qemu-e2k/scripts/qemu-trace-stap.texi

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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>
2019-01-23 13:00:16 +01:00
@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