diff --git a/drivers/ahci/ahci.c b/drivers/ahci/ahci.c
index a695702ee..b3dfc59f9 100644
--- a/drivers/ahci/ahci.c
+++ b/drivers/ahci/ahci.c
@@ -243,7 +243,7 @@ static ssize_t ahci_transfer(devminor_t minor, int do_write, u64_t position,
 static struct device *ahci_part(devminor_t minor);
 static void ahci_alarm(clock_t stamp);
 static int ahci_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-	cp_grant_id_t grant);
+	cp_grant_id_t grant, endpoint_t user_endpt);
 static void ahci_intr(unsigned int mask);
 static int ahci_device(devminor_t minor, device_id_t *id);
 static struct port_state *ahci_get_port(devminor_t minor);
@@ -2632,7 +2632,7 @@ static ssize_t ahci_transfer(devminor_t minor, int do_write, u64_t position,
  *				ahci_ioctl				     *
  *===========================================================================*/
 static int ahci_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-	cp_grant_id_t grant)
+	cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	/* Process I/O control requests.
 	 */
diff --git a/drivers/at_wini/at_wini.c b/drivers/at_wini/at_wini.c
index dc87257cb..e33ed009b 100644
--- a/drivers/at_wini/at_wini.c
+++ b/drivers/at_wini/at_wini.c
@@ -157,7 +157,7 @@ static void w_need_reset(void);
 static void ack_irqs(unsigned int);
 static int w_do_close(devminor_t minor);
 static int w_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-	cp_grant_id_t grant);
+	cp_grant_id_t grant, endpoint_t user_endpt);
 static void w_hw_int(unsigned int irqs);
 static int com_simple(struct command *cmd);
 static void w_timeout(void);
@@ -2212,7 +2212,7 @@ int do_dma;
  *				w_ioctl					     *
  *===========================================================================*/
 static int w_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-	cp_grant_id_t grant)
+	cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	int r, timeout, prev, count;
 	struct command cmd;
diff --git a/drivers/cat24c256/cat24c256.c b/drivers/cat24c256/cat24c256.c
index fbd4eb081..5a97ca091 100644
--- a/drivers/cat24c256/cat24c256.c
+++ b/drivers/cat24c256/cat24c256.c
@@ -34,7 +34,7 @@ static int cat24c256_blk_close(devminor_t minor);
 static ssize_t cat24c256_blk_transfer(devminor_t minor, int do_write,
     u64_t pos, endpoint_t endpt, iovec_t * iov, unsigned int count, int flags);
 static int cat24c256_blk_ioctl(devminor_t minor, unsigned int request,
-    endpoint_t endpt, cp_grant_id_t grant);
+    endpoint_t endpt, cp_grant_id_t grant, endpoint_t user_endpt);
 static struct device *cat24c256_blk_part(devminor_t minor);
 static void cat24c256_blk_other(message * m, int ipc_status);
 
@@ -210,7 +210,7 @@ cat24c256_blk_transfer(devminor_t minor, int do_write, u64_t pos64,
 
 static int
 cat24c256_blk_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-    cp_grant_id_t grant)
+    cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	log_trace(&log, "cat24c256_blk_ioctl(%d)\n", minor);
 	/* no supported ioctls for this device */
diff --git a/drivers/fbd/fbd.c b/drivers/fbd/fbd.c
index 9b0dbdc4d..6e86eb934 100644
--- a/drivers/fbd/fbd.c
+++ b/drivers/fbd/fbd.c
@@ -20,7 +20,7 @@ static int fbd_close(devminor_t minor);
 static int fbd_transfer(devminor_t minor, int do_write, u64_t position,
 	endpoint_t endpt, iovec_t *iov, unsigned int nr_req, int flags);
 static int fbd_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-	cp_grant_id_t grant);
+	cp_grant_id_t grant, endpoint_t user_endpt);
 
