trace: add ability to do simple printf logging via systemtap

The dtrace systemtap trace backend for QEMU is very powerful but it is
also somewhat unfriendly to users who aren't familiar with systemtap,
or who don't need its power right now.

  stap -e "....some strange script...."

The 'log' backend for QEMU by comparison is very crude but incredibly
easy to use:

 $ qemu -d trace:qio* ...some args...
 23266@1547735759.137292:qio_channel_socket_new Socket new ioc=0x563a8a39d400
 23266@1547735759.137305:qio_task_new Task new task=0x563a891d0570 source=0x563a8a39d400 func=0x563a86f1e6c0 opaque=0x563a89078000
 23266@1547735759.137326:qio_task_thread_start Task thread start task=0x563a891d0570 worker=0x563a86f1ce50 opaque=0x563a891d9d90
 23273@1547735759.137491:qio_task_thread_run Task thread run task=0x563a891d0570
 23273@1547735759.137503:qio_channel_socket_connect_sync Socket connect sync ioc=0x563a8a39d400 addr=0x563a891d9d90
 23273@1547735759.138108:qio_channel_socket_connect_fail Socket connect fail ioc=0x563a8a39d400

This commit introduces a way to do simple printf style logging of probe
points using systemtap. In particular it creates another set of tapsets,
one per emulator:

  /usr/share/systemtap/tapset/qemu-*-log.stp

These pre-define probe functions which simply call printf() on their
arguments. The printf() format string is taken from the normal
trace-events files, with a little munging to the format specifiers
to cope with systemtap's more restrictive syntax.

With this you can now do

 $ stap -e 'probe qemu.system.x86_64.log.qio*{}'
 22806@1547735341399856820 qio_channel_socket_new Socket new ioc=0x56135d1d7c00
 22806@1547735341399862570 qio_task_new Task new task=0x56135cd66eb0 source=0x56135d1d7c00 func=0x56135af746c0 opaque=0x56135bf06400
 22806@1547735341399865943 qio_task_thread_start Task thread start task=0x56135cd66eb0 worker=0x56135af72e50 opaque=0x56135c071d70
 22806@1547735341399976816 qio_task_thread_run Task thread run task=0x56135cd66eb0

We go one step further though and introduce a 'qemu-trace-stap' tool to
make this even easier

 $ qemu-trace-stap run qemu-system-x86_64 'qio*'
 22806@1547735341399856820 qio_channel_socket_new Socket new ioc=0x56135d1d7c00
 22806@1547735341399862570 qio_task_new Task new task=0x56135cd66eb0 source=0x56135d1d7c00 func=0x56135af746c0 opaque=0x56135bf06400
 22806@1547735341399865943 qio_task_thread_start Task thread start task=0x56135cd66eb0 worker=0x56135af72e50 opaque=0x56135c071d70
 22806@1547735341399976816 qio_task_thread_run Task thread run task=0x56135cd66eb0

This tool is clever in that it will automatically change the
SYSTEMTAP_TAPSET env variable to point to the directory containing the
right set of probes for the QEMU binary path you give it. This is useful
if you have QEMU installed in /usr but are trying to test and trace a
binary in /home/berrange/usr/qemu-git. In that case you'd do

 $ qemu-trace-stap run /home/berrange/usr/qemu-git/bin/qemu-system-x86_64 'qio*'

And it'll make sure /home/berrange/usr/qemu-git/share/systemtap/tapset
is used for the trace session

The 'qemu-trace-stap' script takes a verbose arg so you can understand
what it is running

 $ qemu-trace-stap run /home/berrange/usr/qemu-git/bin/qemu-system-x86_64 'qio*'
 Using tapset dir '/home/berrange/usr/qemu-git/share/systemtap/tapset' for binary '/home/berrange/usr/qemu-git/bin/qemu-system-x86_64'
 Compiling script 'probe qemu.system.x86_64.log.qio* {}'
 Running script, <Ctrl>-c to quit
 ...trace output...

It can enable multiple probes at once

 $ qemu-trace-stap run qemu-system-x86_64 'qio*' 'qcrypto*' 'buffer*'

By default it monitors all existing running processes and all future
launched proceses. This can be restricted to a specific PID using the
--pid arg

 $ qemu-trace-stap run --pid 2532 qemu-system-x86_64 'qio*'

Finally if you can't remember what probes are valid it can tell you

 $ qemu-trace-stap list qemu-system-x86_64
 ahci_check_irq
 ahci_cmd_done
 ahci_dma_prepare_buf
 ahci_dma_prepare_buf_fail
 ahci_dma_rw_buf
 ahci_irq_lower
 ...snip...

Or list just those matching a prefix pattern

 $ qemu-trace-stap list -v qemu-system-x86_64 'qio*'
 Using tapset dir '/home/berrange/usr/qemu-git/share/systemtap/tapset' for binary '/home/berrange/usr/qemu-git/bin/qemu-system-x86_64'
 Listing probes with name 'qemu.system.x86_64.log.qio*'
 qio_channel_command_abort
 qio_channel_command_new_pid
 qio_channel_command_new_spawn
 qio_channel_command_wait
 qio_channel_file_new_fd
 ...snip...

