diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index 6a8ea0b..b83dd88 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -154,7 +154,7 @@ void scsi_req_enqueue(SCSIRequest *req)
     QTAILQ_INSERT_TAIL(&req->dev->requests, req, next);
 }
 
-void scsi_req_dequeue(SCSIRequest *req)
+static void scsi_req_dequeue(SCSIRequest *req)
 {
     trace_scsi_req_dequeue(req->dev->id, req->lun, req->tag);
     if (req->enqueued) {
@@ -398,6 +398,95 @@ int scsi_req_parse(SCSIRequest *req, uint8_t *buf)
     return 0;
 }
 
+/*
+ * Predefined sense codes
+ */
+
+/* No sense data available */
+const struct SCSISense sense_code_NO_SENSE = {
+    .key = NO_SENSE , .asc = 0x00 , .ascq = 0x00
+};
+
+/* LUN not ready, Manual intervention required */
+const struct SCSISense sense_code_LUN_NOT_READY = {
+    .key = NOT_READY, .asc = 0x04, .ascq = 0x03
+};
+
+/* LUN not ready, Medium not present */
+const struct SCSISense sense_code_NO_MEDIUM = {
+    .key = NOT_READY, .asc = 0x3a, .ascq = 0x00
+};
+
+/* Hardware error, internal target failure */
+const struct SCSISense sense_code_TARGET_FAILURE = {
+    .key = HARDWARE_ERROR, .asc = 0x44, .ascq = 0x00
+};
+
+/* Illegal request, invalid command operation code */
+const struct SCSISense sense_code_INVALID_OPCODE = {
+    .key = ILLEGAL_REQUEST, .asc = 0x20, .ascq = 0x00
+};
+
+/* Illegal request, LBA out of range */
+const struct SCSISense sense_code_LBA_OUT_OF_RANGE = {
+    .key = ILLEGAL_REQUEST, .asc = 0x21, .ascq = 0x00
+};
+
+/* Illegal request, Invalid field in CDB */
+const struct SCSISense sense_code_INVALID_FIELD = {
+    .key = ILLEGAL_REQUEST, .asc = 0x24, .ascq = 0x00
+};
+
+/* Illegal request, LUN not supported */
+const struct SCSISense sense_code_LUN_NOT_SUPPORTED = {
+    .key = ILLEGAL_REQUEST, .asc = 0x25, .ascq = 0x00
+};
+
+/* Command aborted, I/O process terminated */
+const struct SCSISense sense_code_IO_ERROR = {
+    .key = ABORTED_COMMAND, .asc = 0x00, .ascq = 0x06
+};
+
+/* Command aborted, I_T Nexus loss occurred */
+const struct SCSISense sense_code_I_T_NEXUS_LOSS = {
+    .key = ABORTED_COMMAND, .asc = 0x29, .ascq = 0x07
+};
+
+/* Command aborted, Logical Unit failure */
+const struct SCSISense sense_code_LUN_FAILURE = {
+    .key = ABORTED_COMMAND, .asc = 0x3e, .ascq = 0x01
+};
+
+/*
+ * scsi_build_sense
+ *
+ * Build a sense buffer
+ */
+int scsi_build_sense(SCSISense sense, uint8_t *buf, int len, int fixed)
+{
+    if (!fixed && len < 8) {
+        return 0;
+    }
+
+    memset(buf, 0, len);
+    if (fixed) {
+        /* Return fixed format sense buffer */
+        buf[0] = 0xf0;
+        buf[2] = sense.key;
+        buf[7] = 7;
+        buf[12] = sense.asc;
+        buf[13] = sense.ascq;
+        return MIN(len, 18);
+    } else {
+        /* Return descriptor format sense buffer */
+        buf[0] = 0x72;
+        buf[1] = sense.key;
+        buf[2] = sense.asc;
+        buf[3] = sense.ascq;
+        return 8;
+    }
+}
+
 static const char *scsi_command_name(uint8_t cmd)
 {
     static const char *names[] = {
diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
index 0921c62..a82753f 100644
--- a/hw/scsi-disk.c
+++ b/hw/scsi-disk.c
@@ -49,10 +49,6 @@ do { fprintf(stderr, "scsi-disk: " fmt , ## __VA_ARGS__); } while (0)
 
 typedef struct SCSIDiskState SCSIDiskState;
 
