[PATCH 4/8] qemu: add a DBus daemon helper unit
Michal Privoznik
mprivozn at redhat.com
Thu Feb 20 09:04:19 UTC 2020
On 1/14/20 2:46 PM, marcandre.lureau at redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau at redhat.com>
>
> Add a unit to start & stop a private dbus-daemon.
>
> The daemon is meant to be started on demand, and associated with a
> QEMU process. It should be stopped when the QEMU process is stopped.
>
> The current policy is permissive like a session bus. Stricter
> policies can be added later, following recommendations from:
> https://git.qemu.org/?p=qemu.git;a=blob;f=docs/interop/dbus.rst
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau at redhat.com>
> ---
> src/qemu/Makefile.inc.am | 4 +
> src/qemu/qemu_dbus.c | 299 +++++++++++++++++++++++++++++++++++++++
> src/qemu/qemu_dbus.h | 40 ++++++
> src/qemu/qemu_domain.c | 2 +
> src/qemu/qemu_domain.h | 3 +
> tests/Makefile.am | 1 +
> 6 files changed, 349 insertions(+)
> create mode 100644 src/qemu/qemu_dbus.c
> create mode 100644 src/qemu/qemu_dbus.h
>
> diff --git a/src/qemu/Makefile.inc.am b/src/qemu/Makefile.inc.am
> index 028ab9043c..833638ec3c 100644
> --- a/src/qemu/Makefile.inc.am
> +++ b/src/qemu/Makefile.inc.am
> @@ -69,6 +69,8 @@ QEMU_DRIVER_SOURCES = \
> qemu/qemu_checkpoint.h \
> qemu/qemu_backup.c \
> qemu/qemu_backup.h \
> + qemu/qemu_dbus.c \
> + qemu/qemu_dbus.h \
These can be added where they were just a moment ago ;-)
> $(NULL)
>
>
> @@ -93,6 +95,7 @@ libvirt_driver_qemu_impl_la_CFLAGS = \
> $(LIBNL_CFLAGS) \
> $(SELINUX_CFLAGS) \
> $(XDR_CFLAGS) \
> + $(DBUS_CFLAGS) \
> -I$(srcdir)/access \
> -I$(builddir)/access \
> -I$(srcdir)/conf \
> @@ -105,6 +108,7 @@ libvirt_driver_qemu_impl_la_LIBADD = \
> $(GNUTLS_LIBS) \
> $(LIBNL_LIBS) \
> $(SELINUX_LIBS) \
> + $(DBUS_LIBS) \
> $(LIBXML_LIBS) \
> $(NULL)
> libvirt_driver_qemu_impl_la_SOURCES = $(QEMU_DRIVER_SOURCES)
> diff --git a/src/qemu/qemu_dbus.c b/src/qemu/qemu_dbus.c
> new file mode 100644
> index 0000000000..9c8a03c947
> --- /dev/null
> +++ b/src/qemu/qemu_dbus.c
> @@ -0,0 +1,299 @@
> +/*
> + * qemu_dbus.c: QEMU dbus daemon
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library 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
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library. If not, see
> + * <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <config.h>
> +
> +#include "qemu_extdevice.h"
> +#include "qemu_dbus.h"
> +#include "qemu_security.h"
> +
> +#include "viralloc.h"
> +#include "virlog.h"
> +#include "virstring.h"
> +#include "virtime.h"
> +#include "virpidfile.h"
> +
> +#define VIR_FROM_THIS VIR_FROM_NONE
> +
> +VIR_LOG_INIT("qemu.dbus");
> +
> +
> +int
> +qemuDBusPrepareHost(virQEMUDriverPtr driver)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> +
> + return virDirCreate(cfg->dbusStateDir, 0770, cfg->user, cfg->group,
> + VIR_DIR_CREATE_ALLOW_EXIST);
> +}
> +
> +
> +static char *
> +qemuDBusCreatePidFilename(const char *stateDir,
> + const char *shortName)
> +{
> + g_autofree char *name = g_strdup_printf("%s-dbus", shortName);
> +
> + return virPidFileBuildPath(stateDir, name);
Instead of having each caller pass cfg->dbusStateDir, we can accept cfg
here and deref ourselves.
