2013-05-03 14:25:37 +00:00
|
|
|
<?xml version="1.0" encoding="UTF-8"?>
|
|
|
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
|
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
2010-05-25 13:14:46 +00:00
|
|
|
<body>
|
|
|
|
|
<h1>Spawning processes / commands from libvirt drivers</h1>
|
|
|
|
|
|
|
|
|
|
<ul id="toc"></ul>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This page describes the usage of libvirt APIs for
|
|
|
|
|
spawning processes / commands from libvirt drivers.
|
|
|
|
|
All code is required to use these APIs
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h2><a name="posix">Problems with standard POSIX APIs</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The POSIX specification includes a number of APIs for
|
|
|
|
|
spawning processes / commands, but they suffer from
|
|
|
|
|
a number of flaws
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li><code>fork+exec</code>: The lowest & most flexible
|
2011-02-04 18:16:35 +00:00
|
|
|
level, but very hard to use correctly / safely. It
|
|
|
|
|
is easy to leak file descriptors, have unexpected
|
|
|
|
|
signal handler behaviour and not handle edge cases.
|
|
|
|
|
Furthermore, it is not portable to mingw.
|
|
|
|
|
</li>
|
2010-05-25 13:14:46 +00:00
|
|
|
<li><code>system</code>: Convenient if you don't care
|
2011-02-04 18:16:35 +00:00
|
|
|
about capturing command output, but has the serious
|
|
|
|
|
downside that the command string is interpreted by
|
|
|
|
|
the shell. This makes it very dangerous to use, because
|
|
|
|
|
improperly validated user input can lead to exploits
|
|
|
|
|
via shell meta characters.
|
2010-05-25 13:14:46 +00:00
|
|
|
</li>
|
|
|
|
|
<li><code>popen</code>: Inherits the flaws of
|
2011-02-04 18:16:35 +00:00
|
|
|
<code>system</code>, and has no option for bi-directional
|
|
|
|
|
communication.
|
2010-05-25 13:14:46 +00:00
|
|
|
</li>
|
|
|
|
|
<li><code>posix_spawn</code>: A half-way house between
|
2011-02-04 18:16:35 +00:00
|
|
|
simplicity of system() and the flexibility of fork+exec.
|
|
|
|
|
It does not allow for a couple of important features
|
|
|
|
|
though, such as running a hook between the fork+exec
|
|
|
|
|
stage, or closing all open file descriptors.</li>
|
2010-05-25 13:14:46 +00:00
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Due to the problems mentioned with each of these,
|
|
|
|
|
libvirt driver code <strong>must not use</strong> any
|
|
|
|
|
of the above APIs. Historically libvirt provided a
|
|
|
|
|
higher level API known as virExec. This was wrapper
|
|
|
|
|
around fork+exec, in a similar style to posix_spawn,
|
|
|
|
|
but with a few more features.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This wrapper still suffered from a number of problems.
