Only in linux-2.6.8-rc2: .config
diff -ru linux-2.6.8-rc2.orig/drivers/block/paride/pcd.c linux-2.6.8-rc2/drivers/block/paride/pcd.c
--- linux-2.6.8-rc2.orig/drivers/block/paride/pcd.c	2004-08-02 19:58:12.000000000 -0500
+++ linux-2.6.8-rc2/drivers/block/paride/pcd.c	2004-08-02 20:17:37.000000000 -0500
@@ -259,7 +259,7 @@
 				unsigned cmd, unsigned long arg)
 {
 	struct pcd_unit *cd = inode->i_bdev->bd_disk->private_data;
-	return cdrom_ioctl(&cd->info, inode, cmd, arg);
+	return cdrom_ioctl(&cd->info, inode, file, cmd, arg);
 }
 
 static int pcd_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/cdrom.c linux-2.6.8-rc2/drivers/cdrom/cdrom.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/cdrom.c	2004-08-02 19:58:12.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/cdrom.c	2004-08-02 20:18:22.000000000 -0500
@@ -2065,15 +2065,18 @@
  * mmc_ioct().
  */
 int cdrom_ioctl(struct cdrom_device_info *cdi, struct inode *ip,
-		unsigned int cmd, unsigned long arg)
+		struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct cdrom_device_ops *cdo = cdi->ops;
 	int ret;
 
 	/* Try the generic SCSI command ioctl's first.. */
-	ret = scsi_cmd_ioctl(ip->i_bdev->bd_disk, cmd, (void __user *)arg);
-	if (ret != -ENOTTY)
-		return ret;
+	/* But only if the user has write access: open(,O_RDWR | O_NONBLOCK) */
+	if (file->f_mode & FMODE_WRITE) {
+		ret = scsi_cmd_ioctl(ip->i_bdev->bd_disk, cmd, (void __user *)arg);
+		if (ret != -ENOTTY)
+			return ret;
+	}
 
 	/* the first few commands do not deal with audio drive_info, but
 	   only with routines in cdrom device operations. */
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/cdu31a.c linux-2.6.8-rc2/drivers/cdrom/cdu31a.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/cdu31a.c	2004-06-16 00:19:42.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/cdu31a.c	2004-08-02 20:19:06.000000000 -0500
@@ -3179,7 +3179,7 @@
 static int scd_block_ioctl(struct inode *inode, struct file *file,
 				unsigned cmd, unsigned long arg)
 {
-	return cdrom_ioctl(&scd_info, inode, cmd, arg);
+	return cdrom_ioctl(&scd_info, inode, file, cmd, arg);
 }
 
 static int scd_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/cm206.c linux-2.6.8-rc2/drivers/cdrom/cm206.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/cm206.c	2004-06-16 00:20:03.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/cm206.c	2004-08-02 20:19:21.000000000 -0500
@@ -1363,7 +1363,7 @@
 static int cm206_block_ioctl(struct inode *inode, struct file *file,
 				unsigned cmd, unsigned long arg)
 {
-	return cdrom_ioctl(&cm206_info, inode, cmd, arg);
+	return cdrom_ioctl(&cm206_info, inode, file, cmd, arg);
 }
 
 static int cm206_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/mcd.c linux-2.6.8-rc2/drivers/cdrom/mcd.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/mcd.c	2004-06-16 00:19:37.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/mcd.c	2004-08-02 20:18:57.000000000 -0500
@@ -227,7 +227,7 @@
 static int mcd_block_ioctl(struct inode *inode, struct file *file,
 				unsigned cmd, unsigned long arg)
 {
-	return cdrom_ioctl(&mcd_info, inode, cmd, arg);
+	return cdrom_ioctl(&mcd_info, inode, file, cmd, arg);
 }
 
 static int mcd_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/mcdx.c linux-2.6.8-rc2/drivers/cdrom/mcdx.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/mcdx.c	2004-08-02 19:58:12.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/mcdx.c	2004-08-02 20:18:46.000000000 -0500
@@ -233,7 +233,7 @@
 				unsigned cmd, unsigned long arg)
 {
 	struct s_drive_stuff *p = inode->i_bdev->bd_disk->private_data;
-	return cdrom_ioctl(&p->info, inode, cmd, arg);
+	return cdrom_ioctl(&p->info, inode, file, cmd, arg);
 }
 
