tools/kvm_stat: add logfile support

index e83fc8e868f4..d6cced4e1ef4 100755
@@ -1500,8 +1500,7 @@ class StdFormat(object):
     def get_banner(self):
         return self._banner
 
-    @staticmethod
-    def get_statline(keys, s):
+    def get_statline(self, keys, s):
         res = ''
         for key in keys:
             res += ' %9d' % s[key].delta

@@ -1517,8 +1516,7 @@ class CSVFormat(object):
     def get_banner(self):
         return self._banner
 
-    @staticmethod
-    def get_statline(keys, s):
+    def get_statline(self, keys, s):
         return reduce(lambda res, key: "{},{!s}".format(res, s[key].delta),
                       keys, '')
 

@@ -1527,14 +1525,21 @@ def log(stats, opts, frmt, keys):
     """Prints statistics as reiterating key block, multiple value blocks."""
     line = 0
     banner_repeat = 20
+    banner_printed = False
+
     while True:
         try:
             time.sleep(opts.set_delay)
-            if line % banner_repeat == 0:
+            if line % banner_repeat == 0 and not banner_printed:
                 print(frmt.get_banner())
-            print(datetime.now().strftime("%Y-%m-%d %H:%M:%S") +
-                  frmt.get_statline(keys, stats.get()))
-            line += 1
+                banner_printed = True
+            values = stats.get()
+            if (not opts.skip_zero_records or
+                any(values[k].delta != 0 for k in keys)):
+                print(datetime.now().strftime("%Y-%m-%d %H:%M:%S") +
+                      frmt.get_statline(keys, values))
+                line += 1
+                banner_printed = False
         except KeyboardInterrupt:
             break
 

@@ -1655,9 +1660,16 @@ Press any other key to refresh statistics immediately.
                            default=False,
                            help='retrieve statistics from tracepoints',
                            )
+    argparser.add_argument('-z', '--skip-zero-records',
+                           action='store_true',
+                           default=False,
+                           help='omit records with all zeros in logging mode',
+                           )
     options = argparser.parse_args()
     if options.csv and not options.log:
         sys.exit('Error: Option -c/--csv requires -l/--log')
+    if options.skip_zero_records and not options.log:
+        sys.exit('Error: Option -z/--skip-zero-records requires -l/--log')
     try:
         # verify that we were passed a valid regex up front
         re.compile(options.fields)

index a97ded2aedad..24296dccc00a 100644
@@ -104,6 +104,10 @@ OPTIONS
 --tracepoints::
         retrieve statistics from tracepoints
 
+*z*::
+--skip-zero-records::
+        omit records with all zeros in logging mode
+
 SEE ALSO
 --------
 'perf'(1), 'trace-cmd'(1)

index d6cced4e1ef4..d199a3694be8 100755
@@ -32,6 +32,7 @@ import resource
 import struct
 import re
 import subprocess
+import signal
 from collections import defaultdict, namedtuple
 from functools import reduce
 from datetime import datetime

@@ -228,6 +229,8 @@ IOCTL_NUMBERS = {
     'RESET':       0x00002403,
 }
 
+signal_received = False
+
 ENCODING = locale.getpreferredencoding(False)
 TRACE_FILTER = re.compile(r'^[^\(]*$')
 

@@ -1523,26 +1526,64 @@ class CSVFormat(object):
 
 def log(stats, opts, frmt, keys):
     """Prints statistics as reiterating key block, multiple value blocks."""
+    global signal_received
     line = 0
     banner_repeat = 20
-    banner_printed = False
-
+    f = None
+
+    def do_banner(opts):
+        nonlocal f
+        if opts.log_to_file:
+            if not f:
+                try:
+                     f = open(opts.log_to_file, 'a')
+                except (IOError, OSError):
+                    sys.exit("Error: Could not open file: %s" %
+                             opts.log_to_file)
+                if isinstance(frmt, CSVFormat) and f.tell() != 0:
+                    return
+        print(frmt.get_banner(), file=f or sys.stdout)
+
+    def do_statline(opts, values):
+        statline = datetime.now().strftime("%Y-%m-%d %H:%M:%S") + \
+                   frmt.get_statline(keys, values)
+        print(statline, file=f or sys.stdout)
+
+    do_banner(opts)
+    banner_printed = True
     while True:
         try:
             time.sleep(opts.set_delay)
-            if line % banner_repeat == 0 and not banner_printed:
-                print(frmt.get_banner())
+            if signal_received:
+                banner_printed = True
+                line = 0
+                f.close()
+                do_banner(opts)
+                signal_received = False
+            if (line % banner_repeat == 0 and not banner_printed and
+                not (opts.log_to_file and isinstance(frmt, CSVFormat))):
+                do_banner(opts)
                 banner_printed = True
             values = stats.get()
             if (not opts.skip_zero_records or
                 any(values[k].delta != 0 for k in keys)):
-                print(datetime.now().strftime("%Y-%m-%d %H:%M:%S") +
-                      frmt.get_statline(keys, values))
+                do_statline(opts, values)
                 line += 1
                 banner_printed = False
         except KeyboardInterrupt:
             break
 
