why would a recipe have both do_install() and do_install_append()?

["Robert P. J. Day" <rpjday@crashcourse.ca>]

  i'm probably just misreading something, but what is the point of a
recipe having both a do_install() and do_install_append() function?
for example, here's part of e2fsprogs_1.42.1.bb:

do_install () {
        oe_runmake 'DESTDIR=${D}' install
        oe_runmake 'DESTDIR=${D}' install-libs
        # We use blkid from util-linux now so remove from here
        rm -f ${D}${base_libdir}/libblkid*
        rm -rf ${D}${includedir}/blkid
        rm -f ${D}${base_libdir}/pkgconfig/blkid.pc
}

do_install_append () {
        # e2initrd_helper and the pkgconfig files belong in libdir
        if [ ! ${D}${libdir} -ef ${D}${base_libdir} ]; then
                install -d ${D}${libdir}
                mv ${D}${base_libdir}/e2initrd_helper ${D}${libdir}
                mv ${D}${base_libdir}/pkgconfig ${D}${libdir}
        fi
}

  how does that differ from simply defining a single do_install()
routine?  i'm willing for this to be a dumb question.

rday

-- 

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

Twitter:                                       http://twitter.com/rpjday
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