[S390] vmur: reject open on z/VM reader files with status HOLD

If a reader file with HOLD status is at the top of the reader queue, currently
all read requests will return data of the second file in the queue. But the
semantics of vmur is that always the topmost file is read. With this fix
-EPERM is returned on open, if the topmost reader file is in HOLD status.

Signed-off-by: Michael Holzheu <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/char/vmur.c

···
 		rc = diag_read_next_file_info(&fcb, 0);
 		if (rc)
 			return rc;
-
+		/* if file is in hold status, we do not read it */
+		if (fcb.file_stat & (FLG_SYSTEM_HOLD | FLG_USER_HOLD))
+			return -EPERM;
 		/* open file on virtual reader	*/
 		buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 		if (!buf)

drivers/s390/char/vmur.h

···
 	char  rest[200];
 } __attribute__ ((packed));
 
-#define FLG_CP_DUMP 0x10
+#define FLG_SYSTEM_HOLD	0x04
+#define FLG_CP_DUMP	0x10
+#define FLG_USER_HOLD	0x20
 
 /*
  * A struct urdev is created for each ur device that is made available