Add kern.geom.part.separator tunable. This makes it possible

to specify an optional separator to insert before partition name;
eg if it's set to "c/", you'll get "ada0c/s1" instead of "ada0s1".
(It cannot be set to just “/“, since ada0 is a device node, not
a directory.)

Reviewed by:	imp
MFC after:	2 weeks
Sponsored by:	Klara Inc.
Differential Revision:	https://reviews.freebsd.org/D22193

lib/geom/part/gpart.8

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 3, 2019
+.Dd December 13, 2019
 .Dt GPART 8
 .Os
 .Sh NAME
@@ -1260,6 +1260,14 @@ If this variable is set to a non-zero value, the module will automatically
 recalculate the user-specified offset and size for alignment with the CHS
 geometry.
 Otherwise the values will be left unchanged.
+.It Va kern.geom.part.separator : No ""
+Specify an optional separator that will be inserted between the GEOM name
+and partition name.
+This variable is a
+.Xr loader 8
+tunable.
+Note that setting this variable may break software which assumes a particular
+naming scheme.
 .El
 .Sh EXIT STATUS
 Exit status is 0 on success, and 1 if the command fails.

sys/geom/part/g_part.c

@@ -147,6 +147,10 @@ static u_int allow_nesting = 0;
 SYSCTL_UINT(_kern_geom_part, OID_AUTO, allow_nesting,
     CTLFLAG_RWTUN, &allow_nesting, 0,
     "Allow additional levels of nesting");
+char g_part_separator[MAXPATHLEN] = "";
+SYSCTL_STRING(_kern_geom_part, OID_AUTO, separator,
+    CTLFLAG_RDTUN, &g_part_separator, sizeof(g_part_separator),
+    "Partition name separator");
 
 /*
  * The GEOM partitioning class.

sys/geom/part/g_part.h

@@ -228,6 +228,8 @@ void g_part_geometry_heads(off_t, u_int, off_t *, u_int *);
 
 int g_part_modevent(module_t, int, struct g_part_scheme *);
 
+extern char g_part_separator[];
+
 #define	G_PART_SCHEME_DECLARE(name)				\
     static int name##_modevent(module_t mod, int tp, void *d)	\
     {								\

sys/geom/part/g_part_if.m

@@ -48,7 +48,7 @@ CODE {
 	{
 		char buf[32];
 
-		sbuf_printf(sb, "%s%s", pfx,
+		sbuf_printf(sb, "%s%s%s", pfx, g_part_separator,
 		    G_PART_NAME(table, entry, buf, sizeof(buf)));
 	}