|
|
|
|
|
Handling command cleanup via waitpid() is overly
|
|
|
|
|
complex & error prone for most usage. Building up the
|
|
|
|
|
argv[] + env[] string arrays is quite cumbersome and
|
|
|
|
|
error prone, particularly wrt memory leak / OOM handling.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h2><a name="api">The libvirt command execution API</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
There is now a high level API that provides a safe and
|
|
|
|
|
flexible way to spawn commands, which prevents the most
|
|
|
|
|
common errors & is easy to code against. This
|
2015-09-15 09:15:06 +00:00
|
|
|
code is provided in the <code>src/util/vircommand.h</code>
|
|
|
|
|
header which can be imported using <code>#include "vircommand.h"</code>
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3><a name="initial">Defining commands in libvirt</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The first step is to declare what command is to be
|
|
|
|
|
executed. The command name can be either a fully
|
|
|
|
|
qualified path, or a bare command name. In the latter
|
|
|
|
|
case it will be resolved wrt the <code>$PATH</code>
|
|
|
|
|
environment variable.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandPtr cmd = virCommandNew("/usr/bin/dnsmasq");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
There is no need to check for allocation failure after
|
|
|
|
|
<code>virCommandNew</code>. This will be detected and
|
|
|
|
|
reported at a later time.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3><a name="args">Adding arguments to the command</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
There are a number of APIs for adding arguments to a
|
|
|
|
|
command. To add a direct string arg
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddArg(cmd, "-strict-order");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
If an argument takes an attached value of the form
|
|
|
|
|
<code>-arg=val</code>, then this can be done using
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddArgPair(cmd, "--conf-file", "/etc/dnsmasq.conf");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
If an argument needs to be formatted as if by
|
|
|
|
|
<code>printf</code>:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddArgFormat(cmd, "%d", count);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
To add a entire NULL terminated array of arguments in one go,
|
|
|
|
|
there are two options.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
const char *const args[] = {
|
|
|
|
|
"--strict-order", "--except-interface", "lo", NULL
|
|
|
|
|
};
|
|
|
|
|
virCommandAddArgSet(cmd, args);
|
|
|
|
|
virCommandAddArgList(cmd, "--domain", "localdomain", NULL);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This can also be done at the time of initial construction of
|
|
|
|
|
the <code>virCommandPtr</code> object:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
const char *const args[] = {
|
|
|
|
|
"/usr/bin/dnsmasq",
|
|
|
|
|
"--strict-order", "--except-interface",
|
|
|
|
|
"lo", "--domain", "localdomain", NULL
|
|
|
|
|
};
|
|
|
|
|
virCommandPtr cmd1 = virCommandNewArgs(cmd, args);
|
|
|
|
|
virCommandPtr cmd2 = virCommandNewArgList("/usr/bin/dnsmasq",
|
|
|
|
|
"--domain", "localdomain", NULL);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="env">Setting up the environment</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
By default a command will inherit all environment variables
|
|
|
|
|
from the current process. Generally this is not desirable
|
|
|
|
|
and a customized environment will be more suitable. Any
|
|
|
|
|
customization done via the following APIs will prevent
|
|
|
|
|
inheritance of any existing environment variables unless
|
|
|
|
|
explicitly allowed. The first step is usually to pass through
|
|
|
|
|
a small number of variables from the current process.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddEnvPassCommon(cmd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This has now set up a clean environment for the child, passing
|
|
|
|
|
through <code>PATH</code>, <code>LD_PRELOAD</code>,
|
|
|
|
|
<code>LD_LIBRARY_PATH</code>, <code>HOME</code>,
|
|
|
|
|
<code>USER</code>, <code>LOGNAME</code> and <code>TMPDIR</code>.
