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trace: add ability to do simple printf logging via systemtap

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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>
This commit is contained in:
Daniel P. Berrangé 2019-01-23 12:00:16 +00:00 committed by Stefan Hajnoczi
parent 772f1b3721
commit 62dd1048c0
7 changed files with 467 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
MAINTAINERS
View File

@ -2017,6 +2017,7 @@ F: trace-events
F: qemu-option-trace.texi
F: scripts/tracetool.py
F: scripts/tracetool/
F: scripts/qemu-trace-stap*
F: docs/devel/tracing.txt
T: git https://github.com/stefanha/qemu.git tracing

10
Makefile
View File

@ -305,6 +305,9 @@ DOCS+=docs/qemu-cpu-models.7
ifdef CONFIG_VIRTFS
DOCS+=fsdev/virtfs-proxy-helper.1
endif
ifdef CONFIG_TRACE_SYSTEMTAP
DOCS+=scripts/qemu-trace-stap.1
endif
else
DOCS=
endif
@ -699,6 +702,9 @@ ifneq ($(TOOLS),)
$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man8"
$(INSTALL_DATA) qemu-nbd.8 "$(DESTDIR)$(mandir)/man8"
endif
ifdef CONFIG_TRACE_SYSTEMTAP
$(INSTALL_DATA) scripts/qemu-trace-stap.1 "$(DESTDIR)$(mandir)/man1"
endif
ifneq (,$(findstring qemu-ga,$(TOOLS)))
$(INSTALL_DATA) qemu-ga.8 "$(DESTDIR)$(mandir)/man8"
$(INSTALL_DATA) docs/interop/qemu-ga-ref.html "$(DESTDIR)$(qemu_docdir)"
@ -738,6 +744,9 @@ endif
ifneq ($(HELPERS-y),)
$(call install-prog,$(HELPERS-y),$(DESTDIR)$(libexecdir))
endif
ifdef CONFIG_TRACE_SYSTEMTAP
$(INSTALL_PROG) "scripts/qemu-trace-stap" $(DESTDIR)$(bindir)
endif
ifneq ($(BLOBS),)
set -e; for x in $(BLOBS); do \
$(INSTALL_DATA) $(SRC_PATH)/pc-bios/$$x "$(DESTDIR)$(qemu_datadir)"; \
@ -852,6 +861,7 @@ qemu-nbd.8: qemu-nbd.texi qemu-option-trace.texi
qemu-ga.8: qemu-ga.texi
docs/qemu-block-drivers.7: docs/qemu-block-drivers.texi
docs/qemu-cpu-models.7: docs/qemu-cpu-models.texi
scripts/qemu-trace-stap.1: scripts/qemu-trace-stap.texi
html: qemu-doc.html docs/interop/qemu-qmp-ref.html docs/interop/qemu-ga-ref.html
info: qemu-doc.info docs/interop/qemu-qmp-ref.info docs/interop/qemu-ga-ref.info

11
Makefile.target
View File

@ -45,7 +45,7 @@ config-target.h: config-target.h-timestamp
config-target.h-timestamp: config-target.mak
ifdef CONFIG_TRACE_SYSTEMTAP
stap: $(QEMU_PROG).stp-installed $(QEMU_PROG).stp $(QEMU_PROG)-simpletrace.stp
stap: $(QEMU_PROG).stp-installed $(QEMU_PROG).stp $(QEMU_PROG)-simpletrace.stp $(QEMU_PROG)-log.stp
ifdef CONFIG_USER_ONLY
TARGET_TYPE=user
@ -84,6 +84,14 @@ $(QEMU_PROG)-simpletrace.stp: $(BUILD_DIR)/trace-events-all $(tracetool-y)
--probe-prefix=qemu.$(TARGET_TYPE).$(TARGET_NAME) \
$< > $@,"GEN","$(TARGET_DIR)$(QEMU_PROG)-simpletrace.stp")
$(QEMU_PROG)-log.stp: $(BUILD_DIR)/trace-events-all $(tracetool-y)
$(call quiet-command,$(TRACETOOL) \
--group=all \
--format=log-stap \
--backends=$(TRACE_BACKENDS) \
--probe-prefix=qemu.$(TARGET_TYPE).$(TARGET_NAME) \
$< > $@,"GEN","$(TARGET_DIR)$(QEMU_PROG)-log.stp")
else
stap:
endif
@ -227,6 +235,7 @@ ifdef CONFIG_TRACE_SYSTEMTAP
$(INSTALL_DIR) "$(DESTDIR)$(qemu_datadir)/../systemtap/tapset"
$(INSTALL_DATA) $(QEMU_PROG).stp-installed "$(DESTDIR)$(qemu_datadir)/../systemtap/tapset/$(QEMU_PROG).stp"
$(INSTALL_DATA) $(QEMU_PROG)-simpletrace.stp "$(DESTDIR)$(qemu_datadir)/../systemtap/tapset/$(QEMU_PROG)-simpletrace.stp"
$(INSTALL_DATA) $(QEMU_PROG)-log.stp "$(DESTDIR)$(qemu_datadir)/../systemtap/tapset/$(QEMU_PROG)-log.stp"
endif
GENERATED_FILES += config-target.h

