Add some documentation for /etc/portage/modules and metadata_overlay.
svn path=/main/trunk/; revision=3342
diff --git a/man/portage.5 b/man/portage.5
index 51e6f32..f124a10 100644
--- a/man/portage.5
+++ b/man/portage.5
@@ -37,6 +37,7 @@
.BR /etc/portage/
.nf
bashrc
+modules
package.mask
package.unmask
package.keywords
@@ -300,6 +301,28 @@
If needed, this file can be used to set up a special environment for ebuilds,
different from the standard root environment. The syntax is the same as for
any other bash script.
+
+.TP
+.BR modules
+This file can be used to override the metadata cache implementation. In
+practice, portdbapi.auxdbmodule is the only variable that the user will want to
+override.
+
+.I Example:
+.nf
+portdbapi.auxdbmodule = cache.metadata_overlay.database
+.fi
+
+The metadata_overlay cache module makes it possible to disable
+FEATURES="metadata-transfer" in \fBmake.conf\fR(5). When the user initially
+enables metadata_overlay in /etc/portage/modules, all of the cache files
+contained in /var/cache/edb/dep/${PORTDIR} must be manually removed in order
+to avoid unecessary cache regeneration. In addition, users of the
+metadata_overlay module must never modify eclasses in ${PORTDIR} because
+portage will not be able to detect that cache regeneration is necessary. If
+the user would like to modify eclasses, it is safe to use metadata_overlay
+together with PORTDIR_OVERLAY in \fBmake.conf\fR.
+
.TP
.BR package.mask
A list of DEPEND atoms to mask. Useful if specific versions of packages do