|
|
|
|
|
Furthermore it will explicitly set <code>LC_ALL=C</code> to
|
|
|
|
|
avoid unexpected localization of command output. Further
|
|
|
|
|
variables can be passed through from parent explicitly:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddEnvPass(cmd, "DISPLAY");
|
|
|
|
|
virCommandAddEnvPass(cmd, "XAUTHORITY");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
To define an environment variable in the child with an
|
|
|
|
|
separate key / value:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddEnvPair(cmd, "TERM", "xterm");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
If the key/value pair is pre-formatted in the right
|
|
|
|
|
format, it can be set directly
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandAddEnvString(cmd, "TERM=xterm");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="misc">Miscellaneous other options</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Normally the spawned command will retain the current
|
|
|
|
|
process and process group as its parent. If the current
|
|
|
|
|
process dies, the child will then (usually) be terminated
|
|
|
|
|
too. If this cleanup is not desired, then the command
|
|
|
|
|
should be marked as daemonized:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandDaemonize(cmd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
When daemonizing a command, the PID visible from the
|
|
|
|
|
caller will be that of the intermediate process, not
|
|
|
|
|
the actual damonized command. If the PID of the real
|
|
|
|
|
command is required then a pidfile can be requested
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandSetPidFile(cmd, "/var/run/dnsmasq.pid");
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This PID file is guaranteed to be written before
|
|
|
|
|
the intermediate process exits.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3><a name="privs">Reducing command privileges</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Normally a command will inherit all privileges of
|
|
|
|
|
the current process. To restrict what a command can
|
|
|
|
|
do, it is possible to request that all its capabilities
|
|
|
|
|
are cleared. With this done it will only be able to
|
|
|
|
|
access resources for which it has explicit DAC permissions
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandClearCaps(cmd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="fds">Managing file handles</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
To prevent unintended resource leaks to child processes, the
|
|
|
|
|
child defaults to closing all open file handles, and setting
|
|
|
|
|
stdin/out/err to <code>/dev/null</code>. It is possible to
|
|
|
|
|
allow an open file handle to be passed into the child, while
|
|
|
|
|
controlling whether that handle remains open in the parent or
|
|
|
|
|
guaranteeing that the handle will be closed in the parent after
|
2010-12-06 23:36:34 +00:00
|
|
|
virCommandRun, virCommandRunAsync, or virCommandFree.
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
int sharedfd = open("cmd.log", "w+");
|
|
|
|
|
int childfd = open("conf.txt", "r");
|
|
|
|
|
virCommandPassFD(cmd, sharedfd, 0);
|
|
|
|
|
virCommandPassFD(cmd, childfd,
|
|
|
|
|
VIR_COMMAND_PASS_FD_CLOSE_PARENT);
|
|
|
|
|
if (VIR_CLOSE(sharedfd) < 0)
|
|
|
|
|
goto cleanup;
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
With this, both file descriptors sharedfd and childfd in the
|
|
|
|
|
current process remain open as the same file descriptors in the
|
|
|
|
|
child. Meanwhile, after the child is spawned, sharedfd remains
|
2010-12-06 23:36:34 +00:00
|
|
|
open in the parent, while childfd is closed.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
For stdin/out/err it is sometimes necessary to map a file
|
|
|
|
|
handle. If a mapped file handle is a pipe fed or consumed by
|
|
|
|
|
the caller, then the caller should use virCommandDaemonize or
|
|
|
|
|
virCommandRunAsync rather than virCommandRun to avoid deadlock
|
|
|
|
|
(mapping a regular file is okay with virCommandRun). To attach
|
|
|
|
|
file descriptor 7 in the current process to stdin in the child:
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandSetInputFD(cmd, 7);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Equivalently to redirect stdout or stderr in the child,
|
|
|
|
|
pass in a pointer to the desired handle
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
int outfd = open("out.log", "w+");
|
|
|
|
|
int errfd = open("err.log", "w+");
|
|
|
|
|
virCommandSetOutputFD(cmd, &outfd);
|
|
|
|
|
virCommandSetErrorFD(cmd, &errfd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Alternatively it is possible to request that a pipe be
|
|
|
|
|
created to fetch stdout/err in the parent, by initializing
|
|
|
|
|
the FD to -1.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
int outfd = -1;
|
|
|
|
|
int errfd = -1
|
|
|
|
|
virCommandSetOutputFD(cmd, &outfd);
|
|
|
|
|
virCommandSetErrorFD(cmd, &errfd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Once the command is running, <code>outfd</code>
|
|
|
|
|
and <code>errfd</code> will be initialized with
|
|
|
|
|
valid file handles that can be read from. It is
|
|
|
|
|
permissible to pass the same pointer for both outfd
|
|
|
|
|
and errfd, in which case both standard streams in
|
|
|
|
|
the child will share the same fd in the parent.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Normally, file descriptors opened to collect output from a child
|
|
|
|
|
process perform blocking I/O, but the parent process can request
|
|
|
|
|
non-blocking mode:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandNonblockingFDs(cmd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="buffers">Feeding & capturing strings to/from the child</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
2010-12-06 23:36:34 +00:00
|
|
|
Often dealing with file handles for stdin/out/err is
|
|
|
|
|
unnecessarily complex; an alternative is to let virCommandRun
|
|
|
|
|
perform the I/O and interact via string buffers. Use of a buffer
|
|
|
|
|
only works with virCommandRun, and cannot be mixed with pipe
|
|
|
|
|
file descriptors. That is, the choice is generally between
|
|
|
|
|
managing all I/O in the caller (any fds not specified are tied
|
|
|
|
|
to /dev/null), or letting virCommandRun manage all I/O via
|
|
|
|
|
strings (unspecified stdin is tied to /dev/null, and unspecified
|
|
|
|
|
output streams get logged but are otherwise discarded).
