initial net-usershares feature

This is applicable at least to XFCE and MATE based images
(plugins for the appropriate file managers are available).

NB: basically untested with installers.

features.in/net-usershares/config.mk

@@ -0,0 +1,5 @@
+# requires thunar-shares-plugin or mate-user-share to make sense
+use/net-usershares: use/services use/deflogin
+	@$(call add,GROUPS,sambashare)
+	@$(call add,DEFAULT_SERVICES_ENABLE,smb nmb)
+	@$(call add,THE_PACKAGES,libshell)

features.in/net-usershares/rootfs/image-scripts.d/85-samba-usershares.sh

@@ -0,0 +1,36 @@
+#!/bin/sh -efu
+
+[ -s /etc/samba/smb.conf ] || exit 0
+
+. shell-config
+
+USERSHARES_DIR="/var/lib/samba/usershares"
+USERSHARES_GROUP="sambashare"
+DEFAULT_GROUPS='cdwriter cdrom audio proc radio camera floppy xgrp scanner uucp' ###
+GROUPS_FILE="/usr/share/install3/default-groups"
+
+mkdir -p "$USERSHARES_DIR"
+groupadd -r "$USERSHARES_GROUP"
+chown root:"$USERSHARES_GROUP" "$USERSHARES_DIR"
+chmod 1770 "$USERSHARES_DIR"
+
+USERSHARES_OPTIONS="# ----------------------- User Shares Options -------------------------\n\tusershare path = $USERSHARES_DIR\n\tusershare max shares = 100\n\tusershare allow guests = yes\n\tusershare owner only = yes"
+
+sed -i -e "\|^\[global\]|a$USERSHARES_OPTIONS" \
+        -e "s/workgroup = MYGROUP/workgroup = WORKGROUP/" \
+        "/etc/samba/smb.conf"
+
+# Create group file for alterator-users
+if [ ! -s "$GROUPS_FILE" ]; then
+        mkdir -p "${GROUPS_FILE%/*}"
+        echo "$DEFAULT_GROUPS" >"$GROUPS_FILE"
+fi
+
+# Add USERSHARES_GROUP to the default groups list.
+echo "$USERSHARES_GROUP" >>"$GROUPS_FILE"
+
+# Permissions for home dir must be 0701
+tab="$(printf "\t")"
+shell_config_set "/etc/login.defs" UMASK 076 "$tab" "$tab"
+
+# smb and nmb services must be enabled