* NEWS, lib/getdef.c, man/login.defs.5.xml: New login.defs

variable: MAX_MEMBERS_PER_GROUP. Used for the split groups support.
* lib/commonio.c, lib/commonio.h: Add an open_hook and close_hook
  operation. They are called after the database is actually opened
  and parse, or before it is closed.
* lib/groupio.c: Add an open_hook to merge split groups, and an
  close group to split groups if MAX_MEMBERS_PER_GROUP is set.
  This fixes gpasswd and chgpasswd when split groups are used.
* lib/sgroupio.c, lib/shadowio.c, lib/pwio.c: No open or close
  hooks for these databases. (unsure about what should be the gshadow
  behavior for split groups)

man/login.defs.5.xml

@@ -121,6 +121,36 @@
 	  </para>
 	</listitem>
       </varlistentry>
+      <varlistentry>
+	<term>MAX_MEMBERS_PER_GROUP (number)</term>
+	<listitem>
+	  <para>
+	    Maximum members per group entry. When the maximum is reached,
+	    a new group entry (line) is started is
+	    <filename>/etc/group</filename> (with the same name, same
+	    password, and same GID).
+	  </para>
+	  <para>
+	    The default value is 0, meaning that there are no limits in
+	    the number of members in a group.
+	  </para>
+	  <!-- Note: on HP, split groups have the same ID, but different
+	             names. -->
+	  <para>
+	    This feature (split group) permits to limit the length of
+	    lines in the group file. This is useful to make sure that
+	    lines for NIS groups are not larger than 1024 characters.
+	  </para>
+	  <para>
+	    If you need to enforce such limit, you can use 25.
+	  </para>
+	  <para>
+	    Note: split groups may not be supported by all tools (even in
+	    the Shadow toolsuite. Yous hould not use this variable unless
+	    you really need it.
+	  </para>
+	</listitem>
+      </varlistentry>
       <varlistentry>
 	<term>MD5_CRYPT_ENAB (boolean)</term>
 	<listitem>