[FE training-materials-updates] Makefile: add a comment explaining why we're doing a filter on the slide list

[Thomas Petazzoni]

Repository : git://git.free-electrons.com/training-materials.git

On branch  : kernel-ng
Link       : http://git.free-electrons.com/training-materials/commit/?id=b772a0839c91a554fbcf437016fad89c44a339e4

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commit b772a0839c91a554fbcf437016fad89c44a339e4
Author: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
Date:   Tue Aug 27 17:16:13 2013 +0200

    Makefile: add a comment explaining why we're doing a filter on the slide list
    
    Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>


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b772a0839c91a554fbcf437016fad89c44a339e4
 Makefile |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Makefile b/Makefile
index 681562f..cae5bc0 100644
--- a/Makefile
+++ b/Makefile
@@ -319,6 +319,11 @@ SLIDES_CHAPTERS      = $($(call UPPERCASE, $(SLIDES_TRAINING))_SLIDES)
 SLIDES_COMMON_AFTER  = common/slide-footer.tex
 else
 SLIDES_TRAINING      = $(firstword $(subst -, ,  $(SLIDES)))
+# We might be building multiple chapters that share a common
+# prefix. In this case, we want to build them in the order they are
+# listed in the <training>_SLIDES variable that corresponds to the
+# current training, as identified by the first component of the
+# chapter name.
 SLIDES_CHAPTERS      = $(filter $(SLIDES)%, $($(call UPPERCASE, $(SLIDES_TRAINING))_SLIDES))
 ifeq ($(words $(SLIDES_CHAPTERS)),1)
 SLIDES_COMMON_BEFORE = common/slide-header.tex common/single-subsection-slide-title.tex