[libvirt] [PATCHv3 06/10] threshold: learn a node name for a given qcow2 disk

[Peter Krempa]

On Mon, Jun 22, 2015 at 17:06:42 -0600, Eric Blake wrote:
> Implement the QMP side of asking qemu what node name it assigned
> to an arbitrary top-level device node.  Assumes that the caller
> will have already validated that the device is qcow2 backed by
> a block device, and that qemu auto-assigns node names.
> 
> * src/qemu/qemu_monitor.h (qemuMonitorNodeNameLookup): New function.
> * src/qemu/qemu_monitor.c (qemuMonitorNodeNameLookup): Likewise.
> * src/qemu/qemu_monitor_json.h (qemuMonitorJSONNodeNameLookup):
> Likewise.
> * src/qemu/qemu_monitor_json.c (qemuMonitorJSONNodeNameLookup):
> Likewise.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/qemu/qemu_monitor.c      | 15 ++++++++-
>  src/qemu/qemu_monitor.h      |  3 ++
>  src/qemu/qemu_monitor_json.c | 77 ++++++++++++++++++++++++++++++++++++++++++++
>  src/qemu/qemu_monitor_json.h |  3 ++
>  4 files changed, 97 insertions(+), 1 deletion(-)
> 

...

> @@ -3900,6 +3902,81 @@ qemuMonitorJSONDiskNameLookup(qemuMonitorPtr mon,
>  }
> 
> 
> +/* Look up the node name of the file underneath a qcow2 image.  */
> +char *
> +qemuMonitorJSONNodeNameLookup(qemuMonitorPtr mon,
> +                              const char *device)
> +{
> +    char *ret = NULL;
> +    virJSONValuePtr cmd = NULL;
> +    virJSONValuePtr reply = NULL;
> +    virJSONValuePtr devices;
> +    size_t i;
> +
> +    cmd = qemuMonitorJSONMakeCommand("query-blockstats", NULL);

Since this is yet another function that would call query-blockstats ...

> +    if (!cmd)
> +        return NULL;
> +    if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
> +        goto cleanup;
> +
> +    if (!(devices = virJSONValueObjectGetArray(reply, "return"))) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                       _("blockstats reply was missing device list"));
> +        goto cleanup;
> +    }
> +
> +    for (i = 0; i < virJSONValueArraySize(devices); i++) {
> +        virJSONValuePtr dev = virJSONValueArrayGet(devices, i);
> +        virJSONValuePtr parent;
> +        const char *thisdev;
> +        const char *node;
> +
> +        if (!dev || dev->type != VIR_JSON_TYPE_OBJECT) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                           _("blockstats entry was not in expected format"));
> +            goto cleanup;
> +        }
> +
> +        if (!(thisdev = virJSONValueObjectGetString(dev, "device"))) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                           _("blockstats entry was not in expected format"));
> +            goto cleanup;
> +        }
> +
> +        if (STRPREFIX(thisdev, QEMU_DRIVE_HOST_PREFIX))
> +            thisdev += strlen(QEMU_DRIVE_HOST_PREFIX);
> +        if (STRNEQ(thisdev, device))
> +            continue;
> +
> +        if (!(parent = virJSONValueObjectGetObject(dev, "parent"))) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR,
> +                           _("blockstats device %s missing parent node"),
> +                           device);
> +            goto cleanup;
> +        }
> +
> +        if (!(node = virJSONValueObjectGetString(parent, "node-name"))) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR,
> +                           _("node name missing for device %s"), device);
> +            goto cleanup;
> +        }
> +        ignore_value(VIR_STRDUP(ret, node));
> +        goto cleanup;
> +    }
> +
> +    /* If we get here, we didn't find the device. */
> +    virReportError(VIR_ERR_INTERNAL_ERROR,
> +                   _("unable to find node name for device %s"),
> +                   device);

... and works only on one device and thus needs to be re-called for
every single disk I'd rather see us fold this code into
qemuMonitorJSONGetOneBlockStatsInfo so that all the info can be returned
via qemuMonitorJSONGetAllBlockStatsInfo.

I'll post a series that kills qemuMonitorJSONGetBlockExtent since it's
basically the same instance.

Peter

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