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From "Bailey, Darragh" <dbai...@hp.com>
Subject Better alternative than using foreach, for and if/then/else?
Date Wed, 05 May 2010 13:24:25 GMT

Have recently just started using Ant, with the goal to using it as the default build tool
across an entire project. While most of the project will be java based, there are a few parts
that won't be and I'm trying to make ant work as effectively as possible for these sections.

One of them just happens to be a kernel module. While there will be a makefile called by the
Ant target in the end, I'm trying to set Ant up as the entry point so that developers moving
between different parts of the project will get the same interface and the same targets to
be called. It also simplifies the work around a continuous build tool, in that it doesn't
have to run differently for the different components.


For the kernel module build, I'm trying to allow for more than 1 kernel version and different
kernel variants. In most cases the kernel version will be 2.6.18-194.el5 (RHEL5 Update 5 kernel)
and the variant will be the default. However at times developers will want to build against
multiple kernel versions and/or variants when developing/debugging issues.

Examples:
Default Properties
kernel.versions = 2.6.18-194.el5
kernel.variants = ""

Additionally "kernel.${kernel.version}.variants = xxx" can be used to specify the variants
for a particular version, rather than using the default set. I use "" to represent the default
variant simply because that is the method that works best when building kmod-* rpm packages
as I'm using a spec template similar to what fedora uses.

Properties set by a Developer
kernel.versions = 2.6.18-194.el5 2.6.33-k.org
kernel.variants = ""
kernel.2.6.18-194.el5.variants = xen



Coming from a make background I was previously used to expanding targets dynamically based
on values set in properties in the makefile in order to reference multiple kernel versions
and variants and then using pattern based rules to build the necessary target. Right now I've
got something partially working in Ant using the foreach/for tasks from ant-contrib, but I'm
not sure that this is the best way to accomplish this. I'm also using if/the/else to work
around the use of "" which Ant doesn't really like when it comes to specifying an empty value
for a property.

I know I have a bug in the xml below, in that the for loop I attempt to change properties
which by default Ant won't overwrite after setting them initially. Like I mentioned before
I'm very much used to make and I've yet to fully get to grips with Ant.


Any suggestions on other Ant tasks that could simplify this would be very welcome:


  <target name="compile" if="isLinux"
          description="Compile the source against all requested kernel versions and variants">
    <!-- determine the default kernel version, only set if not already set -->
    <exec executable="uname" outputproperty="kernel.versions">
      <arg value="-r" />
    </exec>
    <foreach target="compile-module" list="${kernel.versions}" delimiter=" " param="kernel.version"
/>
  </target>


  <!-- default compile task, restrict to running on linux also try to avoid rebuilding
if
      it has already been compiled and the sources have not be modified.

      TODO:
        Handle if different kernel version or variants used
        Handle building for multiple variants
        Handle building for multiple kernel versions

        Compile the source against the specified kernel version and variant
  -->
  <target name="compile-module" depends="init" if="isLinux" >


    <!-- Will set the variants to the default value only if not already set (i.e. doesn't
override) -->
    <property name="kernel.${kernel.version}.variants" value="${kernel.variants}" />
    <propertycopy property="kernel.currver.variants" override="true" from="kernel.${kernel.version}.variants"
/>

    <for list="${kernel.currver.variants}" param="kernel.variant" delimiter=" " trim="true">
      <sequential>
        <if>
          <equals arg1="@{kernel.variant}" arg2='""' />
          <then>
            <property name="dir.kernel.build" location="/lib/modules/${kernel.version}/build"
/>
            <property name="dir.module.build" location="${dir.build}/output/${kernel.version}"
/>
          </then>
          <else>
            <property name="dir.kernel.build" location="/lib/modules/${kernel.version}@{kernel.variant}/build"
/>
            <property name="dir.module.build" location="${dir.build}/output/${kernel.version}@{kernel.variant}"
/>
          </else>
        </if>
        <!--<property name="kernel.arch" />-->
        <echoproperties prefix="name."/>
        <echoproperties prefix="dir."/>
        <echoproperties prefix="kernel."/>
        <echo message="kernel.variant='@{kernel.variant}'" />
        <!-- Copy the src to a directory under the build directory, excluding hidden files
-->
        <copy todir="${dir.module.build}">
          <fileset dir="${dir.src}">
            <exclude name="**/.*" />
          </fileset>
        </copy>

        <!-- execute the require make command, specifying the kernel directory to use -->
        <exec executable="make">
          <arg value="-C" />
          <arg value="${dir.kernel.build}" />
          <arg value="M=${dir.module.build}" />
          <arg value="modules" />
        </exec>
      </sequential>
    </for>
  </target>



--
Regards,
Darragh Bailey

Systems Software Engineer
Hewlett Packard Galway Ltd.

Postal Address:    Hewlett Packard Galway Limited, Ballybrit Business Park, Galway
Registered Office: Hewlett Packard Galway Limited, 63-74 Sir John Rogerson's Quay Dublin 2
Registered Number: 361933 

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