 static int mcdx_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/sbpcd.c linux-2.6.8-rc2/drivers/cdrom/sbpcd.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/sbpcd.c	2004-06-16 00:18:59.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/sbpcd.c	2004-08-02 20:18:37.000000000 -0500
@@ -5372,7 +5372,7 @@
 				unsigned cmd, unsigned long arg)
 {
 	struct sbpcd_drive *p = inode->i_bdev->bd_disk->private_data;
-	return cdrom_ioctl(p->sbpcd_infop, inode, cmd, arg);
+	return cdrom_ioctl(p->sbpcd_infop, inode, file, cmd, arg);
 }
 
 static int sbpcd_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/cdrom/viocd.c linux-2.6.8-rc2/drivers/cdrom/viocd.c
--- linux-2.6.8-rc2.orig/drivers/cdrom/viocd.c	2004-08-02 19:58:12.000000000 -0500
+++ linux-2.6.8-rc2/drivers/cdrom/viocd.c	2004-08-02 20:19:35.000000000 -0500
@@ -199,7 +199,7 @@
 		unsigned cmd, unsigned long arg)
 {
 	struct disk_info *di = inode->i_bdev->bd_disk->private_data;
-	return cdrom_ioctl(&di->viocd_info, inode, cmd, arg);
+	return cdrom_ioctl(&di->viocd_info, inode, file, cmd, arg);
 }
 
 static int viocd_blk_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/drivers/ide/ide-cd.c linux-2.6.8-rc2/drivers/ide/ide-cd.c
--- linux-2.6.8-rc2.orig/drivers/ide/ide-cd.c	2004-08-02 19:58:13.000000000 -0500
+++ linux-2.6.8-rc2/drivers/ide/ide-cd.c	2004-08-02 20:16:59.000000000 -0500
@@ -3394,7 +3394,7 @@
 	int err = generic_ide_ioctl(bdev, cmd, arg);
 	if (err == -EINVAL) {
 		struct cdrom_info *info = drive->driver_data;
-		err = cdrom_ioctl(&info->devinfo, inode, cmd, arg);
+		err = cdrom_ioctl(&info->devinfo, inode, file, cmd, arg);
 	}
 	return err;
 }
diff -ru linux-2.6.8-rc2.orig/drivers/scsi/sr.c linux-2.6.8-rc2/drivers/scsi/sr.c
--- linux-2.6.8-rc2.orig/drivers/scsi/sr.c	2004-08-02 19:58:24.000000000 -0500
+++ linux-2.6.8-rc2/drivers/scsi/sr.c	2004-08-02 20:17:23.000000000 -0500
@@ -504,7 +504,7 @@
                 case SCSI_IOCTL_GET_BUS_NUMBER:
                         return scsi_ioctl(sdev, cmd, (void __user *)arg);
 	}
-	return cdrom_ioctl(&cd->cdi, inode, cmd, arg);
+	return cdrom_ioctl(&cd->cdi, inode, file, cmd, arg);
 }
 
 static int sr_block_media_changed(struct gendisk *disk)
diff -ru linux-2.6.8-rc2.orig/include/linux/cdrom.h linux-2.6.8-rc2/include/linux/cdrom.h
--- linux-2.6.8-rc2.orig/include/linux/cdrom.h	2004-06-16 00:18:52.000000000 -0500
+++ linux-2.6.8-rc2/include/linux/cdrom.h	2004-08-02 20:20:09.000000000 -0500
@@ -985,7 +985,7 @@
 			struct file *fp);
 extern int cdrom_release(struct cdrom_device_info *cdi, struct file *fp);
 extern int cdrom_ioctl(struct cdrom_device_info *cdi, struct inode *ip,
-		unsigned int cmd, unsigned long arg);
+		struct file *file, unsigned int cmd, unsigned long arg);
 extern int cdrom_media_changed(struct cdrom_device_info *);
 
 extern int register_cdrom(struct cdrom_device_info *cdi);