dev-manual: reverse "=" and "+=" for IMAGE_FEATURES

Pretty sure these assignments are in the reverse order.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>

---

You probably want += in both cases. Also, adding to IMAGE_FEATURES is 
more appropriately done in an image recipe, while adding to 
EXTRA_IMAGE_FEATURES is typically done in the local.conf, so:

            <para>
                To create the read-only root filesystem, simply add the
                "read-only-rootfs" feature to your image.
                Either add the following statement to your image recipe:
                <literallayout class='monospaced'>
     IMAGE_FEATURES += "read-only-rootfs"
                </literallayout>
                or add the following statement to the
                <filename>local.conf</filename> file found in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
                </literallayout>
            </para>

//Peter

> -----Original Message-----
> From: docs@lists.yoctoproject.org <docs@lists.yoctoproject.org> On Behalf
> Of rpjday@crashcourse.ca
> Sent: den 6 april 2020 22:33
> To: YP docs mailing list <docs@lists.yoctoproject.org>
> Subject: [docs] [PATCH] dev-manual: reverse "=" and "+=" for
> IMAGE_FEATURES
> 
> Pretty sure these assignments are in the reverse order.
> 
> Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
> 
> ---
> 
> diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml
> b/documentation/dev-manual/dev-manual-common-tasks.xml
> index 2b8868b62..b9d527486 100644
> --- a/documentation/dev-manual/dev-manual-common-tasks.xml
> +++ b/documentation/dev-manual/dev-manual-common-tasks.xml
> @@ -11202,11 +11202,11 @@
>                  <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build
> Directory</ulink>
>                  causes the build system to create a read-only root
> filesystem:
>                  <literallayout class='monospaced'>
> -     IMAGE_FEATURES = "read-only-rootfs"
> +     IMAGE_FEATURES += "read-only-rootfs"
>                  </literallayout>
>                  or
>                  <literallayout class='monospaced'>
> -     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
> +     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
>                  </literallayout>
>              </para>
> 
> 
> --
> 
> ========================================================================
> Robert P. J. Day                                 Ottawa, Ontario, CANADA
>                          http://crashcourse.ca
> 
> Twitter:                                       http://twitter.com/rpjday
> LinkedIn:                               http://ca.linkedin.com/in/rpjday
> ========================================================================
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On Tue, 7 Apr 2020, Peter Kjellerstedt wrote:

> You probably want += in both cases. Also, adding to IMAGE_FEATURES is
> more appropriately done in an image recipe, while adding to
> EXTRA_IMAGE_FEATURES is typically done in the local.conf, so:
>
>             <para>
>                 To create the read-only root filesystem, simply add the
>                 "read-only-rootfs" feature to your image.
>                 Either add the following statement to your image recipe:
>                 <literallayout class='monospaced'>
>      IMAGE_FEATURES += "read-only-rootfs"
>                 </literallayout>
>                 or add the following statement to the
>                 <filename>local.conf</filename> file found in the
>                 <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>:
>                 <literallayout class='monospaced'>
>      EXTRA_IMAGE_FEATURES += "read-only-rootfs"
>                 </literallayout>
>             </para>
>
> //Peter

  i would disagree with your second position just from a stylistic
point of view, as there are variables in OE where the base form (VAR)
is normally set in a recipe file, while there is the additional form
EXTRA_VAR that is specifically meant to be just *set* in your
local.conf, knowing that the underlying logic will do the right thing
with it and you don't need to worry about "+=" versus "_append", which
is exactly what EXTRA_IMAGE_FEATURES is for.

  yes, using += with EXTRA_IMAGE_FEATURES will work just fine, but it
sort of defeats the purpose of having invented it in the first place.
i would, however, incorporate your additional explanation to make all
of this more obvious. v2 coming shortly ...

> > -----Original Message-----
> > From: docs@lists.yoctoproject.org <docs@lists.yoctoproject.org> On Behalf
> > Of rpjday@crashcourse.ca
> > Sent: den 6 april 2020 22:33
> > To: YP docs mailing list <docs@lists.yoctoproject.org>
> > Subject: [docs] [PATCH] dev-manual: reverse "=" and "+=" for
> > IMAGE_FEATURES
> >
> > Pretty sure these assignments are in the reverse order.
> >
> > Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
> >
> > ---
> >
> > diff --git a/documentation/dev-manual/dev-manual-common-tasks.xml
> > b/documentation/dev-manual/dev-manual-common-tasks.xml
> > index 2b8868b62..b9d527486 100644
> > --- a/documentation/dev-manual/dev-manual-common-tasks.xml
> > +++ b/documentation/dev-manual/dev-manual-common-tasks.xml
> > @@ -11202,11 +11202,11 @@
> >                  <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build
> > Directory</ulink>
> >                  causes the build system to create a read-only root
> > filesystem:
> >                  <literallayout class='monospaced'>
> > -     IMAGE_FEATURES = "read-only-rootfs"
> > +     IMAGE_FEATURES += "read-only-rootfs"
> >                  </literallayout>
> >                  or
> >                  <literallayout class='monospaced'>
> > -     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
> > +     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
> >                  </literallayout>
> >              </para>
> >
> >
> > --
> >
> > ========================================================================
> > Robert P. J. Day                                 Ottawa, Ontario, CANADA
> >                          http://crashcourse.ca
> >
> > Twitter:                                       http://twitter.com/rpjday
> > LinkedIn:                               http://ca.linkedin.com/in/rpjday
> > ========================================================================
>