man/os-release: add a note about repeating entries

We didn't actually say that keys should not be repeated. At least the
examples in docs (both python and shell) would do that, and any simple
parser that builds a dictionary would most likely behave the same way.
But let's document this expectation, but also say how to deal with malformed
files.

diff --git a/man/os-release.xml b/man/os-release.xml
index 4acd1a9a575722351b05609cac67471bd0df5db0..7e3e9a73a8cb70900ed0ff2c1b3a6c7896629b56 100644 (file)
--- a/man/os-release.xml
+++ b/man/os-release.xml
@@ -75,6 +75,10 @@
     from earliest boot on, and hence must be located on the root file
     system.</para>
 
+    <para><filename>os-release</filename> must not contain repeating keys. Nevertheless, readers should pick
+    the entries later in the file in case of repeats, similarly to how a shell sourcing the file would. A
+    reader may warn about repeating entries.</para>
+
     <para>For a longer rationale for <filename>os-release</filename>
     please refer to the <ulink
     url="http://0pointer.de/blog/projects/os-release">Announcement of <filename>/etc/os-release</filename></ulink>.</para>