 /* Variables. */
 static char *fbd_buf;			/* scratch buffer */
@@ -190,7 +190,7 @@ static int fbd_close(devminor_t UNUSED(minor))
  *				fbd_ioctl				     *
  *===========================================================================*/
 static int fbd_ioctl(devminor_t UNUSED(minor), unsigned int request,
-	endpoint_t endpt, cp_grant_id_t grant)
+	endpoint_t endpt, cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	/* Handle an I/O control request. */
 	cp_grant_id_t gid;
@@ -215,6 +215,7 @@ static int fbd_ioctl(devminor_t UNUSED(minor), unsigned int request,
 	m.BDEV_MINOR = driver_minor;
 	m.BDEV_REQUEST = request;
 	m.BDEV_GRANT = gid;
+	m.BDEV_USER = NONE;
 	m.BDEV_ID = 0;
 
 	if ((r = sendrec(driver_endpt, &m)) != OK)
diff --git a/drivers/filter/driver.c b/drivers/filter/driver.c
index 131ccbd78..478c3e597 100644
--- a/drivers/filter/driver.c
+++ b/drivers/filter/driver.c
@@ -60,6 +60,7 @@ static int driver_open(int which)
 	msg.BDEV_MINOR = driver[which].minor;
 	msg.BDEV_REQUEST = DIOCGETP;
 	msg.BDEV_GRANT = gid;
+	msg.BDEV_USER = NONE;
 	msg.BDEV_ID = 0;
 
 	r = sendrec(driver[which].endpt, &msg);
diff --git a/drivers/memory/memory.c b/drivers/memory/memory.c
index 3c8e5bdef..45bf5bdb7 100644
--- a/drivers/memory/memory.c
+++ b/drivers/memory/memory.c
@@ -58,7 +58,7 @@ static int m_block_transfer(devminor_t minor, int do_write, u64_t position,
 static int m_block_open(devminor_t minor, int access);
 static int m_block_close(devminor_t minor);
 static int m_block_ioctl(devminor_t minor, unsigned int request, endpoint_t
-	endpt, cp_grant_id_t grant);
+	endpt, cp_grant_id_t grant, endpoint_t user_endpt);
 
 /* Entry points to the CHARACTER part of this driver. */
 static struct chardriver m_cdtab = {
@@ -512,7 +512,7 @@ static int m_block_close(devminor_t minor)
  *				m_block_ioctl				     *
  *===========================================================================*/
 static int m_block_ioctl(devminor_t minor, unsigned int request,
-	endpoint_t endpt, cp_grant_id_t grant)
+	endpoint_t endpt, cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 /* I/O controls for the block devices of the memory driver. Currently there is
  * one I/O control specific to the memory driver:
diff --git a/drivers/mmc/mmcblk.c b/drivers/mmc/mmcblk.c
index 71ce29a1d..8a6353f54 100644
--- a/drivers/mmc/mmcblk.c
+++ b/drivers/mmc/mmcblk.c
@@ -49,8 +49,8 @@ static int block_transfer(devminor_t minor,
     u64_t position,
     endpoint_t endpt, iovec_t * iov, unsigned int nr_req, int flags);
 
-static int block_ioctl(devminor_t minor,
-    unsigned int request, endpoint_t endpt, cp_grant_id_t grant);
+static int block_ioctl(devminor_t minor, unsigned int request,
+	endpoint_t endpt, cp_grant_id_t grant, endpoint_t user_endpt);
 static struct device *block_part(devminor_t minor);
 
 /* System even handling */
@@ -435,8 +435,8 @@ block_transfer(
  *				block_ioctl		                     *
  *===========================================================================*/
 static int
-block_ioctl(devminor_t minor,
-    unsigned int request, endpoint_t endpt, cp_grant_id_t grant)
+block_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
+    cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	/* IOCTL handling */
 	struct sd_slot *slot;
diff --git a/drivers/tda19988/tda19988.c b/drivers/tda19988/tda19988.c
index 551ee4f9e..8e2225a52 100644
--- a/drivers/tda19988/tda19988.c
+++ b/drivers/tda19988/tda19988.c
@@ -168,7 +168,7 @@ static int tda19988_blk_close(devminor_t minor);
 static ssize_t tda19988_blk_transfer(devminor_t minor, int do_write, u64_t pos,
     endpoint_t endpt, iovec_t * iov, unsigned int count, int flags);
 static int tda19988_blk_ioctl(devminor_t minor, unsigned int request,
-    endpoint_t endpt, cp_grant_id_t grant);
+    endpoint_t endpt, cp_grant_id_t grant, endpoint_t user_endpt);
 static struct device *tda19988_blk_part(devminor_t minor);
 static void tda19988_blk_other(message * m, int ipc_status);
 
