Index: sys/fs/devfs/devfs_vnops.c
===================================================================
--- sys/fs/devfs/devfs_vnops.c
+++ sys/fs/devfs/devfs_vnops.c
@@ -769,16 +769,17 @@
 
 /* ARGSUSED */
 static int
-devfs_ioctl_f(struct file *fp, u_long com, void *data, struct ucred *cred, struct thread *td)
+devfs_ioctl_f(struct file *fp, u_long com, void *data, struct ucred *cred,
+    struct thread *td)
 {
 	struct cdev *dev;
 	struct cdevsw *dsw;
 	struct vnode *vp;
 	struct vnode *vpold;
-	int error, i, ref;
-	const char *p;
+	char *p;
 	struct fiodgname_arg *fgn;
 	struct file *fpop;
+	int error, i, ref;
 
 	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw, &ref);
@@ -794,12 +795,16 @@
 		return (0);
 	} else if (com == FIODGNAME) {
 		fgn = data;
-		p = devtoname(dev);
-		i = strlen(p) + 1;
-		if (i > fgn->len)
-			error = EINVAL;
-		else
-			error = copyout(p, fgn->buf, i);
+		p = malloc(SPECNAMELEN + 1, M_TEMP, M_WAITOK);
+		error = dsw->d_devname(dev, p, SPECNAMELEN + 1);
+		if (error == 0) {
+			i = strlen(p) + 1;
+			if (i > fgn->len)
+				error = EINVAL;
+			else
+				error = copyout(p, fgn->buf, i);
+		}
+		free(p, M_TEMP);
 		td->td_fpop = fpop;
 		dev_relthread(dev, ref);
 		return (error);
Index: sys/kern/kern_conf.c
===================================================================
--- sys/kern/kern_conf.c
+++ sys/kern/kern_conf.c
@@ -301,6 +301,14 @@
 	biofinish(bp, NULL, ENXIO);
 }
 
+static int
+dead_devname(struct cdev *dev, char *buf, size_t len)
+{
+
+	strlcpy(buf, dev->si_name, len);
+	return (0);
+}
+
 #define dead_dump	(dumper_t *)enxio
 #define dead_kqfilter	(d_kqfilter_t *)enxio
 #define dead_mmap_single (d_mmap_single_t *)enodev
@@ -318,7 +326,8 @@
 	.d_name =	"dead",
 	.d_dump =	dead_dump,
 	.d_kqfilter =	dead_kqfilter,
-	.d_mmap_single = dead_mmap_single
+	.d_mmap_single = dead_mmap_single,
+	.d_devname =	dead_devname,
 };
 
 /* Default methods if driver does not specify method */
@@ -531,6 +540,22 @@
 	return (retval);
 }
 
+static int
+giant_devname(struct cdev *dev, char *buf, size_t len)
+{
+	struct cdevsw *dsw;
+	int ref, retval;
+
+	dsw = dev_refthread(dev, &ref);
+	if (dsw == NULL)
+		return (ENXIO);
+	mtx_lock(&Giant);
+	retval = dsw->d_gianttrick->d_devname(dev, buf, len);
+	mtx_unlock(&Giant);
+	dev_relthread(dev, ref);
+	return (retval);
+}
+
 static void
 notify(struct cdev *dev, const char *ev, int flags)
 {
@@ -623,7 +648,7 @@
 		return (0);
 	}
 
-	if (devsw->d_version != D_VERSION_03) {
+	if (devsw->d_version != D_VERSION_04) {
 		printf(
 		    "WARNING: Device driver \"%s\" has wrong version %s\n",
 		    devsw->d_name == NULL ? "???" : devsw->d_name,
@@ -639,6 +664,7 @@
 		devsw->d_strategy = dead_strategy;
 		devsw->d_dump = dead_dump;
 		devsw->d_kqfilter = dead_kqfilter;
+		devsw->d_devname = dead_devname;
 	}
 	
 	if (devsw->d_flags & D_NEEDGIANT) {
@@ -669,13 +695,13 @@
 	FIXUP(d_strategy,	no_strategy,	giant_strategy);
 	FIXUP(d_kqfilter,	no_kqfilter,	giant_kqfilter);
 	FIXUP(d_mmap_single,	no_mmap_single,	giant_mmap_single);
+	FIXUP(d_devname,	dead_devname,	giant_devname);
+#undef FIXUP
 
