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

[Martin Kletzander]

On Tue, Jan 23, 2018 at 03:40:02PM +0800, Chen Hanxiao wrote:

From: Chen Hanxiao <chenhanx...@gmail.com>

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 <chenhanx...@gmail.com>
---
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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