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
It is possible to specify a string buffer to act as the data
|
|
|
|
|
source for the child's stdin, if there are no embedded NUL
|
|
|
|
|
bytes, and if the command will be run with virCommandRun:
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
const char *input = "Hello World\n";
|
|
|
|
|
virCommandSetInputBuffer(cmd, input);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Similarly it is possible to request that the child's
|
|
|
|
|
stdout/err be redirected into a string buffer, if the
|
|
|
|
|
output is not expected to contain NUL bytes, and if
|
|
|
|
|
the command will be run with virCommandRun:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
char *output = NULL, *errors = NULL;
|
|
|
|
|
virCommandSetOutputBuffer(cmd, &output);
|
|
|
|
|
virCommandSetErrorBuffer(cmd, &errors);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
2010-12-03 21:14:16 +00:00
|
|
|
Once the command has finished executing, these buffers will
|
|
|
|
|
contain the output. Allocation is guaranteed if virCommandRun
|
|
|
|
|
or virCommandWait succeed (if there was no output, then the
|
|
|
|
|
buffer will contain an allocated empty string); if the command
|
|
|
|
|
failed, then the buffers usually contain a best-effort
|
|
|
|
|
allocation of collected information (however, on an
|
|
|
|
|
out-of-memory condition, the buffer may still be NULL). The
|
|
|
|
|
caller is responsible for freeing registered buffers, since the
|
2012-01-27 22:40:20 +00:00
|
|
|
buffers are designed to persist beyond virCommandFree. It
|
|
|
|
|
is possible to pass the same pointer to both
|
|
|
|
|
virCommandSetOutputBuffer and virCommandSetErrorBuffer, in which
|
|
|
|
|
case the child process interleaves output into a single string.
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h3><a name="directory">Setting working directory</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Daemonized commands are always run with "/" as the current
|
|
|
|
|
working directory. All other commands default to running in the
|
|
|
|
|
same working directory as the parent process, but an alternate
|
|
|
|
|
directory can be specified:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandSetWorkingDirectory(cmd, LOCALSTATEDIR);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="hooks">Any additional hooks</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
If anything else is needed, it is possible to request a hook
|
|
|
|
|
function that is called in the child after the fork, as the
|
|
|
|
|
last thing before changing directories, dropping capabilities,
|
|
|
|
|
and executing the new process. If hook(opaque) returns
|
|
|
|
|
non-zero, then the child process will not be run.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandSetPreExecHook(cmd, hook, opaque);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="logging">Logging commands</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Sometimes, it is desirable to log what command will be run, or
|
|
|
|
|
even to use virCommand solely for creation of a single
|
|
|
|
|
consolidated string without running anything.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
int logfd = ...;
|
|
|
|
|
char *timestamp = virTimestamp();
|
|
|
|
|
char *string = NULL;
|
|
|
|
|
|
|
|
|
|
dprintf(logfd, "%s: ", timestamp);
|
|
|
|
|
