15291 zfs-tests errno flaws exposed by 15220

*** 22,31 ****
--- 22,35 ----
  /*
   * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
+ /*
+  * Copyright 2022 MNX Cloud, Inc.
+  */
+ 
  #include "../file_common.h"
  
  static unsigned char bigbuffer[BIGBUFFERSIZE];
  
  /*
*** 64,76 ****
                  (void) printf("open %s failed %d\n", argv[1], errno);
                  exit(1);
          }
  
          do {
                  if ((n = read(bigfd, &bigbuffer, bigbuffersize)) == -1) {
                          (void) printf("read failed (%ld), %d\n", n, errno);
!                         exit(errno);
                  }
  
                  for (i = 0; i < n; i++) {
                          if (bigbuffer[i] != fillchar) {
                                  (void) printf("error %s: 0x%x != 0x%x)\n",
--- 68,83 ----
                  (void) printf("open %s failed %d\n", argv[1], errno);
                  exit(1);
          }
  
          do {
+                 int exitcode;
+ 
                  if ((n = read(bigfd, &bigbuffer, bigbuffersize)) == -1) {
+                         exitcode = errno;
                          (void) printf("read failed (%ld), %d\n", n, errno);
!                         exit(exitcode);
                  }
  
                  for (i = 0; i < n; i++) {
                          if (bigbuffer[i] != fillchar) {
                                  (void) printf("error %s: 0x%x != 0x%x)\n",