[yocto] FILESEXTRAPATHS needs to be explained *way* better

[Robert P. J. Day]

  first time digging into FILESPATH and .bbappend files, and i tested
the effect of setting something trivial to see what would happen:

FILESEXTRAPATHS_prepend := "rday"

did this for "netbase" in meta-ti layer, and checked the resulting
value of FILESPATH and (nicely formatted so you can read it), i got:

FILESPATH="rday/linux-gnueabi
rday/arm
rday/build-linux
rday/pn-netbase
rday/beagleboard
rday/omap3
rday/armv7a
rday/
rday/class-target
rday/forcevariable
rday/libc-glibc
rday/
/home/rpjday/OE/dist/layers/oe-core/meta/recipes-core/netbase/netbase-5.0/linux-gnueabi
/home/rpjday/OE/dist/layers/oe-core/meta/recipes-core/netbase/netbase-5.0/arm
/home/rpjday/OE/dist/layers/oe-core/meta/recipes-core/netbase/netbase-5.0/build-linux
/home/rpjday/OE/dist/layers/oe-core/meta/recipes-core/netbase/netbase-5.0/pn-netbase
... snip ...

  that is totally *not* what i expected given the explanation of that
variable in the current docs (unless i've missed it).  obviously,
FILESEXTRAPATHS doesn't just add individual directories to FILESPATH
-- it processes and adds based on OVERRIDES, which is fine but that's
not at all obvious.

  in addition, there is absolutely no need to add a ":" to the value
as the processing adds that for you, so the many, many examples of

FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

is potentially confusing to folks reading the code.  (that trailing
":" doesn't hurt, but it has no value.)

  at what point is this variable explained in detail?

rday

-- 

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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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