4
docs/devel/tracing.txt
View File

@ -317,6 +317,10 @@ probes:
--target-name x86_64 \
<trace-events-all >qemu.stp
To facilitate simple usage of systemtap where there merely needs to be printf
logging of certain probes, a helper script "qemu-trace-stap" is provided.
Consult its manual page for guidance on its usage.
== Trace event properties ==
Each event in the "trace-events-all" file can be prefixed with a space-separated

175
scripts/qemu-trace-stap Executable file
View File

@ -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()

140
scripts/qemu-trace-stap.texi Normal file
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@ -0,0 +1,140 @@
@example
@c man begin SYNOPSIS
@command{qemu-trace-stap} @var{GLOBAL-OPTIONS} @var{COMMAND} @var{COMMAND-OPTIONS} @var{ARGS...}
@c man end
@end example
@c man begin DESCRIPTION
The @command{qemu-trace-stap} program facilitates tracing of the execution
of QEMU emulators using SystemTap.
It is required to have the SystemTap runtime environment installed to use
this program, since it is a wrapper around execution of the @command{stap}
program.
@c man end
@c man begin OPTIONS
The following global options may be used regardless of which command
is executed:
@table @option
@item @var{--verbose}, @var{-v}
Display verbose information about command execution.
@end table
The following commands are valid:
@table @option
@item @var{list} @var{BINARY} @var{PATTERN...}
List all the probe names provided by @var{BINARY} that match
@var{PATTERN}.
If @var{BINARY} is not an absolute path, it will be located by searching
the directories listed in the @code{$PATH} environment variable.
@var{PATTERN} is a plain string that is used to filter the results of
this command. It may optionally contain a @code{*} wildcard to facilitate
matching multiple probes without listing each one explicitly. Multiple
@var{PATTERN} arguments may be given, causing listing of probes that match
any of the listed names. If no @var{PATTERN} is given, the all possible
probes will be listed.
For example, to list all probes available in the @command{qemu-system-x86_64}
binary:
@example
$ qemu-trace-stap list qemu-system-x86_64
@end example
To filter the list to only cover probes related to QEMU's cryptographic
subsystem, in a binary outside @code{$PATH}
@example
$ qemu-trace-stap list /opt/qemu/4.0.0/bin/qemu-system-x86_64 'qcrypto*'
@end example
@item @var{run} @var{OPTIONS} @var{BINARY} @var{PATTERN...}
Run a trace session, printing formatted output any time a process that is
executing @var{BINARY} triggers a probe matching @var{PATTERN}.
If @var{BINARY} is not an absolute path, it will be located by searching
the directories listed in the @code{$PATH} environment variable.
@var{PATTERN} is a plain string that matches a probe name shown by the
@var{list} command. It may optionally contain a @code{*} wildcard to
facilitate matching multiple probes without listing each one explicitly.
Multiple @var{PATTERN} arguments may be given, causing all matching probes
to be monitored. At least one @var{PATTERN} is required, since stap is not
capable of tracing all known QEMU probes concurrently without overflowing
its trace buffer.
Invocation of this command does not need to be synchronized with
invocation of the QEMU process(es). It will match probes on all
existing running processes and all future launched processes,
unless told to only monitor a specific process.
Valid command specific options are:
@table @option
@item @var{--pid=PID}, @var{-p PID}
Restrict the tracing session so that it only triggers for the process
identified by @code{PID}.
@end table
For example, to monitor all processes executing @command{qemu-system-x86_64}
as found on $PATH, displaying all I/O related probes:
@example
$ qemu-trace-stap run qemu-system-x86_64 'qio*'
@end example
To monitor only the QEMU process with PID 1732
@example
$ qemu-trace-stap run --pid=1732 qemu-system-x86_64 'qio*'
@end example
To monitor QEMU processes running an alternative binary outside of
@code{$PATH}, displaying verbose information about setup of the
tracing environment:
@example
$ qemu-trace-stap -v run /opt/qemu/4.0.0/qemu-system-x86_64 'qio*'
@end example
@end table
@c man end
@ignore
@setfilename qemu-trace-stap
@settitle QEMU SystemTap trace tool
@c man begin LICENSE
Copyright (C) 2019 Red Hat, Inc.
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.
@c man end
@c man begin SEEALSO
qemu(1), stap(1)
@c man end
@end ignore

