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libxl: acquire a pidfile in the driver root directory

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When we allow multiple instances of the driver for the same user
account, using a separate root directory, we need to ensure mutual
exclusion. Use a pidfile to guarantee this.

In privileged libvirtd this ends up locking

   /var/run/libvirt/libxl/driver.pid

In unprivileged libvirtd this ends up locking

  /run/user/$UID/libvirt/libxl/run/driver.pid

NB, the latter can vary depending on $XDG_RUNTIME_DIR

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2019-05-23 11:34:08 +01:00
parent defddd0476
commit 59080d84c0
2 changed files with 13 additions and 1 deletions
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3
src/libxl/libxl_conf.h
View File

@ -111,6 +111,9 @@ struct _libxlDriverPrivate {
* then lockless thereafter */
libxlDriverConfigPtr config;
/* pid file FD, ensures two copies of the driver can't use the same root */
int lockFD;
/* Atomic inc/dec only */
unsigned int nactive;

11
src/libxl/libxl_driver.c
View File

@ -53,6 +53,7 @@
#include "viraccessapicheck.h"
#include "viratomic.h"
#include "virhostdev.h"
#include "virpidfile.h"
#include "locking/domain_lock.h"
#include "virnetdevtap.h"
#include "cpu/cpu.h"
@ -506,7 +507,6 @@ libxlStateCleanup(void)
return -1;
virObjectUnref(libxl_driver->hostdevMgr);
virObjectUnref(libxl_driver->config);
virObjectUnref(libxl_driver->xmlopt);
virObjectUnref(libxl_driver->domains);
virPortAllocatorRangeFree(libxl_driver->reservedGraphicsPorts);
@ -516,6 +516,10 @@ libxlStateCleanup(void)
virObjectUnref(libxl_driver->domainEventState);
virSysinfoDefFree(libxl_driver->hostsysinfo);
if (libxl_driver->lockFD != -1)
virPidFileRelease(libxl_driver->config->stateDir, "driver", libxl_driver->lockFD);
virObjectUnref(libxl_driver->config);
virMutexDestroy(&libxl_driver->lock);
VIR_FREE(libxl_driver);
@ -658,6 +662,7 @@ libxlStateInitialize(bool privileged,
if (VIR_ALLOC(libxl_driver) < 0)
return -1;
libxl_driver->lockFD = -1;
if (virMutexInit(&libxl_driver->lock) < 0) {
virReportError(VIR_ERR_INTERNAL_ERROR,
"%s", _("cannot initialize mutex"));
@ -741,6 +746,10 @@ libxlStateInitialize(bool privileged,
goto error;
}
if ((libxl_driver->lockFD =
virPidFileAcquire(cfg->stateDir, "driver", true, getpid())) < 0)
goto error;
if (!(libxl_driver->lockManager =
virLockManagerPluginNew(cfg->lockManagerName ?
cfg->lockManagerName : "nop",