> +}
> +
> +
> +static char *
> +qemuDBusCreateFilename(const char *stateDir,
> + const char *shortName,
> + const char *ext)
> +{
> + g_autofree char *name = g_strdup_printf("%s-dbus", shortName);
> +
> + return virFileBuildPath(stateDir, name, ext);
> +}
> +
> +
> +static char *
> +qemuDBusCreateSocketPath(virQEMUDriverConfigPtr cfg,
> + const char *shortName)
> +{
> + return qemuDBusCreateFilename(cfg->dbusStateDir, shortName, ".sock");
> +}
> +
I'd introduce qemuDBusCreateConfPath() so that nobody else has to call
qemuDBusCreateFilename() again.
> +
> +char *
> +qemuDBusGetAddress(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + g_autofree char *shortName = virDomainDefGetShortName(vm->def);
> + g_autofree char *path = qemuDBusCreateSocketPath(cfg, shortName);
> +
> + return g_strdup_printf("unix:path=%s", path);
> +}
> +
> +
> +static int
> +qemuDBusGetPid(const char *binPath,
> + const char *stateDir,
> + const char *shortName,
> + pid_t *pid)
> +{
> + g_autofree char *pidfile = qemuDBusCreatePidFilename(stateDir, shortName);
> +
> + return virPidFileReadPathIfAlive(pidfile, pid, binPath);
> +}
After the daemon startup is reworked, this function is no longer needed.
> +
> +
> +static int
> +qemuDBusWriteConfig(const char *filename, const char *path)
> +{
> + virBuffer buf = VIR_BUFFER_INITIALIZER;
> + g_autofree char *config = NULL;
> +
> + virBufferAddLit(&buf, "<!DOCTYPE busconfig PUBLIC \"-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN\"\n");
> + virBufferAddLit(&buf, " \"http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd\">\n");
> + virBufferAddLit(&buf, "<busconfig>\n");
> + virBufferAdjustIndent(&buf, 2);
> +
> + virBufferAddLit(&buf, "<type>org.libvirt.qemu</type>\n");
> + virBufferAsprintf(&buf, "<listen>unix:path=%s</listen>\n", path);
> + virBufferAddLit(&buf, "<auth>EXTERNAL</auth>\n");
> +
> + virBufferAddLit(&buf, "<policy context='default'>\n");
> + virBufferAddLit(&buf, " <!-- Allow everything to be sent -->\n");
> + virBufferAddLit(&buf, " <allow send_destination='*' eavesdrop='true'/>\n");
> + virBufferAddLit(&buf, " <!-- Allow everything to be received -->\n");
> + virBufferAddLit(&buf, " <allow eavesdrop='true'/>\n");
> + virBufferAddLit(&buf, " <!-- Allow anyone to own anything -->\n");
> + virBufferAddLit(&buf, " <allow own='*'/>\n");
'make syntax-check' complains about these leading spaces. Pff.
> + virBufferAddLit(&buf, "</policy>\n");
> +
> + virBufferAddLit(&buf, "<include if_selinux_enabled='yes' selinux_root_relative='yes'>contexts/dbus_contexts</include>\n");
> +
> + virBufferAdjustIndent(&buf, -2);
> + virBufferAddLit(&buf, "</busconfig>\n");
> +
> + config = virBufferContentAndReset(&buf);
> +
> + return virFileWriteStr(filename, config, 0600);
> +}
> +
> +
> +void
> +qemuDBusStop(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + g_autofree char *shortName = NULL;
> + g_autofree char *pidfile = NULL;
> + g_autofree char *configfile = NULL;
> + virErrorPtr orig_err;
> + int rc;
> + pid_t pid;
> +
> + shortName = virDomainDefGetShortName(vm->def);
> + pidfile = qemuDBusCreatePidFilename(cfg->dbusStateDir, shortName);
> + configfile = qemuDBusCreateFilename(cfg->dbusStateDir, shortName, ".conf");
> +
> + rc = qemuDBusGetPid(cfg->dbusDaemonName, cfg->dbusStateDir, shortName, &pid);
> + if (rc == 0 && pid != (pid_t)-1) {
> + char ebuf[1024];
> +
> + VIR_DEBUG("Killing dbus-daemon process %lld", (long long)pid);
> + if (virProcessKill(pid, SIGTERM) < 0 && errno != ESRCH)
> + VIR_ERROR(_("Failed to kill process %lld: %s"),
> + (long long)pid,
> + virStrerror(errno, ebuf, sizeof(ebuf)));
> + }
> +
No need to specifically kill the process. virPidFileForceCleanupPath()
does that.
