https://bugs.gentoo.org/444918

Taken from
http://svnweb.freebsd.org/base/stable/9/sys/kern/vfs_subr.c?r1=237839&r2=239755&view=patch

FYI,
http://svnweb.freebsd.org/base?view=revision&revision=239588

--- stable/9/sys/kern/vfs_subr.c	2012/06/30 14:17:59	237839
+++ stable/9/sys/kern/vfs_subr.c	2012/08/27 20:25:26	239755
@@ -41,6 +41,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_compat.h"
 #include "opt_ddb.h"
 #include "opt_watchdog.h"
 
@@ -3110,22 +3111,50 @@
 /*
  * Fill in a struct xvfsconf based on a struct vfsconf.
  */
-static void
-vfsconf2x(struct vfsconf *vfsp, struct xvfsconf *xvfsp)
+static int
+vfsconf2x(struct sysctl_req *req, struct vfsconf *vfsp)
 {
+	struct xvfsconf xvfsp;
 
-	strcpy(xvfsp->vfc_name, vfsp->vfc_name);
-	xvfsp->vfc_typenum = vfsp->vfc_typenum;
-	xvfsp->vfc_refcount = vfsp->vfc_refcount;
-	xvfsp->vfc_flags = vfsp->vfc_flags;
+	bzero(&xvfsp, sizeof(xvfsp));
+	strcpy(xvfsp.vfc_name, vfsp->vfc_name);
+	xvfsp.vfc_typenum = vfsp->vfc_typenum;
+	xvfsp.vfc_refcount = vfsp->vfc_refcount;
+	xvfsp.vfc_flags = vfsp->vfc_flags;
 	/*
 	 * These are unused in userland, we keep them
 	 * to not break binary compatibility.
 	 */
-	xvfsp->vfc_vfsops = NULL;
-	xvfsp->vfc_next = NULL;
+	xvfsp.vfc_vfsops = NULL;
+	xvfsp.vfc_next = NULL;
+	return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
 }
 
+#ifdef COMPAT_FREEBSD32
+struct xvfsconf32 {
+	uint32_t	vfc_vfsops;
+	char		vfc_name[MFSNAMELEN];
+	int32_t		vfc_typenum;
+	int32_t		vfc_refcount;
+	int32_t		vfc_flags;
+	uint32_t	vfc_next;
+};
+
+static int
+vfsconf2x32(struct sysctl_req *req, struct vfsconf *vfsp)
+{
+	struct xvfsconf32 xvfsp;
+
+	strcpy(xvfsp.vfc_name, vfsp->vfc_name);
+	xvfsp.vfc_typenum = vfsp->vfc_typenum;
+	xvfsp.vfc_refcount = vfsp->vfc_refcount;
+	xvfsp.vfc_flags = vfsp->vfc_flags;
+	xvfsp.vfc_vfsops = 0;
+	xvfsp.vfc_next = 0;
+	return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
+}
+#endif
+
 /*
  * Top level filesystem related information gathering.
  */
@@ -3133,14 +3162,16 @@
 sysctl_vfs_conflist(SYSCTL_HANDLER_ARGS)
 {
 	struct vfsconf *vfsp;
-	struct xvfsconf xvfsp;
 	int error;
 
 	error = 0;
 	TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
-		bzero(&xvfsp, sizeof(xvfsp));
-		vfsconf2x(vfsp, &xvfsp);
-		error = SYSCTL_OUT(req, &xvfsp, sizeof xvfsp);
+#ifdef COMPAT_FREEBSD32
+		if (req->flags & SCTL_MASK32)
+			error = vfsconf2x32(req, vfsp);
+		else
+#endif
+			error = vfsconf2x(req, vfsp);
 		if (error)
 			break;
 	}
@@ -3160,7 +3191,6 @@
 	int *name = (int *)arg1 - 1;	/* XXX */
 	u_int namelen = arg2 + 1;	/* XXX */
 	struct vfsconf *vfsp;
-	struct xvfsconf xvfsp;
 
 	printf("WARNING: userland calling deprecated sysctl, "
 	    "please rebuild world\n");
@@ -3184,9 +3214,12 @@
 				break;
 		if (vfsp == NULL)
 			return (EOPNOTSUPP);
-		bzero(&xvfsp, sizeof(xvfsp));
-		vfsconf2x(vfsp, &xvfsp);
-		return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
+#ifdef COMPAT_FREEBSD32
+		if (req->flags & SCTL_MASK32)
+			return (vfsconf2x32(req, vfsp));
+		else
+#endif
+			return (vfsconf2x(req, vfsp));
 	}
 	return (EOPNOTSUPP);
 }