[S390] vmur: add "top of queue" sanity check for reader open

If the z/VM reader is already open, it can happen that after opening the
Linux reader device, not the topmost file is processed. According the
semantics of the Linux z/VM unit record device driver, always the topmost
file has to be processed. With this fix an error is returned if that is
not the case.

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 7 insertions, 1 deletions

diff --git a/drivers/s390/char/vmur.c b/drivers/s390/char/vmur.c
index 04395c0f99d8..a9d58629e795 100644
--- a/drivers/s390/char/vmur.c
+++ b/drivers/s390/char/vmur.c
@@ -565,9 +565,14 @@ static int verify_device(struct urdev *urd)
                         return -ENOMEM;
                 rc = diag_read_file(urd->dev_id.devno, buf);
                 kfree(buf);
-
                 if ((rc != 0) && (rc != -ENODATA)) /* EOF does not hurt */
                         return rc;
+                /* check if the file on top of the queue is open now */
+                rc = diag_read_next_file_info(&fcb, 0);
+                if (rc)
+                        return rc;
+                if (!(fcb.file_stat & FLG_IN_USE))
+                        return -EMFILE;
                 return 0;
         default:
                 return -ENOTSUPP;
diff --git a/drivers/s390/char/vmur.h b/drivers/s390/char/vmur.h
index 522a9dfaa275..2b3c564e0472 100644
--- a/drivers/s390/char/vmur.h
+++ b/drivers/s390/char/vmur.h
@@ -53,6 +53,7 @@ struct file_control_block {
 #define FLG_SYSTEM_HOLD 0x04
 #define FLG_CP_DUMP     0x10
 #define FLG_USER_HOLD   0x20
+#define FLG_IN_USE      0x80
 
 /*
  * A struct urdev is created for each ur device that is made available