-typedef struct SCSISense {
-    uint8_t key;
-} SCSISense;
-
 typedef struct SCSIDiskReq {
     SCSIRequest req;
     /* ??? We should probably keep track of whether the data transfer is
@@ -109,24 +105,19 @@ static void scsi_disk_clear_sense(SCSIDiskState *s)
     memset(&s->sense, 0, sizeof(s->sense));
 }
 
-static void scsi_disk_set_sense(SCSIDiskState *s, uint8_t key)
-{
-    s->sense.key = key;
-}
-
-static void scsi_req_set_status(SCSIDiskReq *r, int status, int sense_code)
+static void scsi_req_set_status(SCSIDiskReq *r, int status, SCSISense sense)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
 
     r->req.status = status;
-    scsi_disk_set_sense(s, sense_code);
+    s->sense = sense;
 }
 
 /* Helper function for command completion.  */
-static void scsi_command_complete(SCSIDiskReq *r, int status, int sense)
+static void scsi_command_complete(SCSIDiskReq *r, int status, SCSISense sense)
 {
-    DPRINTF("Command complete tag=0x%x status=%d sense=%d\n",
-            r->req.tag, status, sense);
+    DPRINTF("Command complete tag=0x%x status=%d sense=%d/%d/%d\n",
+            r->req.tag, status, sense.key, sense.asc, sense.ascq);
     scsi_req_set_status(r, status, sense);
     scsi_req_complete(&r->req);
 }
@@ -180,7 +171,7 @@ static void scsi_read_data(SCSIRequest *req)
     }
     DPRINTF("Read sector_count=%d\n", r->sector_count);
     if (r->sector_count == 0) {
-        scsi_command_complete(r, GOOD, NO_SENSE);
+        scsi_command_complete(r, GOOD, SENSE_CODE(NO_SENSE));
         return;
     }
 
@@ -223,8 +214,13 @@ static int scsi_handle_rw_error(SCSIDiskReq *r, int error, int type)
         if (type == SCSI_REQ_STATUS_RETRY_READ) {
             scsi_req_data(&r->req, 0);
         }
-        scsi_command_complete(r, CHECK_CONDITION,
-                HARDWARE_ERROR);
+        if (error == ENOMEM) {
+            scsi_command_complete(r, CHECK_CONDITION,
+                                  SENSE_CODE(TARGET_FAILURE));
+        } else {
+            scsi_command_complete(r, CHECK_CONDITION,
+                                  SENSE_CODE(IO_ERROR));
+        }
         bdrv_mon_event(s->bs, BDRV_ACTION_REPORT, is_read);
     }
 