+    if opts.log_to_file:
+        f.close()
+
+
+def handle_signal(sig, frame):
+    global signal_received
+
+    signal_received = True
+
+    return
+
 
 def is_delay_valid(delay):
     """Verify delay is in valid value range."""

@@ -1615,7 +1656,7 @@ Press any other key to refresh statistics immediately.
     argparser.add_argument('-c', '--csv',
                            action='store_true',
                            default=False,
-                           help='log in csv format - requires option -l/--log',
+                           help='log in csv format - requires option -l/-L',
                            )
     argparser.add_argument('-d', '--debugfs',
                            action='store_true',

@@ -1643,6 +1684,11 @@ Press any other key to refresh statistics immediately.
                            default=False,
                            help='run in logging mode (like vmstat)',
                            )
+    argparser.add_argument('-L', '--log-to-file',
+                           type=str,
+                           metavar='FILE',
+                           help="like '--log', but logging to a file"
+                           )
     argparser.add_argument('-p', '--pid',
                            type=int,
                            default=0,

@@ -1666,10 +1712,10 @@ Press any other key to refresh statistics immediately.
                            help='omit records with all zeros in logging mode',
                            )
     options = argparser.parse_args()
-    if options.csv and not options.log:
+    if options.csv and not (options.log or options.log_to_file):
         sys.exit('Error: Option -c/--csv requires -l/--log')
-    if options.skip_zero_records and not options.log:
-        sys.exit('Error: Option -z/--skip-zero-records requires -l/--log')
+    if options.skip_zero_records and not (options.log or options.log_to_file):
+        sys.exit('Error: Option -z/--skip-zero-records requires -l/-L')
     try:
         # verify that we were passed a valid regex up front
         re.compile(options.fields)

@@ -1749,7 +1795,9 @@ def main():
         sys.stdout.write('  ' + '\n  '.join(sorted(set(event_list))) + '\n')
         sys.exit(0)
 
-    if options.log:
+    if options.log or options.log_to_file:
+        if options.log_to_file:
+            signal.signal(signal.SIGHUP, handle_signal)
         keys = sorted(stats.get().keys())
         if options.csv:
             frmt = CSVFormat(keys)

index 24296dccc00a..feaf46451e83 100644
@@ -65,8 +65,10 @@ OPTIONS
 	run in batch mode for one second
 
 -c::
---csv=<file>::
-        log in csv format - requires option -l/--log
+--csv::
+        log in csv format. Requires option -l/--log or -L/--log-to-file.
+        When used with option -L/--log-to-file, the header is only ever
+        written to start of file to preserve the format.
 
 -d::
 --debugfs::

@@ -92,6 +94,11 @@ OPTIONS
 --log::
         run in logging mode (like vmstat)
 
+
+-L<file>::
+--log-to-file=<file>::
+        like -l/--log, but logging to a file. Appends to existing files.
+
 -p<pid>::
 --pid=<pid>::
 	limit statistics to one virtual machine (pid)

new file mode 100644
index 000000000000..71aabaffe779
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+[Unit]
+Description=Service that logs KVM kernel module trace events
+Before=qemu-kvm.service
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/kvm_stat -dtcz -s 10 -L /var/log/kvm_stat.csv
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=always
+SyslogIdentifier=kvm_stat
+SyslogLevel=debug
+
+[Install]
+WantedBy=multi-user.target