"
>       DEPLOY_DIR_TAR = "${DEPLOY_DIR}/tar"
>       DEPLOY_DIR_IPK = "${DEPLOY_DIR}/ipk"
>       DEPLOY_DIR_RPM = "${DEPLOY_DIR}/rpm"
>       DEPLOY_DIR_DEB = "${DEPLOY_DIR}/deb"
>       DEPLOY_DIR_IMAGE ?= "${DEPLOY_DIR}/images/${MACHINE}"
>       DEPLOY_DIR_TOOLS = "${DEPLOY_DIR}/tools"
>
>         now, what is the value of using "?=" to set DEPLOY_DIR_IMAGE, rather
>       than just "=". i know what "?=" represents, but i normally expect to
>       see it in a context where someone might have set it earlier to some
>       other value, but this is in bitbake.conf, before any of the "include"
>       or "require" directives to pull in any of the other .conf files. so in
>       the midst of all those other DEPLOY_DIR_* hard assignments, why is the
>       images directory a conditional install?
>
>
> s/install/define/

  um, quite so. :-P

> If there's a ?= done before any includes in bitbake.conf, either its
> position in the file has changed, or it's set that way to allow the
> user to add those variables to the env whitelist and set them in the
> environment, as the env is set before bitbake.conf is parsed.

  ah, gotcha. so the obvious question is, who decides which variables
merit this sort of behaviour and which don't? why two variables out of
the DEPLOY_DIR_* variables and not the rest? seems sort of arbitrary.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

Re: why conditional assignment of DEPLOY_DIR_IMAGE in bitbake.conf?

[Mark Hatle]

On 7/22/14, 11:53 AM, Robert P. J. Day wrote:
> On Tue, 22 Jul 2014, Christopher Larson wrote:
>
>>
>> On Tue, Jul 22, 2014 at 9:36 AM, Robert P. J. Day <rpjday@crashcourse.ca> wrote:
>>          quite possibly another silly question, but i'm perusing poky's
>>        version of bitbake.conf and i see this:
>>
>>        DEPLOY_DIR ?= "${TMPDIR}/deploy"
>>        DEPLOY_DIR_TAR = "${DEPLOY_DIR}/tar"
>>        DEPLOY_DIR_IPK = "${DEPLOY_DIR}/ipk"
>>        DEPLOY_DIR_RPM = "${DEPLOY_DIR}/rpm"
>>        DEPLOY_DIR_DEB = "${DEPLOY_DIR}/deb"
>>        DEPLOY_DIR_IMAGE ?= "${DEPLOY_DIR}/images/${MACHINE}"
>>        DEPLOY_DIR_TOOLS = "${DEPLOY_DIR}/tools"
>>
>>          now, what is the value of using "?=" to set DEPLOY_DIR_IMAGE, rather
>>        than just "=". i know what "?=" represents, but i normally expect to
>>        see it in a context where someone might have set it earlier to some
>>        other value, but this is in bitbake.conf, before any of the "include"
>>        or "require" directives to pull in any of the other .conf files. so in
>>        the midst of all those other DEPLOY_DIR_* hard assignments, why is the
>>        images directory a conditional install?
>>
>>
>> s/install/define/
>
>    um, quite so. :-P
>
>> If there's a ?= done before any includes in bitbake.conf, either its
>> position in the file has changed, or it's set that way to allow the
>> user to add those variables to the env whitelist and set them in the
>> environment, as the env is set before bitbake.conf is parsed.
>
>    ah, gotcha. so the obvious question is, who decides which variables
> merit this sort of behaviour and which don't? why two variables out of
> the DEPLOY_DIR_* variables and not the rest? seems sort of arbitrary.

Who, whoever sends patches with a need.

I know I've used both the DEPLOY_DIR and DEPLOY_DIR_IMAGE before to simplify a 
few things on the command line.. (but I don't use them regularly).

The others being based on those have not caused me problems the few times I've 
wanted to override it from the command line.

--Mark

> rday
>
>
>