VIR_FREE(timestamp);
|
|
|
|
|
virCommandWriteArgLog(cmd, logfd);
|
|
|
|
|
|
|
|
|
|
string = virCommandToString(cmd);
|
|
|
|
|
if (string)
|
|
|
|
|
VIR_DEBUG("about to run %s", string);
|
|
|
|
|
VIR_FREE(string);
|
|
|
|
|
if (virCommandRun(cmd, NULL) < 0)
|
|
|
|
|
return -1;
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="sync">Running commands synchronously</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
For most commands, the desired behaviour is to spawn
|
|
|
|
|
the command, wait for it to complete & exit and then
|
|
|
|
|
check that its exit status is zero
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
if (virCommandRun(cmd, NULL) < 0)
|
|
|
|
|
return -1;
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
<strong>Note:</strong> if the command has been daemonized
|
|
|
|
|
this will only block & wait for the intermediate process,
|
|
|
|
|
not the real command. <code>virCommandRun</code> will
|
2011-10-10 20:02:06 +00:00
|
|
|
report on any errors that have occurred upon this point
|
2010-05-25 13:14:46 +00:00
|
|
|
with all previous API calls. If the command fails to
|
|
|
|
|
run, or exits with non-zero status an error will be
|
|
|
|
|
reported via normal libvirt error infrastructure. If a
|
|
|
|
|
non-zero exit status can represent a success condition,
|
|
|
|
|
it is possible to request the exit status and perform
|
|
|
|
|
that check manually instead of letting <code>virCommandRun</code>
|
2014-02-20 00:32:19 +00:00
|
|
|
raise the error. By default, the captured status is only
|
|
|
|
|
for a normal exit (death from a signal is treated as an error),
|
|
|
|
|
but a caller can use <code>virCommandRawStatus</code> to get
|
|
|
|
|
encoded status that includes any terminating signals.
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
int status;
|
|
|
|
|
if (virCommandRun(cmd, &status) < 0)
|
|
|
|
|
return -1;
|
|
|
|
|
if (status == 1) {
|
|
|
|
|
...do stuff...
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
virCommandRawStatus(cmd2);
|
|
|
|
|
if (virCommandRun(cmd2, &status) < 0)
|
|
|
|
|
return -1;
|
|
|
|
|
if (WIFEXITED(status) && WEXITSTATUS(status) == 1) {
|
|
|
|
|
...do stuff...
|
|
|
|
|
}
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h3><a name="async">Running commands asynchronously</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In certain complex scenarios, particularly special
|
|
|
|
|
I/O handling is required for the child's stdin/err/out
|
|
|
|
|
it will be necessary to run the command asynchronously
|
|
|
|
|
and wait for completion separately.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
pid_t pid;
|
|
|
|
|
if (virCommandRunAsync(cmd, &pid) < 0)
|
|
|
|
|
return -1;
|
2010-05-25 13:14:46 +00:00
|
|
|
|
2016-11-11 22:40:27 +00:00
|
|
|
... do something while pid is running ...
|
2010-05-25 13:14:46 +00:00
|
|
|
|
2016-11-11 22:40:27 +00:00
|
|
|
int status;
|
|
|
|
|
if (virCommandWait(cmd, &status) < 0)
|
|
|
|
|
return -1;
|
2010-05-25 13:14:46 +00:00
|
|
|
|
2016-11-11 22:40:27 +00:00
|
|
|
if (WEXITSTATUS(status)...) {
|
|
|
|
|
..do stuff..
|
|
|
|
|
}
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
As with <code>virCommandRun</code>, the <code>status</code>
|
|
|
|
|
arg for <code>virCommandWait</code> can be omitted, in which
|
|
|
|
|
case it will validate that exit status is zero and raise an
|
|
|
|
|
error if not.