@@ -315,7 +315,7 @@ tda19988_blk_transfer(devminor_t minor, int do_write, u64_t pos64,
 
 static int
 tda19988_blk_ioctl(devminor_t minor, unsigned int request, endpoint_t endpt,
-    cp_grant_id_t grant)
+    cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	log_trace(&log, "tda19988_blk_ioctl(%d)\n", minor);
 	/* no supported ioctls for this device */
diff --git a/drivers/virtio_blk/virtio_blk.c b/drivers/virtio_blk/virtio_blk.c
index cef52ee46..5a13619c6 100644
--- a/drivers/virtio_blk/virtio_blk.c
+++ b/drivers/virtio_blk/virtio_blk.c
@@ -83,7 +83,7 @@ static ssize_t virtio_blk_transfer(devminor_t minor, int write, u64_t position,
 				   endpoint_t endpt, iovec_t *iovec,
 				   unsigned int cnt, int flags);
 static int virtio_blk_ioctl(devminor_t minor, unsigned int req,
-			    endpoint_t endpt, cp_grant_id_t grant);
+	endpoint_t endpt, cp_grant_id_t grant, endpoint_t user_endpt);
 static struct device * virtio_blk_part(devminor_t minor);
 static void virtio_blk_geometry(devminor_t minor, struct part_geom *entry);
 static void virtio_blk_device_intr(void);
@@ -376,7 +376,7 @@ virtio_blk_transfer(devminor_t minor, int write, u64_t position,
 
 static int
 virtio_blk_ioctl(devminor_t minor, unsigned int req, endpoint_t endpt,
-		 cp_grant_id_t grant)
+		 cp_grant_id_t grant, endpoint_t UNUSED(user_endpt))
 {
 	switch (req) {
 
diff --git a/include/minix/bdev.h b/include/minix/bdev.h
index dce412a4c..0aca2887a 100644
--- a/include/minix/bdev.h
+++ b/include/minix/bdev.h
@@ -16,7 +16,8 @@ extern ssize_t bdev_gather(dev_t dev, u64_t pos, iovec_t *vec, int count,
 	int flags);
 extern ssize_t bdev_scatter(dev_t dev, u64_t pos, iovec_t *vec, int count,
 	int flags);
-extern int bdev_ioctl(dev_t dev, int request, void *buf);
+extern int bdev_ioctl(dev_t dev, int request, void *buf,
+	endpoint_t user_endpt);
 
 /* Asynchronous API. */
 typedef int bdev_id_t;
@@ -36,7 +37,7 @@ extern bdev_id_t bdev_gather_asyn(dev_t dev, u64_t pos, iovec_t *vec,
 extern bdev_id_t bdev_scatter_asyn(dev_t dev, u64_t pos, iovec_t *vec,
 	int count, int flags, bdev_callback_t callback, bdev_param_t param);
 extern bdev_id_t bdev_ioctl_asyn(dev_t dev, int request, void *buf,
-	bdev_callback_t callback, bdev_param_t param);
+	endpoint_t user_endpt, bdev_callback_t callback, bdev_param_t param);
 
 extern int bdev_wait_asyn(bdev_id_t id);
 