@@ -249,7 +245,7 @@ static void scsi_write_complete(void * opaque, int ret)
     r->sector += n;
     r->sector_count -= n;
     if (r->sector_count == 0) {
-        scsi_command_complete(r, GOOD, NO_SENSE);
+        scsi_command_complete(r, GOOD, SENSE_CODE(NO_SENSE));
     } else {
         len = r->sector_count * 512;
         if (len > SCSI_DMA_BUF_SIZE) {
@@ -276,7 +272,7 @@ static int scsi_write_data(SCSIRequest *req)
         r->req.aiocb = bdrv_aio_writev(s->bs, r->sector, &r->qiov, n,
                                    scsi_write_complete, r);
         if (r->req.aiocb == NULL) {
-            scsi_write_complete(r, -EIO);
+            scsi_write_complete(r, -ENOMEM);
         }
     } else {
         /* Invoke completion routine to fetch data from host.  */
@@ -314,7 +310,7 @@ static void scsi_dma_restart_bh(void *opaque)
             case SCSI_REQ_STATUS_RETRY_FLUSH:
                 ret = scsi_disk_emulate_command(r, r->iov.iov_base);
                 if (ret == 0) {
-                    scsi_command_complete(r, GOOD, NO_SENSE);
+                    scsi_command_complete(r, GOOD, SENSE_CODE(NO_SENSE));
                 }
             }
         }
@@ -813,19 +809,8 @@ static int scsi_disk_emulate_command(SCSIDiskReq *r, uint8_t *outbuf)
     case REQUEST_SENSE:
         if (req->cmd.xfer < 4)
             goto illegal_request;
-        memset(outbuf, 0, 4);
-        buflen = 4;
-        if (s->sense.key == NOT_READY && req->cmd.xfer >= 18) {
-            memset(outbuf, 0, 18);
-            buflen = 18;
-            outbuf[7] = 10;
-            /* asc 0x3a, ascq 0: Medium not present */
-            outbuf[12] = 0x3a;
-            outbuf[13] = 0;
-        }
-        outbuf[0] = 0xf0;
-        outbuf[1] = 0;
-        outbuf[2] = s->sense.key;
+        buflen = scsi_build_sense(s->sense, outbuf, req->cmd.xfer,
+                                  req->cmd.xfer > 13);
         scsi_disk_clear_sense(s);
         break;
     case INQUIRY:
@@ -963,17 +948,22 @@ static int scsi_disk_emulate_command(SCSIDiskReq *r, uint8_t *outbuf)
         }
         break;
     default:
-        goto illegal_request;
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(INVALID_OPCODE));
+        return -1;
     }
-    scsi_req_set_status(r, GOOD, NO_SENSE);
+    scsi_req_set_status(r, GOOD, SENSE_CODE(NO_SENSE));
     return buflen;
 
 not_ready:
-    scsi_command_complete(r, CHECK_CONDITION, NOT_READY);
+    if (!bdrv_is_inserted(s->bs)) {
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(NO_MEDIUM));
+    } else {
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(LUN_NOT_READY));
+    }
     return -1;
 
 illegal_request:
-    scsi_command_complete(r, CHECK_CONDITION, ILLEGAL_REQUEST);
+    scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(INVALID_FIELD));
     return -1;
 }
 
@@ -1000,7 +990,8 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
 
     if (scsi_req_parse(&r->req, buf) != 0) {
         BADF("Unsupported command length, command %x\n", command);
-        goto fail;
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(INVALID_OPCODE));
+        return 0;
     }
 #ifdef DEBUG_SCSI
     {
@@ -1015,8 +1006,11 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
     if (req->lun || buf[1] >> 5) {
         /* Only LUN 0 supported.  */
         DPRINTF("Unimplemented LUN %d\n", req->lun ? req->lun : buf[1] >> 5);
-        if (command != REQUEST_SENSE && command != INQUIRY)
-            goto fail;
+        if (command != REQUEST_SENSE && command != INQUIRY) {
+            scsi_command_complete(r, CHECK_CONDITION,
+                                  SENSE_CODE(LUN_NOT_SUPPORTED));
+            return 0;
+        }
     }
     switch (command) {
     case TEST_UNIT_READY:
@@ -1124,15 +1118,17 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *buf)
         break;
     default:
         DPRINTF("Unknown SCSI command (%2.2x)\n", buf[0]);
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(INVALID_OPCODE));
+        return 0;
     fail:
-        scsi_command_complete(r, CHECK_CONDITION, ILLEGAL_REQUEST);
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(INVALID_FIELD));
         return 0;
     illegal_lba:
-        scsi_command_complete(r, CHECK_CONDITION, HARDWARE_ERROR);
+        scsi_command_complete(r, CHECK_CONDITION, SENSE_CODE(LBA_OUT_OF_RANGE));
         return 0;
     }
     if (r->sector_count == 0 && r->iov.iov_len == 0) {
-        scsi_command_complete(r, GOOD, NO_SENSE);
+        scsi_command_complete(r, GOOD, SENSE_CODE(NO_SENSE));
     }
     len = r->sector_count * 512 + r->iov.iov_len;
     if (is_write) {
diff --git a/hw/scsi-generic.c b/hw/scsi-generic.c
index e1f8a8a..b934ba4 100644
--- a/hw/scsi-generic.c
+++ b/hw/scsi-generic.c
@@ -66,6 +66,19 @@ struct SCSIGenericState
     uint8_t senselen;
 };
 