> + virErrorPreserveLast(&orig_err);
> + if (virPidFileForceCleanupPath(pidfile) < 0) {
> + VIR_WARN("Unable to kill dbus-daemon process");
> + } else {
> + if (unlink(pidfile) < 0 &&
> + errno != ENOENT) {
> + virReportSystemError(errno,
> + _("Unable to remove stale pidfile %s"),
> + pidfile);
> + }
Just like it unlinks the pidfile.
> + }
> + if (unlink(configfile) < 0 &&
> + errno != ENOENT) {
> + virReportSystemError(errno,
> + _("Unable to remove stale configfile %s"),
> + pidfile);
> + }
> + virErrorRestore(&orig_err);
> +
> + priv->dbusDaemonRunning = false;
We can do this only in success path.
> +}
> +
> +
> +int
> +qemuDBusStart(virQEMUDriverPtr driver,
> + virDomainObjPtr vm)
> +{
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + g_autoptr(virCommand) cmd = NULL;
> + g_autofree char *shortName = NULL;
> + g_autofree char *pidfile = NULL;
> + g_autofree char *configfile = NULL;
> + g_autofree char *sockpath = NULL;
> + virTimeBackOffVar timebackoff;
> + const unsigned long long timeout = 500 * 1000; /* ms */
> + int errfd = -1;
s/int/VIR_AUTOCLOSE/ to make sure the FD is closed when returning from
the function.
> + int cmdret = 0;
> + int exitstatus = 0;
> +
> + if (priv->dbusDaemonRunning)
> + return 0;
> +
> + /* for cleanup */
> + qemuDBusStop(driver, vm);
> +
> + cmd = virCommandNew(cfg->dbusDaemonName);
> + shortName = virDomainDefGetShortName(vm->def);
This can fail and this the retval needs to be checked for.
> + pidfile = qemuDBusCreatePidFilename(cfg->dbusStateDir, shortName);
> + configfile = qemuDBusCreateFilename(cfg->dbusStateDir, shortName, ".conf");
> + sockpath = qemuDBusCreateSocketPath(cfg, shortName);
> +
> + if (qemuDBusWriteConfig(configfile, sockpath) < 0) {
> + virReportSystemError(errno, _("Failed to write '%s'"), configfile);
> + return -1;
> + }
> +
> + if (qemuSecurityDomainSetPathLabel(driver, vm, configfile, false) < 0)
> + return -1;
> +
> + virCommandClearCaps(cmd);
> + virCommandSetPidFile(cmd, pidfile);
> + virCommandSetErrorFD(cmd, &errfd);
> + virCommandDaemonize(cmd);
> + virCommandAddArgFormat(cmd, "--config-file=%s", configfile);
> +
> + if (qemuExtDeviceLogCommand(driver, vm, cmd, "DBus") < 0)
> + return -1;
> +
> + if (qemuSecurityCommandRun(driver, vm, cmd, -1, -1,
> + &exitstatus, &cmdret) < 0)
> + return -1;
> +
> + if (cmdret < 0 || exitstatus != 0) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("Could not start dbus-daemon. exitstatus: %d"), exitstatus);
> + return -1;
> + }
> +
> + if (virTimeBackOffStart(&timebackoff, 1, timeout) < 0)
> + return -1;
> + while (virTimeBackOffWait(&timebackoff)) {
> + pid_t pid;
> +
> + if (qemuDBusGetPid(cfg->dbusDaemonName, cfg->dbusStateDir, shortName, &pid) < 0)
> + continue;
> +
There is no need to read the pid in every iteration. The virCommandRun()
(wrapped in qemuSecurityCommandRun()) will write the pidfile right
before exec(). So I think this loop should look a bit different:
while (virTimeBackOffWait(&timebackoff)) {
if (virFileExists(sockpath))
break;
if (pid still exists)
continue;
read the error;
goto cleanup;
}
Oh, and we will need cleanup label, so that in case of failure happening
after we've forked off a child, we make sure to kill it.