diff --git a/include/minix/blockdriver.h b/include/minix/blockdriver.h
index 3bc058cf3..0c172182b 100644
--- a/include/minix/blockdriver.h
+++ b/include/minix/blockdriver.h
@@ -20,7 +20,7 @@ struct blockdriver {
   ssize_t (*bdr_transfer)(devminor_t minor, int do_write, u64_t pos,
 	  endpoint_t endpt, iovec_t *iov, unsigned int count, int flags);
   int (*bdr_ioctl)(devminor_t minor, unsigned int request, endpoint_t endpt,
-	  cp_grant_id_t grant);
+	  cp_grant_id_t grant, endpoint_t user_endpt);
   void (*bdr_cleanup)(void);
   struct device *(*bdr_part)(devminor_t minor);
   void (*bdr_geometry)(devminor_t minor, struct part_geom *part);
diff --git a/include/minix/com.h b/include/minix/com.h
index 520836722..2bf4be570 100644
--- a/include/minix/com.h
+++ b/include/minix/com.h
@@ -1325,6 +1325,7 @@
 #define BDEV_COUNT	m10_i2	/* number of bytes or elements in transfer */
 #define BDEV_GRANT	m10_i3	/* grant ID of buffer or vector */
 #define BDEV_FLAGS	m10_i4	/* transfer flags */
+#define BDEV_USER	m10_i4	/* user endpoint requesting I/O control */
 #define BDEV_ID		m10_l1	/* opaque request ID */
 #define BDEV_POS_LO	m10_l2	/* transfer position (low bits) */
 #define BDEV_POS_HI	m10_l3	/* transfer position (high bits) */
diff --git a/lib/libbdev/bdev.c b/lib/libbdev/bdev.c
index f8eafb9c9..b4037f963 100644
--- a/lib/libbdev/bdev.c
+++ b/lib/libbdev/bdev.c
@@ -305,7 +305,8 @@ ssize_t bdev_scatter(dev_t dev, u64_t pos, iovec_t *vec, int count, int flags)
   return bdev_vrdwt(BDEV_SCATTER, dev, pos, vec, count, flags);
 }
 
-static int bdev_ioctl_setup(dev_t dev, int request, void *buf, message *m)
+static int bdev_ioctl_setup(dev_t dev, int request, void *buf,
+  endpoint_t user_endpt, message *m)
 {
 /* Set up an I/O control request.
  */
@@ -339,6 +340,7 @@ static int bdev_ioctl_setup(dev_t dev, int request, void *buf, message *m)
   m->BDEV_MINOR = minor(dev);
   m->BDEV_REQUEST = request;
   m->BDEV_GRANT = grant;
+  m->BDEV_USER = user_endpt;
 
   return OK;
 }
@@ -351,7 +353,7 @@ static void bdev_ioctl_cleanup(const message *m)
   cpf_revoke(m->BDEV_GRANT);
 }
 
-int bdev_ioctl(dev_t dev, int request, void *buf)
+int bdev_ioctl(dev_t dev, int request, void *buf, endpoint_t user_endpt)
 {
 /* Perform a synchronous I/O control request.
  */
@@ -359,7 +361,7 @@ int bdev_ioctl(dev_t dev, int request, void *buf)
   int r, driver_tries = 0;
 
   do {
-	if ((r = bdev_ioctl_setup(dev, request, buf, &m)) != OK)
+	if ((r = bdev_ioctl_setup(dev, request, buf, user_endpt, &m)) != OK)
 		break;
 
 	r = bdev_sendrec(dev, &m);
@@ -496,7 +498,7 @@ bdev_id_t bdev_scatter_asyn(dev_t dev, u64_t pos, iovec_t *vec, int count,
 }
 
 bdev_id_t bdev_ioctl_asyn(dev_t dev, int request, void *buf,
-	bdev_callback_t callback, bdev_param_t param)
+	endpoint_t user_endpt, bdev_callback_t callback, bdev_param_t param)
 {
 /* Perform an asynchronous I/O control request.
  */
@@ -506,7 +508,8 @@ bdev_id_t bdev_ioctl_asyn(dev_t dev, int request, void *buf,
   if ((call = bdev_call_alloc(1)) == NULL)
 	return ENOMEM;
 