+static void scsi_set_sense(SCSIGenericState *s, SCSISense sense)
+{
+    s->senselen = scsi_build_sense(sense, s->sensebuf, SCSI_SENSE_BUF_SIZE, 0);
+    s->driver_status = SG_ERR_DRIVER_SENSE;
+}
+
+static void scsi_clear_sense(SCSIGenericState *s)
+{
+    memset(s->sensebuf, 0, SCSI_SENSE_BUF_SIZE);
+    s->senselen = 0;
+    s->driver_status = 0;
+}
+
 static SCSIRequest *scsi_new_request(SCSIDevice *d, uint32_t tag, uint32_t lun)
 {
     SCSIRequest *req;
@@ -92,9 +105,22 @@ static void scsi_command_complete(void *opaque, int ret)
     if (s->driver_status & SG_ERR_DRIVER_SENSE)
         s->senselen = r->io_header.sb_len_wr;
 
-    if (ret != 0)
-        r->req.status = BUSY;
-    else {
+    if (ret != 0) {
+        switch (ret) {
+        case -EINVAL:
+            r->req.status = CHECK_CONDITION;
+            scsi_set_sense(s, SENSE_CODE(INVALID_FIELD));
+            break;
+        case -ENOMEM:
+            r->req.status = CHECK_CONDITION;
+            scsi_set_sense(s, SENSE_CODE(TARGET_FAILURE));
+            break;
+        default:
+            r->req.status = CHECK_CONDITION;
+            scsi_set_sense(s, SENSE_CODE(IO_ERROR));
+            break;
+        }
+    } else {
         if (s->driver_status & SG_ERR_DRIVER_TIMEOUT) {
             r->req.status = BUSY;
             BADF("Driver Timeout\n");
@@ -144,7 +170,7 @@ static int execute_command(BlockDriverState *bdrv,
     r->req.aiocb = bdrv_aio_ioctl(bdrv, SG_IO, &r->io_header, complete, r);
     if (r->req.aiocb == NULL) {
         BADF("execute_command: read failed !\n");
-        return -1;
+        return -ENOMEM;
     }
 
     return 0;
@@ -197,12 +223,14 @@ static void scsi_read_data(SCSIRequest *req)
                 r->buf[0], r->buf[1], r->buf[2], r->buf[3],
                 r->buf[4], r->buf[5], r->buf[6], r->buf[7]);
         scsi_req_data(&r->req, s->senselen);
+        /* Clear sensebuf after REQUEST_SENSE */
+        scsi_clear_sense(s);
         return;
     }
 
     ret = execute_command(s->bs, r, SG_DXFER_FROM_DEV, scsi_read_complete);
-    if (ret == -1) {
-        scsi_command_complete(r, -EINVAL);
+    if (ret < 0) {
+        scsi_command_complete(r, ret);
         return;
     }
 }
@@ -244,8 +272,8 @@ static int scsi_write_data(SCSIRequest *req)
     }
 
     ret = execute_command(s->bs, r, SG_DXFER_TO_DEV, scsi_write_complete);
-    if (ret == -1) {
-        scsi_command_complete(r, -EINVAL);
+    if (ret < 0) {
+        scsi_command_complete(r, ret);
         return 1;
     }
 