|
|
|
|
|
</p>
|
|
|
|
|
|
2011-07-12 16:42:41 +00:00
|
|
|
<p>
|
|
|
|
|
There are two approaches to child process cleanup, determined by
|
|
|
|
|
how long you want to keep the virCommand object in scope.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>1. If the virCommand object will outlast the child process,
|
|
|
|
|
then pass NULL for the pid argument, and the child process will
|
|
|
|
|
automatically be reaped at virCommandFree, unless you reap it
|
|
|
|
|
sooner via virCommandWait or virCommandAbort.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<p>2. If the child process must exist on at least one code path
|
|
|
|
|
after virCommandFree, then pass a pointer for the pid argument.
|
|
|
|
|
Later, to clean up the child, call virPidWait or virPidAbort.
|
|
|
|
|
Before virCommandFree, you can still use virCommandWait or
|
|
|
|
|
virCommandAbort to reap the process.
|
|
|
|
|
</p>
|
2010-05-25 13:14:46 +00:00
|
|
|
|
|
|
|
|
<h3><a name="release">Releasing resources</a></h3>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
Once the command has been executed, or if execution
|
|
|
|
|
has been abandoned, it is necessary to release
|
|
|
|
|
resources associated with the <code>virCommandPtr</code>
|
|
|
|
|
object. This is done with:
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
2016-11-11 22:40:27 +00:00
|
|
|
virCommandFree(cmd);
|
2010-05-25 13:14:46 +00:00
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
There is no need to check if <code>cmd</code> is NULL
|
|
|
|
|
before calling <code>virCommandFree</code>. This scenario
|
|
|
|
|
is handled automatically. If the command is still running,
|
2014-03-27 05:49:48 +00:00
|
|
|
it will be forcibly killed and cleaned up (via waitpid).
|
2010-05-25 13:14:46 +00:00
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<h2><a name="example">Complete examples</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
This shows a complete example usage of the APIs roughly
|
|
|
|
|
using the libvirt source src/util/hooks.c
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
int runhook(const char *drvstr, const char *id,
|
|
|
|
|
const char *opstr, const char *subopstr,
|
2014-03-18 08:19:33 +00:00
|
|
|
const char *extra)
|
|
|
|
|
{
|
2010-05-25 13:14:46 +00:00
|
|
|
int ret;
|
|
|
|
|
char *path;
|
|
|
|
|
virCommandPtr cmd;
|
|
|
|
|
|
|
|
|
|
ret = virBuildPath(&path, LIBVIRT_HOOK_DIR, drvstr);
|
|
|
|
|
if ((ret < 0) || (path == NULL)) {
|
|
|
|
|
virHookReportError(VIR_ERR_INTERNAL_ERROR,
|
|
|
|
|
_("Failed to build path for %s hook"),
|
|
|
|
|
drvstr);
|
|
|
|
|
return -1;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
cmd = virCommandNew(path);
|
|
|
|
|
VIR_FREE(path);
|
|
|
|
|
|
|
|
|
|
virCommandAddEnvPassCommon(cmd);
|
|
|
|
|
|
|
|
|
|
virCommandAddArgList(cmd, id, opstr, subopstr, extra, NULL);
|
|
|
|
|
|
|
|
|
|
virCommandSetInputBuffer(cmd, input);
|
|
|
|
|
|
|
|
|
|
ret = virCommandRun(cmd, NULL);
|
|
|
|
|
|
|
|
|
|
virCommandFree(cmd);
|
|
|
|
|
|
|
|
|
|
return ret;
|
|
|
|
|
}
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
In this example, the command is being run synchronously.
|
|
|
|
|
A pre-formatted string is being fed to the command as
|
|
|
|
|
its stdin. The command takes four arguments, and has a
|
|
|
|
|
minimal set of environment variables passed down. In
|
|
|
|
|
this example, the code does not require any error checking.
|
|
|
|
|
All errors are reported by the <code>virCommandRun</code>
|
|
|
|
|
method, and the exit status from this is returned to
|
|
|
|
|
the caller to handle as desired.
|
|
|
|
|
</p>
|
|
|
|
|
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
