When a drive can't be unmounted and returns EBUSY, gvfs calls "lsof -t /mountpoint" to find which processes have files open. This list is sent over the "show-processes" signal, which allows file managers to show which apps are preventing the unmount.
For this to work, sysutils/lsof needs to be around. The port should depend on it at runtime, ie. something along these lines:
diff --git a/devel/gvfs/Makefile b/devel/gvfs/Makefile
index 830823c13ecc..aad75271e9c1 100644
@@ -23,7 +23,8 @@ LIB_DEPENDS= libgcrypt.so:security/libgcrypt \
+RUN_DEPENDS= bsdisks>0:sysutils/bsdisks \
USES= gettext gnome libarchive localbase meson \
^Triage: give this a correct Summary and assign.