getstats: add block.n.path stat

I'm about to make block stats optionally more complex to cover
backing chains, where block.count will no longer equal the number
of <disks> for a domain.  For these reasons, it is nicer if the
statistics output includes the source path (for local files).
This patch doesn't add anything for network disks, although we
may decide to add that later.

With this patch, I now see the following for the same domain as
in the previous patch (one qcow2 file, and an empty cdrom drive):
$ virsh domstats --block foo
Domain: 'foo'
  block.count=2
  block.0.name=hda
  block.0.path=/var/lib/libvirt/images/foo.qcow2
  block.1.name=hdc

* src/libvirt-domain.c (virConnectGetAllDomainStats): Document
new field.
* tools/virsh.pod (domstats): Document new field.
* src/qemu/qemu_driver.c (qemuDomainGetStatsBlock): Return the new
stat for local files/block devices.
(QEMU_ADD_NAME_PARAM): Add parameter.
(qemuDomainGetStatsInterface): Update caller.
Signed-off-by: NEric Blake <eblake@redhat.com>

src/libvirt-domain.c

@@ -10910,6 +10910,9 @@ virConnectGetDomainCapabilities(virConnectPtr conn,
  * "block.<num>.name" - name of the block device <num> as string.
  *                      matches the target name (vda/sda/hda) of the
  *                      block device.
+ * "block.<num>.path" - string describing the source of block device <num>,
+ *                      if it is a file or block device (omitted for network
+ *                      sources and drives with no media inserted).
  * "block.<num>.rd.reqs" - number of read requests as unsigned long long.
  * "block.<num>.rd.bytes" - number of read bytes as unsigned long long.
  * "block.<num>.rd.times" - total time (ns) spent on reads as

src/qemu/qemu_driver.c

@@ -18374,11 +18374,11 @@ do { \
         goto cleanup; \
 } while (0)
 
-#define QEMU_ADD_NAME_PARAM(record, maxparams, type, num, name) \
+#define QEMU_ADD_NAME_PARAM(record, maxparams, type, subtype, num, name) \
 do { \
     char param_name[VIR_TYPED_PARAM_FIELD_LENGTH]; \
     snprintf(param_name, VIR_TYPED_PARAM_FIELD_LENGTH, \
-             "%s.%zu.name", type, num); \
+             "%s.%zu.%s", type, num, subtype); \
     if (virTypedParamsAddString(&(record)->params, \
                                 &(record)->nparams, \
                                 maxparams, \
@@ -18424,7 +18424,7 @@ qemuDomainGetStatsInterface(virQEMUDriverPtr driver ATTRIBUTE_UNUSED,
         memset(&tmp, 0, sizeof(tmp));
 
         QEMU_ADD_NAME_PARAM(record, maxparams,
-                            "net", i, dom->def->nets[i]->ifname);
+                            "net", "name", i, dom->def->nets[i]->ifname);
 
         if (virNetInterfaceStats(dom->def->nets[i]->ifname, &tmp) < 0) {
             virResetLastError();
@@ -18517,7 +18517,10 @@ qemuDomainGetStatsBlock(virQEMUDriverPtr driver,
         qemuBlockStats *entry;
         virDomainDiskDefPtr disk = dom->def->disks[i];
 
-        QEMU_ADD_NAME_PARAM(record, maxparams, "block", i, disk->dst);
+        QEMU_ADD_NAME_PARAM(record, maxparams, "block", "name", i, disk->dst);
+        if (virStorageSourceIsLocalStorage(disk->src) && disk->src->path)
+            QEMU_ADD_NAME_PARAM(record, maxparams, "block", "path",
+                                i, disk->src->path);
 
         if (abbreviated || !disk->info.alias ||
             !(entry = virHashLookup(stats, disk->info.alias))) {

tools/virsh.pod

@@ -883,6 +883,8 @@ I<--interface> returns:
 I<--block> returns:
 "block.count" - number of block devices on this domain,
 "block.<num>.name" - name of the target of the block device <num>,
+"block.<num>.path" - file source of block device <num>, if it is a
+local file or block device,
 "block.<num>.rd.reqs" - number of read requests,
 "block.<num>.rd.bytes" - number of read bytes,
 "block.<num>.rd.times" - total time (ns) spent on reads,