Re: [PATCH] qemu: get VM's ip address from the output of arp command

[Martin Kletzander <mkletzan@xxxxxxxxxx>]

On Tue, Jan 23, 2018 at 03:40:02PM +0800, Chen Hanxiao wrote:
> From: Chen Hanxiao <chenhanxiao@xxxxxxxxx>
>
> Introduce VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_ARP to get ip address
> of VM from the output of `arp -an` command.

I'm not sure about the implications of this as sometimes we can't use that, but
I guess that's fine.

> We can use:
>  domifaddr f26-cloud --source arp
> to get the address.
>
> Signed-off-by: Chen Hanxiao <chenhanxiao@xxxxxxxxx>
> ---
> include/libvirt/libvirt-domain.h |   1 +
> src/qemu/qemu_driver.c           | 102 +++++++++++++++++++++++++++++++++++++++
> tools/virsh-domain-monitor.c     |   2 +
> 3 files changed, 105 insertions(+)

I see no documentation changes here.

> diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
> index 4048acf38..38e2d9a3e 100644
> --- a/include/libvirt/libvirt-domain.h
> +++ b/include/libvirt/libvirt-domain.h
> @@ -4665,6 +4665,7 @@ typedef virMemoryParameter *virMemoryParameterPtr;
> typedef enum {
>     VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_LEASE = 0, /* Parse DHCP lease file */
>     VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_AGENT = 1, /* Query qemu guest agent */
> +    VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_ARP = 2, /* Query ARP tables */
>
> # ifdef VIR_ENUM_SENTINELS
>     VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_LAST
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index a203c9297..5aaf69442 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -160,6 +160,9 @@ static int qemuGetDHCPInterfaces(virDomainPtr dom,
>                                  virDomainObjPtr vm,
>                                  virDomainInterfacePtr **ifaces);
>
> +static int qemuARPGetInterfaces(virDomainObjPtr vm,
> +                                virDomainInterfacePtr **ifaces);
> +
> static virQEMUDriverPtr qemu_driver;
>
>
> @@ -20384,6 +20387,10 @@ qemuDomainInterfaceAddresses(virDomainPtr dom,
>
>         break;
>
> +    case VIR_DOMAIN_INTERFACE_ADDRESSES_SRC_ARP:
> +        ret = qemuARPGetInterfaces(vm, ifaces);
> +        break;
> +
>     default:
>         virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED,
>                        _("Unknown IP address data source %d"),
> @@ -20494,6 +20501,101 @@ qemuGetDHCPInterfaces(virDomainPtr dom,
> }
>
>
> +static int
> +qemuARPGetInterfaces(virDomainObjPtr vm,
> +                     virDomainInterfacePtr **ifaces)
> +{
> +    size_t i, j;
> +    size_t ifaces_count = 0;
> +    int ret = -1;
> +    char macaddr[VIR_MAC_STRING_BUFLEN];
> +    virDomainInterfacePtr *ifaces_ret = NULL;
> +    virDomainInterfacePtr iface = NULL;
> +    virCommandPtr cmd = NULL;
> +    char *outbuf;
> +    char **lines = NULL;
> +    char **matches = NULL;
> +#define ARP_CMD "/usr/sbin/arp"
> +

I think this should be determined like other programs in
`m4/virt-external-programs.m4`.

But rather than this, is this supported under non-Linux?  I don't know how arp
works elsewhere, but for Linux we could just parse /proc/net/arp ourselves.

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