-  if ((r = bdev_ioctl_setup(dev, request, buf, &call->msg)) != OK) {
+  if ((r = bdev_ioctl_setup(dev, request, buf, user_endpt,
+		&call->msg)) != OK) {
 	bdev_call_free(call);
 
 	return r;
@@ -623,7 +626,8 @@ int bdev_restart_asyn(bdev_call_t *call)
 	bdev_ioctl_cleanup(&call->msg);
 
 	r = bdev_ioctl_setup(call->dev, call->msg.BDEV_REQUEST,
-		(char *) call->vec[0].iov_addr, &call->msg);
+		(char *) call->vec[0].iov_addr, call->msg.BDEV_USER,
+		&call->msg);
 
 	break;
 
diff --git a/lib/libblockdriver/driver.c b/lib/libblockdriver/driver.c
index 04a095df0..aadc9b0a3 100644
--- a/lib/libblockdriver/driver.c
+++ b/lib/libblockdriver/driver.c
@@ -2,7 +2,7 @@
  *
  * Block drivers support the following requests. Message format m10 is used.
  * Field names are prefixed with BDEV_. Separate field names are used for the
- * "access" and "request" fields.
+ * "access", "request", and "user" fields.
  *
  *    m_type        MINOR     COUNT     GRANT   FLAGS    ID   POS_LO POS_HI
  * +--------------+--------+----------+-------+-------+------+------+------+
@@ -18,7 +18,7 @@
  * |--------------+--------+----------+-------+-------+------+------+------|
  * | BDEV_SCATTER | minor  | elements | grant | flags |  id  |  position   |
  * |--------------+--------+----------+-------+-------+------+------+------|
- * | BDEV_IOCTL   | minor  | request  | grant | flags |  id  |      |      |
+ * | BDEV_IOCTL   | minor  | request  | grant | user  |  id  |      |      |
  * -------------------------------------------------------------------------
  *
  * The following reply message is used for all requests.
@@ -320,11 +320,13 @@ static int do_ioctl(struct blockdriver *bdp, message *mp)
   dev_t minor;
   unsigned int request;
   cp_grant_id_t grant;
+  endpoint_t user_endpt;
   int r;
 
   minor = mp->BDEV_MINOR;
   request = mp->BDEV_REQUEST;
   grant = mp->BDEV_GRANT;
+  user_endpt = mp->BDEV_USER;
 
   switch (request) {
   case BIOCTRACEBUF:
@@ -348,7 +350,8 @@ static int do_ioctl(struct blockdriver *bdp, message *mp)
 	/* fall-through */
   default:
 	if (bdp->bdr_ioctl)
-		r = (*bdp->bdr_ioctl)(minor, request, mp->m_source, grant);
+		r = (*bdp->bdr_ioctl)(minor, request, mp->m_source, grant,
+			user_endpt);
 	else
 		r = ENOTTY;
   }
diff --git a/servers/vfs/device.c b/servers/vfs/device.c
index 7e7111c36..090f3aa36 100644
--- a/servers/vfs/device.c
+++ b/servers/vfs/device.c
@@ -185,6 +185,7 @@ static int bdev_ioctl(dev_t dev, endpoint_t proc_e, int req, void *buf)
   dev_mess.BDEV_MINOR = minor_dev;
   dev_mess.BDEV_REQUEST = req;
   dev_mess.BDEV_GRANT = gid;
+  dev_mess.BDEV_USER = proc_e;
   dev_mess.BDEV_ID = 0;
 
   /* Call the task. */
diff --git a/test/blocktest/blocktest.c b/test/blocktest/blocktest.c
index ee0f149e7..8f12f25bf 100644
--- a/test/blocktest/blocktest.c
+++ b/test/blocktest/blocktest.c
@@ -1090,10 +1090,9 @@ static int vir_ioctl(dev_t minor, int req, void *ptr, ssize_t exp,
 	memset(&m, 0, sizeof(m));
 	m.m_type = BDEV_IOCTL;
 	m.BDEV_MINOR = minor;
-	m.BDEV_POS_LO = 0L;
-	m.BDEV_POS_HI = 0L;
 	m.BDEV_REQUEST = req;
 	m.BDEV_GRANT = grant;
+	m.BDEV_USER = NONE;
 	m.BDEV_ID = lrand48();
 
 	r = sendrec_driver(&m, exp, res);