Add FIOBMAP2 ioctl

This ioctl exposes VOP_BMAP information to userland. It can be used by
programs like fragmentation analyzers and optimized cp implementations. But
I'm using it to test fusefs's VOP_BMAP implementation. The "2" in the name
distinguishes it from the similar but incompatible FIBMAP ioctls in NetBSD
and Linux.  FIOBMAP2 differs from FIBMAP in that it uses a 64-bit block
number instead of 32-bit, and it also returns runp and runb.

Reviewed by:	mckusick
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D20705

sys/kern/vfs_vnops.c

@@ -1458,6 +1458,25 @@ vn_stat(struct vnode *vp, struct stat *sb, struct ucred *active_cred,
 	return (0);
 }
 
+/* generic FIOBMAP2 implementation */
+static int
+vn_ioc_bmap2(struct file *fp, struct fiobmap2_arg *arg, struct ucred *cred)
+{
+	struct vnode *vp = fp->f_vnode;
+	daddr_t lbn = arg->bn;
+	int error;
+
+	vn_lock(vp, LK_SHARED | LK_RETRY);
+#ifdef MAC
+	error = mac_vnode_check_read(cred, fp->f_cred, vp);
+	if (error == 0)
+#endif
+		error = VOP_BMAP(vp, lbn, NULL, &arg->bn, &arg->runp,
+			&arg->runb);
+	VOP_UNLOCK(vp, 0);
+	return (error);
+}
+
 /*
  * File table vnode ioctl routine.
  */
@@ -1481,6 +1500,9 @@ vn_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred,
 			if (error == 0)
 				*(int *)data = vattr.va_size - fp->f_offset;
 			return (error);
+		case FIOBMAP2:
+			return (vn_ioc_bmap2(fp, (struct fiobmap2_arg*)data,
+				active_cred));
 		case FIONBIO:
 		case FIOASYNC:
 			return (0);

sys/sys/filio.h

@@ -62,6 +62,13 @@ struct fiodgname_arg {
 /* Handle lseek SEEK_DATA and SEEK_HOLE for holey file knowledge. */
 #define	FIOSEEKDATA	_IOWR('f', 97, off_t)	/* SEEK_DATA */
 #define	FIOSEEKHOLE	_IOWR('f', 98, off_t)	/* SEEK_HOLE */
+struct fiobmap2_arg {
+	int64_t	bn;
+	int	runp;
+	int	runb;
+};
+/* Get the file's bmap info for the logical block bn */
+#define FIOBMAP2	_IOWR('f', 99, struct fiobmap2_arg)
 
 #ifdef _KERNEL
 #ifdef COMPAT_FREEBSD32

sys/ufs/ufs/ufs_bmap.c

@@ -200,12 +200,15 @@ ufs_bmaparray(vp, bn, bnp, nbp, runp, runb)
 			*bnp = blkptrtodb(ump, ip->i_din2->di_extb[-1 - bn]);
 			if (*bnp == 0)
 				*bnp = -1;
-			if (nbp == NULL)
-				panic("ufs_bmaparray: mapping ext data");
+			if (nbp == NULL) {
+				/* indirect block not found */
+				return (EINVAL);
+			}
 			nbp->b_xflags |= BX_ALTDATA;
 			return (0);
 		} else {
-			panic("ufs_bmaparray: blkno out of range");
+			/* blkno out of range */
+			return (EINVAL);
 		}
 		/*
 		 * Since this is FFS independent code, we are out of