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20190123120016.4538-5-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 175 insertions, 0 deletions

diff --git a/scripts/qemu-trace-stap b/scripts/qemu-trace-stap
new file mode 100755
index 0000000..91d1051
--- /dev/null
+++ b/scripts/qemu-trace-stap
@@ -0,0 +1,175 @@
+#!/usr/bin/python
+# -*- python -*-
+#
+# Copyright (C) 2019 Red Hat, Inc
+#
+# QEMU SystemTap Trace Tool
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import print_function
+
+import argparse
+import copy
+import os.path
+import re
+import subprocess
+import sys
+
+
+def probe_prefix(binary):
+    dirname, filename = os.path.split(binary)
+    return re.sub("-", ".", filename) + ".log"
+
+
+def which(binary):
+    for path in os.environ["PATH"].split(os.pathsep):
+        if os.path.exists(os.path.join(path, binary)):
+                return os.path.join(path, binary)
+
+    print("Unable to find '%s' in $PATH" % binary)
+    sys.exit(1)
+
+
+def tapset_dir(binary):
+    dirname, filename = os.path.split(binary)
+    if dirname == '':
+        thisfile = which(binary)
+    else:
+        thisfile = os.path.realpath(binary)
+        if not os.path.exists(thisfile):
+            print("Unable to find '%s'" % thisfile)
+            sys.exit(1)
+
+    basedir = os.path.split(thisfile)[0]
+    tapset = os.path.join(basedir, "..", "share", "systemtap", "tapset")
+    return os.path.realpath(tapset)
+
+
+def tapset_env(tapset_dir):
+    tenv = copy.copy(os.environ)
+    tenv["SYSTEMTAP_TAPSET"] = tapset_dir
+    return tenv
+
+def cmd_run(args):
+    prefix = probe_prefix(args.binary)
+    tapsets = tapset_dir(args.binary)
+
+    if args.verbose:
+        print("Using tapset dir '%s' for binary '%s'" % (tapsets, args.binary))
+
+    probes = []
+    for probe in args.probes:
+        probes.append("probe %s.%s {}" % (prefix, probe))
+    if len(probes) == 0:
+        print("At least one probe pattern must be specified")
+        sys.exit(1)
+
+    script = " ".join(probes)
+    if args.verbose:
+        print("Compiling script '%s'" % script)
+        script = """probe begin { print("Running script, <Ctrl>-c to quit\\n") } """ + script
+
+    # We request an 8MB buffer, since the stap default 1MB buffer
+    # can be easily overflowed by frequently firing QEMU traces
+    stapargs = ["stap", "-s", "8"]
+    if args.pid is not None:
+        stapargs.extend(["-x", args.pid])
+    stapargs.extend(["-e", script])
+    subprocess.call(stapargs, env=tapset_env(tapsets))
+
+
+def cmd_list(args):
+    tapsets = tapset_dir(args.binary)
+
+    if args.verbose:
+        print("Using tapset dir '%s' for binary '%s'" % (tapsets, args.binary))
+
+    def print_probes(verbose, name):
+        prefix = probe_prefix(args.binary)
+        offset = len(prefix) + 1
+        script = prefix + "." + name
+
+        if verbose:
+            print("Listing probes with name '%s'" % script)
+        proc = subprocess.Popen(["stap", "-l", script],
+                                stdout=subprocess.PIPE, env=tapset_env(tapsets))
+        out, err = proc.communicate()
+        if proc.returncode != 0:
+            print("No probes found, are the tapsets installed in %s" % tapset_dir(args.binary))
+            sys.exit(1)
+
+        for line in out.splitlines():
+            if line.startswith(prefix):
+                print("%s" % line[offset:])
+
+    if len(args.probes) == 0:
+        print_probes(args.verbose, "*")
+    else:
+        for probe in args.probes:
+            print_probes(args.verbose, probe)
+
+
+def main():
+    parser = argparse.ArgumentParser(description="QEMU SystemTap trace tool")
+    parser.add_argument("-v", "--verbose", help="Print verbose progress info",
+                        action='store_true')
+
+    subparser = parser.add_subparsers(help="commands")
+    subparser.required = True
+    subparser.dest = "command"
+
+    runparser = subparser.add_parser("run", help="Run a trace session",
+                                     formatter_class=argparse.RawDescriptionHelpFormatter,
+                                     epilog="""
+
+To watch all trace points on the qemu-system-x86_64 binary:
+
+   %(argv0)s run qemu-system-x86_64
+
+To only watch the trace points matching the qio* and qcrypto* patterns
+
+   %(argv0)s run qemu-system-x86_64 'qio*' 'qcrypto*'
+""" % {"argv0": sys.argv[0]})
+    runparser.set_defaults(func=cmd_run)
+    runparser.add_argument("--pid", "-p", dest="pid",
+                           help="Restrict tracing to a specific process ID")
+    runparser.add_argument("binary", help="QEMU system or user emulator binary")
+    runparser.add_argument("probes", help="Probe names or wildcards",
+                           nargs=argparse.REMAINDER)
+
+    listparser = subparser.add_parser("list", help="List probe points",
+                                      formatter_class=argparse.RawDescriptionHelpFormatter,
+                                      epilog="""
+
+To list all trace points on the qemu-system-x86_64 binary:
+
+   %(argv0)s list qemu-system-x86_64
+
+To only list the trace points matching the qio* and qcrypto* patterns
+
+   %(argv0)s list qemu-system-x86_64 'qio*' 'qcrypto*'
+""" % {"argv0": sys.argv[0]})
+    listparser.set_defaults(func=cmd_list)
+    listparser.add_argument("binary", help="QEMU system or user emulator binary")
+    listparser.add_argument("probes", help="Probe names or wildcards",
+                            nargs=argparse.REMAINDER)
+
+    args = parser.parse_args()
+
+    args.func(args)
+    sys.exit(0)
+
+if __name__ == '__main__':
+    main()