[PATCH] tools/kvm_stat: fix termination behavior when not on a terminal

[Claudio Fontana <cfontana@suse.de>]

For the -l and -L options (logging mode), replace the use of the
KeyboardInterrupt exception to gracefully terminate in favor
of handling the SIGINT and SIGTERM signals.

This allows the program to be run from scripts and still be
signaled to gracefully terminate without an interactive terminal.

Before this change, something like this script:

kvm_stat -p 85896 -d -t -s 1 -c -L kvm_stat_85896.csv &
sleep 10
pkill -TERM -P $$

would yield an empty log:
-rw-r--r-- 1 root root     0 Aug  7 16:17 kvm_stat_85896.csv

after this commit:
-rw-r--r-- 1 root root 13466 Aug  7 16:57 kvm_stat_85896.csv

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Cc: Dario Faggioli <dfaggioli@suse.com>
Cc: Fabiano Rosas <farosas@suse.de>
---
 tools/kvm/kvm_stat/kvm_stat     | 64 ++++++++++++++++-----------------
 tools/kvm/kvm_stat/kvm_stat.txt | 12 +++++++
 2 files changed, 44 insertions(+), 32 deletions(-)

diff --git a/tools/kvm/kvm_stat/kvm_stat b/tools/kvm/kvm_stat/kvm_stat
index 15bf00e79e3f..2cf2da3ed002 100755
--- a/tools/kvm/kvm_stat/kvm_stat
+++ b/tools/kvm/kvm_stat/kvm_stat
@@ -297,8 +297,6 @@ IOCTL_NUMBERS = {
     'RESET':       0x00002403,
 }
 
-signal_received = False
-
 ENCODING = locale.getpreferredencoding(False)
 TRACE_FILTER = re.compile(r'^[^\(]*$')
 
@@ -1598,7 +1596,19 @@ class CSVFormat(object):
 
 def log(stats, opts, frmt, keys):
     """Prints statistics as reiterating key block, multiple value blocks."""
-    global signal_received
+    signal_received = defaultdict(bool)
+
+    def handle_signal(sig, frame):
+        nonlocal signal_received
+        signal_received[sig] = True
+        return
+
+
+    signal.signal(signal.SIGINT, handle_signal)
+    signal.signal(signal.SIGTERM, handle_signal)
+    if opts.log_to_file:
+        signal.signal(signal.SIGHUP, handle_signal)
+
     line = 0
     banner_repeat = 20
     f = None
@@ -1624,39 +1634,31 @@ def log(stats, opts, frmt, keys):
     do_banner(opts)
     banner_printed = True
     while True:
-        try:
-            time.sleep(opts.set_delay)
-            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)):
-                do_statline(opts, values)
-                line += 1
-                banner_printed = False
-        except KeyboardInterrupt:
+        time.sleep(opts.set_delay)
+        # Do not use the KeyboardInterrupt exception, because we may be running without a terminal
+        if (signal_received[signal.SIGINT] or signal_received[signal.SIGTERM]):
             break
+        if signal_received[signal.SIGHUP]:
+            banner_printed = True
+            line = 0
+            f.close()
+            do_banner(opts)
+            signal_received[signal.SIGHUP] = 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)):
+            do_statline(opts, values)
+            line += 1
+            banner_printed = False
 
     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."""
     msg = None
@@ -1869,8 +1871,6 @@ def main():
         sys.exit(0)
 
     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)
diff --git a/tools/kvm/kvm_stat/kvm_stat.txt b/tools/kvm/kvm_stat/kvm_stat.txt
index 3a9f2037bd23..4a99a111a93c 100644
--- a/tools/kvm/kvm_stat/kvm_stat.txt
+++ b/tools/kvm/kvm_stat/kvm_stat.txt
@@ -115,6 +115,18 @@ OPTIONS
 --skip-zero-records::
         omit records with all zeros in logging mode
 
+
+SIGNALS
+-------
+when kvm_stat is running in logging mode (either with -l or with -L),
+it handles the following signals:
+
+SIGHUP - closes and reopens the log file (-L only), then continues.
+
+SIGINT - closes the log file and terminates.
+SIGTERM - closes the log file and terminates.
+
+
 SEE ALSO
 --------
 'perf'(1), 'trace-cmd'(1)
-- 
2.26.2