> + if (pid == (pid_t)-1)
> + break;
> +
> + if (virFileExists(sockpath))
> + break;
> + }
> +
> + if (!virFileExists(sockpath)) {
> + char errbuf[1024] = { 0 };
> +
> + if (saferead(errfd, errbuf, sizeof(errbuf) - 1) < 0) {
> + virReportSystemError(errno, "%s", _("dbus-daemon died unexpectedly"));
> + } else {
> + virReportError(VIR_ERR_OPERATION_FAILED,
> + _("dbus-daemon died and reported: %s"), errbuf);
> + }
> +
> + return -1;
> + }
This looks like a perfect place to put the children process into CGroup.
You define a function for that below but never call it ;-)
> +
> + if (qemuSecurityDomainSetPathLabel(driver, vm, sockpath, false) < 0)
> + return -1;
> +
> + priv->dbusDaemonRunning = true;
> +
> + return 0;
> +}
> +
> +
> +int
> +qemuDBusSetupCgroup(virQEMUDriverPtr driver,
> + virDomainDefPtr def,
> + virCgroupPtr cgroup)
> +{
> + virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> + g_autofree char *shortName = virDomainDefGetShortName(def);
> + pid_t pid;
> + int rc;
> +
> + rc = qemuDBusGetPid(cfg->dbusDaemonName, cfg->dbusStateDir, shortName, &pid);
> + if (rc < 0 || (rc == 0 && pid == (pid_t)-1)) {
> + virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> + _("Could not get process id of dbus-daemon"));
> + return -1;
> + }
> +
> + if (virCgroupAddProcess(cgroup, pid) < 0)
> + return -1;
> +
> + return 0;
> +}
> diff --git a/src/qemu/qemu_dbus.h b/src/qemu/qemu_dbus.h
> new file mode 100644
> index 0000000000..8728824bd7
> --- /dev/null
> +++ b/src/qemu/qemu_dbus.h
> @@ -0,0 +1,40 @@
> +/*
> + * qemu_dbus.h: QEMU dbus daemon
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library 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
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library. If not, see
> + * <http://www.gnu.org/licenses/>.
> + */
> +
> +#pragma once
> +
> +#include "qemu_conf.h"
> +#include "qemu_domain.h"
> +
> +int qemuDBusPrepareHost(virQEMUDriverPtr driver);
> +
> +char *qemuDBusGetAddress(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +int qemuDBusConnect(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +int qemuDBusStart(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +void qemuDBusStop(virQEMUDriverPtr driver,
> + virDomainObjPtr vm);
> +
> +int qemuDBusSetupCgroup(virQEMUDriverPtr driver,
> + virDomainDefPtr def,
> + virCgroupPtr cgroup);
Interesting, qemuDBusConnect() is declared but never defined and my gcc
doesn't complain (!).
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index ecd087a5cb..7722a53c62 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -2264,6 +2264,8 @@ qemuDomainObjPrivateDataClear(qemuDomainObjPrivatePtr priv)
>
> /* reset node name allocator */
> qemuDomainStorageIdReset(priv);
> +
> + priv->dbusDaemonRunning = false;
> }
>
This shouldn't be necessary. If the qemuDBusStop() is called
>
> diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
> index b2041ccea7..02c792ea2a 100644
> --- a/src/qemu/qemu_domain.h
> +++ b/src/qemu/qemu_domain.h
> @@ -40,6 +40,7 @@
> #include "logging/log_manager.h"
> #include "virdomainmomentobjlist.h"
> #include "virenum.h"
> +#include "virdbus.h"
>
I don't think this is needed - you are not introducing anything DBus
related in qemu_domain.h. If this is dropped then the Makefile.am change
done below can be dropped too.
> #define QEMU_DOMAIN_FORMAT_LIVE_FLAGS \
> (VIR_DOMAIN_XML_SECURE)
> @@ -417,6 +418,8 @@ struct _qemuDomainObjPrivate {
>
> /* running backup job */
> virDomainBackupDefPtr backup;
> +
> + bool dbusDaemonRunning;
> };
>
> #define QEMU_DOMAIN_PRIVATE(vm) \
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index f957c7d1ba..8ed5afbb9b 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -45,6 +45,7 @@ AM_CFLAGS = \
> $(YAJL_CFLAGS) \
> $(COVERAGE_CFLAGS) \
> $(XDR_CFLAGS) \
> + $(DBUS_CFLAGS) \
> $(WARN_CFLAGS)
>
> AM_LDFLAGS = \
>
Michal
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