Re: [Xen-devel] [libvirt] [PATCH v2] libxl: free ifname on libxlDomainMigrationPrepareDef

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 12/06/2015 10:59 AM, Jim Fehlig wrote:
> On 12/06/2015 10:04 AM, Jim Fehlig wrote:
>> On 12/04/2015 12:45 PM, Joao Martins wrote:
>>> Commit d2e5538b1 changes virDomainDef to include ifnames
>>> that autogenerated by libxl, and that are also cleared
>>> on domain cleanup. One place that's missing is on
>>> migration, when domain xml is sent to dst libvirtd and
>>> would contain ifnames from the source libvirtd. This
>>> would lead to erronous behaviour (as seen in osstest CI)
>>> such as failing to migrate when a vif with the same name
>>> existed (belonging to another domain) on destination.
>> Your patch is certainly one way to fix this issue, but I wonder if we should 
>> be
>> adding the generated ifname to the XML that is sent to the destination.
>> virDomainNetDefFormat() has this interesting piece of logic
>>
>>     if (def->ifname &&
>>         !((flags & VIR_DOMAIN_DEF_FORMAT_INACTIVE) &&
>>           (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX)))) {
>>         /* Skip auto-generated target names for inactive config. */
>>         virBufferEscapeString(buf, "<target dev='%s'/>\n", def->ifname);
>>     }
>>
>> In the Begin phase, we format the XML that will be sent to the destination 
>> based
>> on current vm->def of the machine running on the source. Calling
>> virDomainDefFormat() with VIR_DOMAIN_DEF_FORMAT_INACTIVE doesn't seem right. 
>> I
>> tried to see how this is handled in the qemu driver, but couldn't quite 
>> figure
>> it out. Jirka is one of the experts of the qemu migration code, adding him 
>> to cc
>> to see if he has any insights.
> I think this is actually handled on the destination when parsing the incoming
> XML in the Prepare phase. Something like the below patch may be a better 
> solution.

Sorry for spamming with all the self-replies...

> >From 8556bf5a116edf5989eac40f0a90feed6c003b38 Mon Sep 17 00:00:00 2001
> From: Jim Fehlig <jfehlig@xxxxxxxx>
> Date: Sun, 6 Dec 2015 10:46:28 -0700
> Subject: [PATCH] conf: add net device prefix for Xen
>
> Commit d2e5538b1 changes virDomainDef to include ifnames autogenerated
> by libxl. When migrating a domain, the autogenerated name is included
> in the XML sent to the destination host. This would lead to erronous
> behaviour (as seen in osstest CI) such as failing to migrate when
> a vif with the same name existed (belonging to another domain) on
> destination.
>
> This patch defines another VIR_NET_GENERATED_PREFIX for Xen allowing
> the autogenerated names to be excluded when parsing and formatting
> inactive config.
>
> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
> ---
>  src/conf/domain_conf.c | 6 ++++--
>  src/conf/domain_conf.h | 4 ++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 2f5c0ed..debcf4e 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -8428,7 +8428,8 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
>                  ifname = virXMLPropString(cur, "dev");
>                  if (ifname &&
>                      (flags & VIR_DOMAIN_DEF_PARSE_INACTIVE) &&
> -                    STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX)) {
> +                    (STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX) ||
> +                     STRPREFIX(ifname, VIR_NET_GENERATED_PREFIX_XEN))) {
>                      /* An auto-generated target name, blank it out */
>                      VIR_FREE(ifname);
>                  }
> @@ -19790,7 +19791,8 @@ virDomainNetDefFormat(virBufferPtr buf,
>      virBufferEscapeString(buf, "<backenddomain name='%s'/>\n", 
> def->domain_name);
>      if (def->ifname &&
>          !((flags & VIR_DOMAIN_DEF_FORMAT_INACTIVE) &&
> -          (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX)))) {
> +          (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX) ||
> +           STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX_XEN)))) {
>          /* Skip auto-generated target names for inactive config. */
>          virBufferEscapeString(buf, "<target dev='%s'/>\n", def->ifname);
>      }
> diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
> index 90d8e13..d2cc26f 100644
> --- a/src/conf/domain_conf.h
> +++ b/src/conf/domain_conf.h
> @@ -1085,6 +1085,10 @@ struct _virDomainNetDef {
>   * by libvirt, and cannot be used for a persistent network name.  */
>  # define VIR_NET_GENERATED_PREFIX "vnet"
>  
> +/* Used for prefix of ifname of any network name generated dynamically
> + * by libvirt for Xen, and cannot be used for a persistent network name.  */
> +# define VIR_NET_GENERATED_PREFIX_XEN "vif"
> +
>  typedef enum {
>      VIR_DOMAIN_CHR_DEVICE_STATE_DEFAULT = 0,
>      VIR_DOMAIN_CHR_DEVICE_STATE_CONNECTED,

If this is acceptable, the below diff should be squashed in to use the #define
instead of hardcoded "vif" in the libxl driver.

Regards,
Jim

diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
index ef92974..c5d84a4 100644
--- a/src/libxl/libxl_domain.c
+++ b/src/libxl/libxl_domain.c
@@ -734,7 +734,7 @@ libxlDomainCleanup(libxlDriverPrivatePtr driver,
         for (i = 0; i < vm->def->nnets; i++) {
             virDomainNetDefPtr net = vm->def->nets[i];
 
-            if (STRPREFIX(net->ifname, "vif"))
+            if (STRPREFIX(net->ifname, VIR_NET_GENERATED_PREFIX_XEN))
                 VIR_FREE(net->ifname);
         }
     }
@@ -918,7 +918,8 @@ libxlDomainCreateIfaceNames(virDomainDefPtr def,
libxl_domain_config *d_config)
         if (net->ifname)
             continue;
 
-        ignore_value(virAsprintf(&net->ifname, "vif%d.%d%s",
+        ignore_value(virAsprintf(&net->ifname,
+                                 VIR_NET_GENERATED_PREFIX_XEN "%d.%d%s",
                                  def->id, x_nic->devid, suffix));
     }
 }




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