Handle broken pipes in arc_summary

Using a command similar to 'arc_summary.py | head' causes
a broken pipe exception. Gracefully exit in the case of a
broken pipe in arc_summary.py.

Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6965 
Closes #6969

cmd/arc_summary/arc_summary.py

@@ -47,6 +47,7 @@ import getopt
 import os
 import sys
 import time
+import errno
 
 from subprocess import Popen, PIPE
 from decimal import Decimal as D
@@ -55,6 +56,18 @@ show_tunable_descriptions = False
 alternate_tunable_layout = False
 
 
+def handle_Exception(ex_cls, ex, tb):
+    if ex is IOError:
+        if ex.errno == errno.EPIPE:
+            sys.exit()
+
+    if ex is KeyboardInterrupt:
+        sys.exit()
+
+
+sys.excepthook = handle_Exception
+
+
 def get_Kstat():
     """Collect information on the ZFS subsystem from the /proc virtual
     file system. The name "kstat" is a holdover from the Solaris utility

tests/zfs-tests/tests/functional/cli_user/misc/arc_summary_001_pos.ksh

@@ -37,4 +37,7 @@ while [[ $i -lt ${#args[*]} ]]; do
         ((i = i + 1))
 done
 
+log_must eval "arc_summary.py | head > /dev/null"
+log_must eval "arc_summary.py | head -1 > /dev/null"
+
 log_pass "arc_summary.py generates output and doesn't return an error code"