Character device tape drivers are non-lseekable.

You can seek the tape, but you do it with the magic tape
control ioctl's, not with lseek/pread/pwrite.

drivers/ide/ide-tape.c

@@ -3755,10 +3755,6 @@ static ssize_t idetape_chrdev_read (struct file *file, char __user *buf,
 	idetape_tape_t *tape = drive->driver_data;
 	ssize_t bytes_read,temp, actually_read = 0, rc;
 
-	if (ppos != &file->f_pos) {
-		/* "A request was outside the capabilities of the device." */
-		return -ENXIO;
-	}
 #if IDETAPE_DEBUG_LOG
 	if (tape->debug_level >= 3)
 		printk(KERN_INFO "ide-tape: Reached idetape_chrdev_read, count %Zd\n", count);
@@ -3818,11 +3814,6 @@ static ssize_t idetape_chrdev_write (struct file *file, const char __user *buf,
 	idetape_tape_t *tape = drive->driver_data;
 	ssize_t retval, actually_written = 0;
 
-	if (ppos != &file->f_pos) {
-		/* "A request was outside the capabilities of the device." */
-		return -ENXIO;
-	}
-
 	/* The drive is write protected. */
 	if (tape->write_prot)
 		return -EACCES;
@@ -4187,6 +4178,7 @@ static int idetape_chrdev_open (struct inode *inode, struct file *filp)
 	idetape_pc_t pc;
 	int retval;
 
+	nonseekable_open(inode, filp);
 #if IDETAPE_DEBUG_LOG
 	printk(KERN_INFO "ide-tape: Reached idetape_chrdev_open\n");
 #endif /* IDETAPE_DEBUG_LOG */

drivers/scsi/st.c

@@ -1001,6 +1001,7 @@ static int st_open(struct inode *inode, struct file *filp)
 	int dev = TAPE_NR(inode);
 	char *name;
 
+	nonseekable_open(inode, filp);
 	write_lock(&st_dev_arr_lock);
 	if (dev >= st_dev_max || scsi_tapes == NULL ||
 	    ((STp = scsi_tapes[dev]) == NULL)) {
@@ -1203,7 +1204,7 @@ static int st_release(struct inode *inode, struct file *filp)
 }
 
 /* The checks common to both reading and writing */
-static ssize_t rw_checks(Scsi_Tape *STp, struct file *filp, size_t count, loff_t *ppos)
+static ssize_t rw_checks(Scsi_Tape *STp, struct file *filp, size_t count)
 {
 	ssize_t retval = 0;
 
@@ -1218,12 +1219,6 @@ static ssize_t rw_checks(Scsi_Tape *STp, struct file *filp, size_t count, loff_t
 		goto out;
 	}
 
-	if (ppos != &filp->f_pos) {
-		/* "A request was outside the capabilities of the device." */
-		retval = (-ENXIO);
-		goto out;
-	}
-
 	if (STp->ready != ST_READY) {
 		if (STp->ready == ST_NO_TAPE)
 			retval = (-ENOMEDIUM);
@@ -1367,7 +1362,7 @@ st_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 	if (down_interruptible(&STp->lock))
 		return -ERESTARTSYS;
 
-	retval = rw_checks(STp, filp, count, ppos);
+	retval = rw_checks(STp, filp, count);
 	if (retval || count == 0)
 		goto out;
 
@@ -1833,7 +1828,7 @@ st_read(struct file *filp, char __user *buf, size_t count, loff_t * ppos)
 	if (down_interruptible(&STp->lock))
 		return -ERESTARTSYS;
 
-	retval = rw_checks(STp, filp, count, ppos);
+	retval = rw_checks(STp, filp, count);
 	if (retval || count == 0)
 		goto out;