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Date: Thu, 01 Dec 2011 17:14:37 +0100
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 02/18] qom: register legacy properties as
	new style properties
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Jan Kiszka <jan.kiszka@siemens.com>, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>

Am 30.11.2011 22:03, schrieb Anthony Liguori:
> Expose all legacy properties through the new QOM property mechanism.  The qdev
> property types are exposed through the 'legacy<>' namespace.  They are always
> visited as strings since they do their own string parsing.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> ---
>  hw/qdev.c |   82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/qdev.h |    7 +++++
>  2 files changed, 89 insertions(+), 0 deletions(-)

Not directly related to this patch, but looking for the first time at
visitor code, visitors are clearly underdocumented.

> +static void qdev_get_legacy_property(DeviceState *dev, Visitor *v, void *opaque,
> +                                     const char *name, Error **errp)
> +{
> +    Property *prop = opaque;
> +
> +    if (prop->info->print) {
> +        char buffer[1024];
> +        char *ptr = buffer;
> +
> +        prop->info->print(dev, prop, buffer, sizeof(buffer));
> +        visit_type_str(v, &ptr, name, errp);

So a string output visitor (this is what it's called, right?) takes a
buffer on the stack that the visitor must not free...

> +    } else {
> +        error_set(errp, QERR_PERMISSION_DENIED);
> +    }
> +}
> +
> +static void qdev_set_legacy_property(DeviceState *dev, Visitor *v, void *opaque,
> +                                     const char *name, Error **errp)
> +{
> +    Property *prop = opaque;
> +
> +    if (dev->state != DEV_STATE_CREATED) {
> +        error_set(errp, QERR_PERMISSION_DENIED);
> +        return;
> +    }
> +
> +    if (prop->info->parse) {
> +        Error *local_err = NULL;
> +        char *ptr = NULL;
> +
> +        visit_type_str(v, &ptr, name, &local_err);
> +        if (!local_err) {
> +            int ret;
> +            ret = prop->info->parse(dev, prop, ptr);
> +            if (ret != 0) {
> +                error_set(errp, QERR_INVALID_PARAMETER_VALUE,
> +                          name, prop->info->name);
> +            }
> +            g_free(ptr);

...but a string input visitor creates a copy that must be freed.

Kind of surprising behaviour, and qapi-visit-core.h doesn't document it.

Kevin