Illumos #3112, #3113, #3114

3112 ztest does not honor ZFS_DEBUG
3113 ztest should use watchpoints to protect frozen arc bufs
3114 some leaked nvlists in zfsdev_ioctl

Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matt Amdur <Matt.Amdur@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <chris.siden@delphix.com>
Approved by: Eric Schrock <eric.schrock@delphix.com>

References:
  https://www.illumos.org/issues/3112
  https://www.illumos.org/issues/3113
  https://www.illumos.org/issues/3114
  illumos/illumos-gate@cd1c8b85eb

The /proc/self/cmd watchpoint interface is specific to Solaris.
Therefore, the #3113 implementation was reworked to use the more
portable mprotect(2) system call.  When the pages are watched they
are marked read-only for protection.  Any write to the protected
address range immediately trigger a SIGSEGV.  The pages are marked
writable again when they are unwatched.

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1489

include/sys/arc.h

@@ -136,6 +136,7 @@ int arc_buf_size(arc_buf_t *buf);
 void arc_release(arc_buf_t *buf, void *tag);
 int arc_released(arc_buf_t *buf);
 int arc_has_callback(arc_buf_t *buf);
+void arc_buf_sigsegv(int sig, siginfo_t *si, void *unused);
 void arc_buf_freeze(arc_buf_t *buf);
 void arc_buf_thaw(arc_buf_t *buf);
 boolean_t arc_buf_eviction_needed(arc_buf_t *buf);
@@ -183,6 +184,10 @@ extern int zfs_write_limit_shift;
 extern unsigned long zfs_write_limit_max;
 extern kmutex_t zfs_write_limit_lock;
 
+#ifndef _KERNEL
+extern boolean_t arc_watch;
+#endif
+
 #ifdef	__cplusplus
 }
 #endif