Re: [Qemu-devel] [PATCH] monitor: allow object_del & device_del to accept QOM paths

[Markus Armbruster]

Copying Andreas and Paolo for QOM expertise.

"Daniel P. Berrange" <address@hidden> writes:

> Currently both object_del and device_del require that the
> client provide the object/device short ID. While user
> creatable objects require an ID to be provided at time of
> creation, qdev devices may be created without giving an
> ID. The only unique identifier they would then have is the
> QOM object path.
>
> Allowing device_del to accept an object path ensures all
> devices are deletable regardless of whether they have an
> ID.
>
>  (qemu) device_add usb-mouse
>  (qemu) qom-list /machine/peripheral-anon
>  device[0] (child<usb-mouse>)
>  type (string)
>  (qemu) device_del /machine/peripheral-anon/device[0]
>
> Although objects require an ID to be provided upfront,
> there may be cases where the client would prefer to
> use QOM paths when deleting.
>
> Signed-off-by: Daniel P. Berrange <address@hidden>

I believe this makes sense no matter what we do about device IDs (see
thread "Should we auto-generate IDs?").

> ---
>  hmp-commands.hx |  6 ++++--
>  qdev-monitor.c  | 14 +++++++++-----
>  qmp-commands.hx | 17 +++++++++++++----
>  qmp.c           | 10 +++++++---
>  4 files changed, 33 insertions(+), 14 deletions(-)
>
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index d3b7932..c0c113d 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -675,7 +675,8 @@ ETEXI
>  STEXI
>  @item device_del @var{id}
>  @findex device_del
> -Remove device @var{id}.
> +Remove device @var{id}. @var{id} may be a short ID
> +or a QOM object path.
>  ETEXI
>  
>      {
> @@ -1279,7 +1280,8 @@ ETEXI
>  STEXI
>  @item object_del
>  @findex object_del
> -Destroy QOM object.
> +Destroy QOM object. @var{id} may be a short ID
> +or a QOM object path.
>  ETEXI
>  
>  #ifdef CONFIG_SLIRP
> diff --git a/qdev-monitor.c b/qdev-monitor.c
> index f9e2d62..894b799 100644
> --- a/qdev-monitor.c
> +++ b/qdev-monitor.c
> @@ -785,13 +785,17 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, 
> Error **errp)
>  void qmp_device_del(const char *id, Error **errp)
>  {
>      Object *obj;
> -    char *root_path = object_get_canonical_path(qdev_get_peripheral());
> -    char *path = g_strdup_printf("%s/%s", root_path, id);
>  
> -    g_free(root_path);
> -    obj = object_resolve_path_type(path, TYPE_DEVICE, NULL);
> -    g_free(path);
> +    if (id[0] == '/') {
> +        obj = object_resolve_path(id, NULL);
> +    } else {
> +        char *root_path = object_get_canonical_path(qdev_get_peripheral());
> +        char *path = g_strdup_printf("%s/%s", root_path, id);
>  
> +        g_free(root_path);
> +        obj = object_resolve_path_type(path, TYPE_DEVICE, NULL);
> +        g_free(path);
> +    }
>      if (!obj) {
>          error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
>                    "Device '%s' not found", id);

Easier to review with whitespace change ignored:

    diff --git a/qdev-monitor.c b/qdev-monitor.c
    index f9e2d62..894b799 100644
    --- a/qdev-monitor.c
    +++ b/qdev-monitor.c
    @@ -785,13 +785,17 @@
     void qmp_device_del(const char *id, Error **errp)
     {
         Object *obj;
    +
    +    if (id[0] == '/') {
    +        obj = object_resolve_path(id, NULL);
    +    } else {
         char *root_path = object_get_canonical_path(qdev_get_peripheral());
         char *path = g_strdup_printf("%s/%s", root_path, id);

         g_free(root_path);
         obj = object_resolve_path_type(path, TYPE_DEVICE, NULL);
         g_free(path);
    -
    +    }
         if (!obj) {
             error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
                       "Device '%s' not found", id);

I'd keep the blank line between the code finding obj and the if (!obj)
error check.

@id is a suboptimal name now, but changing it isn't worth the churn.

> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index ba630b1..d3070cf 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -321,14 +321,19 @@ Remove a device.
>  
>  Arguments:
>  
> -- "id": the device's ID (json-string)
> -
> +- "id": the device's ID or QOM path (json-string)
> +EQ
>  Example:
>  
>  -> { "execute": "device_del", "arguments": { "id": "net1" } }
>  <- { "return": {} }
>  
> -EQMP
> +Example:
> +
> +-> { "execute": "device_del", "arguments": { "id": 
> "/machine/peripheral-anon/device[0]" } }
> +<- { "return": {} }
> +
> +MP
>  
>      {
>          .name       = "send-key",
> @@ -965,7 +970,7 @@ Remove QOM object.
>  
>  Arguments:
>  
> -- "id": the object's ID (json-string)
> +- "id": the object's ID or QOM path (json-string)
>  
>  Example:
>  
> @@ -973,6 +978,10 @@ Example:
>  <- { "return": {} }
>  
>  
> +-> { "execute": "object-del", "arguments": { "id": "/objects/hostmem1" } }
> +<- { "return": {} }
> +
> +
>  EQMP
>  
>  

Thanks for adding examples.

As Eric said, you should also update qapi-schema.json.

The duplication is unfortunate.  There's an RFC PATCH series from
Marc-André pending review, which should get us one step closer to
killing qmp-commands.hx.

> diff --git a/qmp.c b/qmp.c
> index 403805a..11e9f51 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -678,11 +678,15 @@ void qmp_object_add(QDict *qdict, QObject **ret, Error 
> **errp)
>  
>  void qmp_object_del(const char *id, Error **errp)
>  {
> -    Object *container;
>      Object *obj;
>  
> -    container = object_get_objects_root();
> -    obj = object_resolve_path_component(container, id);
> +    if (id[0] == '/') {
> +        obj = object_resolve_path(id, NULL);
> +    } else {
> +        Object *container;
> +        container = object_get_objects_root();
> +        obj = object_resolve_path_component(container, id);
> +    }
>      if (!obj) {
>          error_setg(errp, "object id not found");
>          return;

Ignoring whitespace change:

    diff --git a/qmp.c b/qmp.c
    index 403805a..11e9f51 100644
    --- a/qmp.c
    +++ b/qmp.c
    @@ -678,11 +678,15 @@

     void qmp_object_del(const char *id, Error **errp)
     {
    -    Object *container;
         Object *obj;

    +    if (id[0] == '/') {
    +        obj = object_resolve_path(id, NULL);
    +    } else {
    +        Object *container;
         container = object_get_objects_root();
         obj = object_resolve_path_component(container, id);
    +    }
         if (!obj) {
             error_setg(errp, "object id not found");
             return;

I'd keep container right where it is.  We generally prefer keeping
declarations at the beginning of the function body, at least for small
functions.

Update qapi-schema.json updated the obvious way, and you can have my
R-by.  Also addressing my stylistic nitpicks would be nice.

Thanks for tackling this, it's long overdue!