Re: [PATCH] qemu_monitor_json: add support to search QOM device path by device alias

[Martin Kletzander <mkletzan@xxxxxxxxxx>]

On Mon, Jul 25, 2016 at 02:41:01PM +0200, Pavel Hrdina wrote:
> Commit ce745914 introduced detection of actual video ram sizes to fix migration
> if QEMU decide to modify the values provided by libvirt.  This works perfectly
> for domains with number of video devices up to two.
>
> If there are more than two video devices in the guest all the secondary devices
> in the XML will have the same memory values.  This is because our current code
> search for QOM device path only by the device type name and all the secondary
> video devices has the same name "qxl".
>
> This patch introduces a new search function that will try to search a QOM device
> path using also device's alias if the alias is available. After that it will
> fallback to the old recursive code if the alias search found no results.
>
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1358728
>
> Signed-off-by: Pavel Hrdina <phrdina@xxxxxxxxxx>
> ---
> src/qemu/qemu_monitor.c      | 11 ++++---
> src/qemu/qemu_monitor_json.c | 74 ++++++++++++++++++++++++++++++++++++++------
> src/qemu/qemu_monitor_json.h |  3 +-
> 3 files changed, 74 insertions(+), 14 deletions(-)
>
> diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> index 098e654..1fac4de 100644
> --- a/src/qemu/qemu_monitor.c
> +++ b/src/qemu/qemu_monitor.c
> @@ -1084,10 +1084,11 @@ qemuMonitorInitBalloonObjectPath(qemuMonitorPtr mon)
>     }
>     mon->ballooninit = true;
>
> -    flp_ret = qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-pci", &path);
> +    flp_ret = qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-pci", NULL, &path);
>     if (flp_ret == -2) {
>         /* pci object was not found retry search for ccw object */
> -        if (qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-ccw", &path) < 0)
> +        if (qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-ccw",
> +                                        NULL, &path) < 0)

We could pass the balloon alias here through all the functions, right?
Although it will be literally 'balloon0' every single time there is any,
so maybe we could use that.

> diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
> index bb426dc..5d24e26 100644
> --- a/src/qemu/qemu_monitor_json.c
> +++ b/src/qemu/qemu_monitor_json.c
> @@ -6810,7 +6810,55 @@ qemuMonitorJSONGetMemoryDeviceInfo(qemuMonitorPtr mon,
>
>
> /**
> - * Recursively search for a QOM object link.
> + * Search for a QOM object link by alias and name.
> + *
> + * For @alias and @name, this function tries to find QOM object named @name
> + * with id @alias in /machine/peripheral.
> + *
> + * Returns:
> + *   0  - Found
> + *  -1  - Error - bail out
> + *  -2  - Not found
> + */
> +static int
> +qemuMonitorJSONFindObjectPathByAlias(qemuMonitorPtr mon,
> +                                     const char *name,
> +                                     const char *alias,
> +                                     char **path)
> +{
> +    qemuMonitorJSONListPathPtr *paths = NULL;
> +    char *child = NULL;
> +    int npaths;
> +    int ret = -1;
> +    size_t i;
> +
> +    npaths = qemuMonitorJSONGetObjectListPaths(mon, "/machine/peripheral", &paths);
> +    if (npaths < 0)
> +        return -1;
> +
> +    if (virAsprintf(&child, "child<%s>", name) < 0)
> +        return -1;
> +
> +    for (i = 0; i < npaths; i++) {
> +        if (STREQ(paths[i]->name, alias) && STREQ(paths[i]->type, child)) {
> +            if (virAsprintf(path, "/machine/peripheral/%s", alias) < 0)
> +                goto cleanup;
> +
> +            ret = 0;
> +            goto cleanup;
> +        }
> +    }
> +
> +    ret = -2;
> +
> + cleanup:
> +    VIR_FREE(child);
> +    return ret;
> +}
> +

You are missing qemuMonitorJSONListPathFree() here (and also the returns
above need to be fixed).

ACK with that fixed.

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