libvirt/src/util/virnetdevveth.c
Michal Privoznik c0d162c68c virNetDevVethCreate: Serialize callers
Consider dozen of LXC domains, each of them having this type of interface:

    <interface type='network'>
      <mac address='52:54:00:a7:05:4b'/>
      <source network='default'/>
    </interface>

When starting these domain in parallel, all workers may meet in
virNetDevVethCreate() where a race starts. Race over allocating veth
pairs because allocation requires two steps:

  1) find first nonexistent '/sys/class/net/vnet%d/'
  2) run 'ip link add ...' command

Now consider two threads. Both of them find N as the first unused veth
index but only one of them succeeds allocating it. The other one fails.
For such cases, we are running the allocation in a loop with 10 rounds.
However this is very flaky synchronization. It should be rather used
when libvirt is competing with other process than when libvirt threads
fight each other. Therefore, internally we should use mutex to serialize
callers, and do the allocation in loop (just in case we are competing
with a different process). By the way we have something similar already
since 1cf97c87.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
2014-02-26 08:50:47 +01:00

242 lines
6.9 KiB
C

/*
* Copyright (C) 2010-2013 Red Hat, Inc.
* Copyright IBM Corp. 2008
*
* 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/>.
*
* Authors:
* David L. Leskovec <dlesko at linux.vnet.ibm.com>
* Daniel P. Berrange <berrange@redhat.com>
*/
#include <config.h>
#include <sys/wait.h>
#include "virnetdevveth.h"
#include "viralloc.h"
#include "virlog.h"
#include "vircommand.h"
#include "virerror.h"
#include "virfile.h"
#include "virstring.h"
#include "virutil.h"
#include "virnetdev.h"
#define VIR_FROM_THIS VIR_FROM_NONE
/* Functions */
virMutex virNetDevVethCreateMutex;
static int virNetDevVethCreateMutexOnceInit(void)
{
if (virMutexInit(&virNetDevVethCreateMutex) < 0) {
virReportSystemError(errno, "%s", _("unable to init mutex"));
return -1;
}
return 0;
}
VIR_ONCE_GLOBAL_INIT(virNetDevVethCreateMutex);
static int virNetDevVethExists(int devNum)
{
int ret;
char *path = NULL;
if (virAsprintf(&path, "/sys/class/net/vnet%d/", devNum) < 0)
return -1;
ret = virFileExists(path) ? 1 : 0;
VIR_DEBUG("Checked dev vnet%d usage: %d", devNum, ret);
VIR_FREE(path);
return ret;
}
/**
* virNetDevVethGetFreeNum:
* @startDev: device number to start at (x in vethx)
*
* Looks in /sys/class/net/ to find the first available veth device
* name.
*
* Returns non-negative device number on success or -1 in case of error
*/
static int virNetDevVethGetFreeNum(int startDev)
{
int devNum;
#define MAX_DEV_NUM 65536
for (devNum = startDev; devNum < MAX_DEV_NUM; devNum++) {
int ret = virNetDevVethExists(devNum);
if (ret < 0)
return -1;
if (ret == 0)
return devNum;
}
virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("No free veth devices available"));
return -1;
}
/**
* virNetDevVethCreate:
* @veth1: pointer to name for parent end of veth pair
* @veth2: pointer to return name for container end of veth pair
*
* Creates a veth device pair using the ip command:
* ip link add veth1 type veth peer name veth2
* If veth1 points to NULL on entry, it will be a valid interface on
* return. veth2 should point to NULL on entry.
*
* NOTE: If veth1 and veth2 names are not specified, ip will auto assign
* names. There seems to be two problems here -
* 1) There doesn't seem to be a way to determine the names of the
* devices that it creates. They show up in ip link show and
* under /sys/class/net/ however there is no guarantee that they
* are the devices that this process just created.
* 2) Once one of the veth devices is moved to another namespace, it
* is no longer visible in the parent namespace. This seems to
* confuse the name assignment causing it to fail with File exists.
* Because of these issues, this function currently allocates names
* prior to using the ip command, and returns any allocated names
* to the caller.
*
* Returns 0 on success or -1 in case of error
*/
int virNetDevVethCreate(char** veth1, char** veth2)
{
int ret = -1;
char *veth1auto = NULL;
char *veth2auto = NULL;
int vethNum = 0;
virCommandPtr cmd = NULL;
size_t i;
/*
* We might race with other containers, but this is reasonably
* unlikely, so don't do too many retries for device creation
*/
if (virNetDevVethCreateMutexInitialize() < 0)
return -1;
virMutexLock(&virNetDevVethCreateMutex);
#define MAX_VETH_RETRIES 10
for (i = 0; i < MAX_VETH_RETRIES; i++) {
int status;
if (!*veth1) {
int veth1num;
if ((veth1num = virNetDevVethGetFreeNum(vethNum)) < 0)
goto cleanup;
if (virAsprintf(&veth1auto, "vnet%d", veth1num) < 0)
goto cleanup;
vethNum = veth1num + 1;
}
if (!*veth2) {
int veth2num;
if ((veth2num = virNetDevVethGetFreeNum(vethNum)) < 0)
goto cleanup;
if (virAsprintf(&veth2auto, "vnet%d", veth2num) < 0)
goto cleanup;
vethNum = veth2num + 1;
}
cmd = virCommandNew("ip");
virCommandAddArgList(cmd, "link", "add",
*veth1 ? *veth1 : veth1auto,
"type", "veth", "peer", "name",
*veth2 ? *veth2 : veth2auto,
NULL);
if (virCommandRun(cmd, &status) < 0)
goto cleanup;
if (status == 0) {
if (veth1auto) {
*veth1 = veth1auto;
veth1auto = NULL;
}
if (veth2auto) {
*veth2 = veth2auto;
veth2auto = NULL;
}
VIR_DEBUG("Create Host: %s guest: %s", *veth1, *veth2);
ret = 0;
goto cleanup;
}
VIR_DEBUG("Failed to create veth host: %s guest: %s: %d",
*veth1 ? *veth1 : veth1auto,
*veth1 ? *veth1 : veth1auto,
status);
VIR_FREE(veth1auto);
VIR_FREE(veth2auto);
virCommandFree(cmd);
cmd = NULL;
}
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Failed to allocate free veth pair after %d attempts"),
MAX_VETH_RETRIES);
cleanup:
virMutexUnlock(&virNetDevVethCreateMutex);
virCommandFree(cmd);
VIR_FREE(veth1auto);
VIR_FREE(veth2auto);
return ret;
}
/**
* virNetDevVethDelete:
* @veth: name for one end of veth pair
*
* This will delete both veth devices in a pair. Only one end needs to
* be specified. The ip command will identify and delete the other veth
* device as well.
* ip link del veth
*
* Returns 0 on success or -1 in case of error
*/
int virNetDevVethDelete(const char *veth)
{
virCommandPtr cmd = virCommandNewArgList("ip", "link", "del", veth, NULL);
int status;
int ret = -1;
if (virCommandRun(cmd, &status) < 0)
goto cleanup;
if (status != 0) {
if (!virNetDevExists(veth)) {
VIR_DEBUG("Device %s already deleted (by kernel namespace cleanup)", veth);
ret = 0;
goto cleanup;
}
virReportError(VIR_ERR_INTERNAL_ERROR,
_("Failed to delete veth device %s"), veth);
goto cleanup;
}
ret = 0;
cleanup:
virCommandFree(cmd);
return ret;
}