-	if (devsw->d_dump == NULL)	devsw->d_dump = no_dump;
-
+	if (devsw->d_dump == NULL)
+		devsw->d_dump = no_dump;
 	LIST_INIT(&devsw->d_devs);
-
 	devsw->d_flags |= D_INIT;
-
 	if (dsw2 != NULL)
 		cdevsw_free_devlocked(dsw2);
 	return (0);
Index: sys/sys/conf.h
===================================================================
--- sys/sys/conf.h
+++ sys/sys/conf.h
@@ -106,22 +106,25 @@
 struct vm_object;
 struct vnode;
 
-typedef int d_open_t(struct cdev *dev, int oflags, int devtype, struct thread *td);
-typedef int d_fdopen_t(struct cdev *dev, int oflags, struct thread *td, struct file *fp);
-typedef int d_close_t(struct cdev *dev, int fflag, int devtype, struct thread *td);
-typedef void d_strategy_t(struct bio *bp);
+typedef int d_open_t(struct cdev *dev, int oflags, int devtype,
+	    struct thread *td);
+typedef int d_fdopen_t(struct cdev *dev, int oflags, struct thread *td,
+	    struct file *fp);
+typedef int d_close_t(struct cdev *dev, int fflag, int devtype,
+	    struct thread *td);
+typedef int d_devname_t(struct cdev *dev, char *buf, size_t len);
 typedef int d_ioctl_t(struct cdev *dev, u_long cmd, caddr_t data,
-		      int fflag, struct thread *td);
-
+	    int fflag, struct thread *td);
 typedef int d_read_t(struct cdev *dev, struct uio *uio, int ioflag);
 typedef int d_write_t(struct cdev *dev, struct uio *uio, int ioflag);
 typedef int d_poll_t(struct cdev *dev, int events, struct thread *td);
 typedef int d_kqfilter_t(struct cdev *dev, struct knote *kn);
 typedef int d_mmap_t(struct cdev *dev, vm_ooffset_t offset, vm_paddr_t *paddr,
-		     int nprot, vm_memattr_t *memattr);
+	    int nprot, vm_memattr_t *memattr);
 typedef int d_mmap_single_t(struct cdev *cdev, vm_ooffset_t *offset,
-    vm_size_t size, struct vm_object **object, int nprot);
+	    vm_size_t size, struct vm_object **object, int nprot);
 typedef void d_purge_t(struct cdev *dev);
+typedef void d_strategy_t(struct bio *bp);
 
 typedef int dumper_t(
 	void *_priv,		/* Private to the driver. */
@@ -159,7 +162,8 @@
 #define	D_VERSION_01	0x17032005	/* Add d_uid,gid,mode & kind */
 #define	D_VERSION_02	0x28042009	/* Add d_mmap_single */
 #define	D_VERSION_03	0x17122009	/* d_mmap takes memattr,vm_ooffset_t */
-#define	D_VERSION	D_VERSION_03
+#define	D_VERSION_04	0x55e81e6f	/* d_devname */
+#define	D_VERSION	D_VERSION_04
 
 /*
  * Flags used for internal housekeeping
@@ -186,6 +190,7 @@
 	d_kqfilter_t		*d_kqfilter;
 	d_purge_t		*d_purge;
 	d_mmap_single_t		*d_mmap_single;
+	d_devname_t		*d_devname;
 
 	int32_t			d_spare0[3];
 	void			*d_spare1[3];