blkfront: properly fail packet requests

c/s 1036:f5635e334aa5 ("blkfront: forward unknown IOCTLs to
scsi_cmd_ioctl() for /dev/sdX") uncovered a problem in blkfront's
request handling: blk_pc_request()-s, among other sources resulting
from the handling of the SG_IO ioctl in scsi_cmd_ioctl(), must not be
passed to end_request() without prior adjustment: Neither is their
->hard_cur_sectors necessarily correct (potentially resulting in an
infinite loop), nor is ->errors ever getting set properly to reflect
the failure (sg_io() intentionally ignores the return value from
blk_execute_rq()).

As blktap2's internally created devices have the same deficiency, fix
this there too.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/blkfront/blkfront.c
+++ b/drivers/xen/blkfront/blkfront.c
@@ -709,6 +709,12 @@ void do_blkif_request(request_queue_t *r
 	while ((req = elv_next_request(rq)) != NULL) {
 		info = req->rq_disk->private_data;
 		if (!blk_fs_request(req)) {
+			if (blk_pc_request(req)) {
+				req->errors = (DID_ERROR << 16)
+					      | (DRIVER_INVALID << 24);
+				req->hard_cur_sectors = (req->data_len
+							 + 511) >> 9;
+			}
 			end_request(req, 0);
 			continue;
 		}
--- a/drivers/xen/blktap2/device.c
+++ b/drivers/xen/blktap2/device.c
@@ -3,6 +3,7 @@
 #include <linux/cdrom.h>
 #include <linux/hdreg.h>
 #include <linux/module.h>
+#include <scsi/scsi.h>
 #include <asm/tlbflush.h>
 
 #include <scsi/scsi.h>
@@ -825,6 +826,12 @@ blktap_device_run_queue(struct blktap *t
 
 	while ((req = elv_next_request(rq)) != NULL) {
 		if (!blk_fs_request(req)) {
+			if (blk_pc_request(req)) {
+				req->errors = (DID_ERROR << 16)
+					      | (DRIVER_INVALID << 24);
+				req->hard_cur_sectors = (req->data_len
+							 + 511) >> 9;
+			}
 			end_request(req, 0);
 			continue;
 		}
@@ -912,9 +919,16 @@ blktap_device_do_request(request_queue_t
 
 fail:
 	while ((req = elv_next_request(rq))) {
-		BTERR("device closed: failing secs %llu - %llu\n",
-		      (unsigned long long)req->sector,
-		      (unsigned long long)req->sector + req->nr_sectors);
+		if (blk_fs_request(req)) {
+			unsigned long long sec = req->sector;
+
+			BTERR("device closed: failing secs %#Lx-%#Lx\n",
+			      sec, sec + req->nr_sectors - 1);
+		} else if (blk_pc_request(req)) {
+			req->errors = (DID_ERROR << 16)
+				      | (DRIVER_INVALID << 24);
+			req->hard_cur_sectors = (req->data_len + 511) >> 9;
+		}
 		end_request(req, 0);
 	}
 }