127
scripts/tracetool/format/log_stap.py Normal file
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@ -0,0 +1,127 @@
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Generate .stp file that printfs log messages (DTrace with SystemTAP only).
"""
__author__ = "Daniel P. Berrange <berrange@redhat.com>"
__copyright__ = "Copyright (C) 2014-2019, Red Hat, Inc."
__license__ = "GPL version 2 or (at your option) any later version"
__maintainer__ = "Daniel Berrange"
__email__ = "berrange@redhat.com"
import re
from tracetool import out
from tracetool.backend.dtrace import binary, probeprefix
from tracetool.backend.simple import is_string
from tracetool.format.stap import stap_escape
def global_var_name(name):
return probeprefix().replace(".", "_") + "_" + name
STATE_SKIP = 0
STATE_LITERAL = 1
STATE_MACRO = 2
def c_macro_to_format(macro):
if macro.startswith("PRI"):
return macro[3]
if macro == "TARGET_FMT_plx":
return "%016x"
raise Exception("Unhandled macro '%s'" % macro)
def c_fmt_to_stap(fmt):
state = 0
bits = []
literal = ""
macro = ""
escape = 0;
for i in range(len(fmt)):
if fmt[i] == '\\':
if escape:
escape = 0
else:
escape = 1
if state != STATE_LITERAL:
raise Exception("Unexpected escape outside string literal")
literal = literal + fmt[i]
elif fmt[i] == '"' and not escape:
if state == STATE_LITERAL:
state = STATE_SKIP
bits.append(literal)
literal = ""
else:
if state == STATE_MACRO:
bits.append(c_macro_to_format(macro))
state = STATE_LITERAL
elif fmt[i] == ' ' or fmt[i] == '\t':
if state == STATE_MACRO:
bits.append(c_macro_to_format(macro))
macro = ""
state = STATE_SKIP
elif state == STATE_LITERAL:
literal = literal + fmt[i]
else:
escape = 0
if state == STATE_SKIP:
state = STATE_MACRO
if state == STATE_LITERAL:
literal = literal + fmt[i]
else:
macro = macro + fmt[i]
if state == STATE_MACRO:
bits.append(c_macro_to_format(macro))
elif state == STATE_LITERAL:
bits.append(literal)
fmt = re.sub("%(\d*)z(x|u|d)", "%\\1\\2", "".join(bits))
return fmt
def generate(events, backend, group):
out('/* This file is autogenerated by tracetool, do not edit. */',
'')
for event_id, e in enumerate(events):
if 'disable' in e.properties:
continue
out('probe %(probeprefix)s.log.%(name)s = %(probeprefix)s.%(name)s ?',
'{',
probeprefix=probeprefix(),
name=e.name)
# Get references to userspace strings
for type_, name in e.args:
name = stap_escape(name)
if is_string(type_):
out(' try {',
' arg%(name)s_str = %(name)s ? ' +
'user_string_n(%(name)s, 512) : "<null>"',
' } catch {}',
name=name)
# Determine systemtap's view of variable names
fields = ["pid()", "gettimeofday_ns()"]
for type_, name in e.args:
name = stap_escape(name)
if is_string(type_):
fields.append("arg" + name + "_str")
else:
fields.append(name)
# Emit the entire record in a single SystemTap printf()
arg_str = ', '.join(arg for arg in fields)
fmt_str = "%d@%d " + e.name + " " + c_fmt_to_stap(e.fmt) + "\\n"
out(' printf("%(fmt_str)s", %(arg_str)s)',
fmt_str=fmt_str, arg_str=arg_str)
out('}')
out()