[PATCH v2 for-7.0] scripts: Explain the difference between linux-headers and standard-headers

[Peter Maydell]

If you don't know it, it's hard to figure out the difference between
the linux-headers folder and the include/standard-headers folder.
So let's add a short explanation to clarify the difference.

Suggested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
v1 of this was from Thomas; I suggested some expanded wording
and since that made the patch pretty much entirely my text
Thomas suggested I send this under my name.
---
 scripts/update-linux-headers.sh | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/scripts/update-linux-headers.sh b/scripts/update-linux-headers.sh
index fea4d6eb655..d23851e1d3b 100755
--- a/scripts/update-linux-headers.sh
+++ b/scripts/update-linux-headers.sh
@@ -9,6 +9,22 @@
 #
 # This work is licensed under the terms of the GNU GPL version 2.
 # See the COPYING file in the top-level directory.
+#
+# The script will copy the headers into two target folders:
+#
+# - linux-headers/ for files that are required for compiling on a
+#   Linux host.  Generally we have these so we can use kernel structs
+#   and defines that are more recent than the headers that might be
+#   in /usr/include/linux on the host system.  Usually this script
+#   can do simple file copies for these headers.
+#
+# - include/standard-headers/ for files that are used for guest
+#   device emulation and are required on all hosts.  For instance, we
+#   get our definitions of the virtio structures from the Linux
+#   kernel headers, but we need those definitions regardless of which
+#   host OS we are building on.  This script has to be careful to
+#   sanitize the headers to remove any use of Linux-specifics such as
+#   types like "__u64".  This work is done in the cp_portable function.
 
 tmpdir=$(mktemp -d)
 linux="$1"
-- 
2.25.1