@@ -294,16 +322,7 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *cmd)
     if (cmd[0] != REQUEST_SENSE &&
         (req->lun != s->lun || (cmd[1] >> 5) != s->lun)) {
         DPRINTF("Unimplemented LUN %d\n", req->lun ? req->lun : cmd[1] >> 5);
-
-        s->sensebuf[0] = 0x70;
-        s->sensebuf[1] = 0x00;
-        s->sensebuf[2] = ILLEGAL_REQUEST;
-        s->sensebuf[3] = 0x00;
-        s->sensebuf[4] = 0x00;
-        s->sensebuf[5] = 0x00;
-        s->sensebuf[6] = 0x00;
-        s->senselen = 7;
-        s->driver_status = SG_ERR_DRIVER_SENSE;
+        scsi_set_sense(s, SENSE_CODE(LUN_NOT_SUPPORTED));
         r->req.status = CHECK_CONDITION;
         scsi_req_complete(&r->req);
         return 0;
@@ -311,8 +330,7 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *cmd)
 
     if (-1 == scsi_req_parse(&r->req, cmd)) {
         BADF("Unsupported command length, command %x\n", cmd[0]);
-        scsi_req_dequeue(&r->req);
-        scsi_req_unref(&r->req);
+        scsi_command_complete(r, -EINVAL);
         return 0;
     }
     scsi_req_fixup(&r->req);
@@ -336,8 +354,9 @@ static int32_t scsi_send_command(SCSIRequest *req, uint8_t *cmd)
         r->buflen = 0;
         r->buf = NULL;
         ret = execute_command(s->bs, r, SG_DXFER_NONE, scsi_command_complete);
-        if (ret == -1) {
-            scsi_command_complete(r, -EINVAL);
+        if (ret < 0) {
+            scsi_command_complete(r, ret);
+            return 0;
         }
         return 0;
     }
diff --git a/hw/scsi.h b/hw/scsi.h
index ee16638..61ab7c9 100644
--- a/hw/scsi.h
+++ b/hw/scsi.h
@@ -27,6 +27,12 @@ enum SCSIXferMode {
     SCSI_XFER_TO_DEV,    /*  WRITE, MODE_SELECT, ...         */
 };
 
+typedef struct SCSISense {
+    uint8_t key;
+    uint8_t asc;
+    uint8_t ascq;
+} SCSISense;
+
 struct SCSIRequest {
     SCSIBus           *bus;
     SCSIDevice        *dev;
@@ -104,10 +110,41 @@ SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, BlockDriverState *bdrv,
                                       int unit, bool removable);
 int scsi_bus_legacy_handle_cmdline(SCSIBus *bus);
 
+/*
+ * Predefined sense codes
+ */
+
+/* No sense data available */
+extern const struct SCSISense sense_code_NO_SENSE;
+/* LUN not ready, Manual intervention required */
+extern const struct SCSISense sense_code_LUN_NOT_READY;
+/* LUN not ready, Medium not present */
+extern const struct SCSISense sense_code_NO_MEDIUM;
+/* Hardware error, internal target failure */
+extern const struct SCSISense sense_code_TARGET_FAILURE;
+/* Illegal request, invalid command operation code */
+extern const struct SCSISense sense_code_INVALID_OPCODE;
+/* Illegal request, LBA out of range */
+extern const struct SCSISense sense_code_LBA_OUT_OF_RANGE;
+/* Illegal request, Invalid field in CDB */
+extern const struct SCSISense sense_code_INVALID_FIELD;
+/* Illegal request, LUN not supported */
+extern const struct SCSISense sense_code_LUN_NOT_SUPPORTED;
+/* Command aborted, I/O process terminated */
+extern const struct SCSISense sense_code_IO_ERROR;
+/* Command aborted, I_T Nexus loss occurred */
+extern const struct SCSISense sense_code_I_T_NEXUS_LOSS;
+/* Command aborted, Logical Unit failure */
+extern const struct SCSISense sense_code_LUN_FAILURE;
+
+#define SENSE_CODE(x) sense_code_ ## x
+
+int scsi_build_sense(SCSISense sense, uint8_t *buf, int len, int fixed);
+int scsi_sense_valid(SCSISense sense);
+
 SCSIRequest *scsi_req_alloc(size_t size, SCSIDevice *d, uint32_t tag, uint32_t lun);
 void scsi_req_enqueue(SCSIRequest *req);
 void scsi_req_free(SCSIRequest *req);
-void scsi_req_dequeue(SCSIRequest *req);
 SCSIRequest *scsi_req_ref(SCSIRequest *req);
 void scsi_req_unref(SCSIRequest *req);
 
