Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/07/2011 04:43 AM, Alon Levy wrote:
> On Mon, Feb 07, 2011 at 09:53:44AM +0100, Markus Armbruster wrote:
>    
>> I haven't been able to follow the evolution of this series, my apologies
>> if I'm missing things already discussed.
>>
>> Alon Levy<alevy@redhat.com>  writes:
>>
>>      
>>> Example usage:
>>>
>>> EnumTable foo_enum_table[] = {
>>>      {"bar", 1},
>>>      {"buz", 2},
>>>      {NULL, 0},
>>> };
>>>
>>> DEFINE_PROP_ENUM("foo", State, foo, 1, foo_enum_table)
>>>
>>> When using qemu -device foodev,? it will appear as:
>>>   foodev.foo=bar/buz
>>>
>>> Signed-off-by: Alon Levy<alevy@redhat.com>
>>> ---
>>>   hw/qdev-properties.c |   60 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>>   hw/qdev.h            |   15 ++++++++++++
>>>   2 files changed, 75 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/hw/qdev-properties.c b/hw/qdev-properties.c
>>> index a493087..3157721 100644
>>> --- a/hw/qdev-properties.c
>>> +++ b/hw/qdev-properties.c
>>> @@ -63,6 +63,66 @@ PropertyInfo qdev_prop_bit = {
>>>       .print = print_bit,
>>>   };
>>>
>>> +/* --- Enumeration --- */
>>> +/* Example usage:
>>> +EnumTable foo_enum_table[] = {
>>> +    {"bar", 1},
>>> +    {"buz", 2},
>>> +    {NULL, 0},
>>> +};
>>> +DEFINE_PROP_ENUM("foo", State, foo, 1, foo_enum_table),
>>> + */
>>> +static int parse_enum(DeviceState *dev, Property *prop, const char *str)
>>> +{
>>> +    uint8_t *ptr = qdev_get_prop_ptr(dev, prop);
>>>        
>> uint8_t is inconsistent with print_enum() and DEFINE_PROP_ENUM(), which
>> both use uint32_t.
>>      
> Thanks, fixing.
>
>    
>>      
>>> +    EnumTable *option = (EnumTable*)prop->data;
>>>        
>> Please don't cast from void * to pointer type (this isn't C++).
>>
>>      
> Will fix for all references.
>
>    
>> Not thrilled about the "void *data", to be honest.  Smells like
>> premature generality to me.
>>
>>      
> I did put it in there because I didn't think a "EnumTable *enum" variable
> would have been acceptable (added baggage just used by a single property type),
> and I didn't find any other place to add it. I guess I should just do a:
>
> typedef struct EnumProperty {
>      Property base;
>      EnumTable *table;
> } EnumProperty;
>
> But then because we define the properties in a Property[] array this won't work.
> Maybe turn that into a Property* array?
>
> In summary I guess data is a terrible name, but it was least amount of change. Happy
> to take suggestions.
>
>    
>>> +
>>> +    while (option->name != NULL) {
>>> +        if (!strncmp(str, option->name, strlen(option->name))) {
>>>        
>> Why strncmp() and not straight strcmp()?
>>
>>      
> I guess no reason except "strncmp is more secure" but irrelevant here since
> option->name is from the source, I'll fix.
>
>    
>>> +            *ptr = option->value;
>>> +            return 0;
>>> +        }
>>> +        option++;
>>> +    }
>>> +    return -EINVAL;
>>> +}
>>> +
>>> +static int print_enum(DeviceState *dev, Property *prop, char *dest, size_t len)
>>> +{
>>> +    uint32_t *p = qdev_get_prop_ptr(dev, prop);
>>> +    EnumTable *option = (EnumTable*)prop->data;
>>> +    while (option->name != NULL) {
>>> +        if (*p == option->value) {
>>> +            return snprintf(dest, len, "%s", option->name);
>>> +        }
>>> +        option++;
>>> +    }
>>> +    return 0;
>>>        
>> Bug: must dest[0] = 0 when returning 0.
>>
>>      
> will just return snprintf(dest, len, "<enum %d>", option->value)
>
>    
>>> +}
>>> +
>>> +static int print_enum_options(DeviceInfo *info, Property *prop, char *dest, size_t len)
>>> +{
>>> +    int ret = 0;
>>> +    EnumTable *option = (EnumTable*)prop->data;
>>>        
>> Please don't cast from void * to pointer type (this isn't C++).
>>
>>      
> fixing.
>
>    
>>> +    while (option->name != NULL) {
>>> +        ret += snprintf(dest + ret, len - ret, "%s", option->name);
>>> +        if (option[1].name != NULL) {
>>> +            ret += snprintf(dest + ret, len - ret, "/");
>>> +        }
>>> +        option++;
>>> +    }
>>> +    return ret;
>>> +}
>>> +
>>> +PropertyInfo qdev_prop_enum = {
>>> +    .name  = "enum",
>>> +    .type  = PROP_TYPE_ENUM,
>>> +    .size  = sizeof(uint32_t),
>>> +    .parse = parse_enum,
>>> +    .print = print_enum,
>>> +    .print_options = print_enum_options,
>>> +};
>>> +
>>>   /* --- 8bit integer --- */
>>>
>>>   static int parse_uint8(DeviceState *dev, Property *prop, const char *str)
>>> diff --git a/hw/qdev.h b/hw/qdev.h
>>> index 3d9acd7..3701d83 100644
>>> --- a/hw/qdev.h
>>> +++ b/hw/qdev.h
>>> @@ -102,6 +102,7 @@ enum PropertyType {
>>>       PROP_TYPE_VLAN,
>>>       PROP_TYPE_PTR,
>>>       PROP_TYPE_BIT,
>>> +    PROP_TYPE_ENUM,
>>>   };
>>>
>>>   struct PropertyInfo {
>>> @@ -121,6 +122,11 @@ typedef struct GlobalProperty {
>>>       QTAILQ_ENTRY(GlobalProperty) next;
>>>   } GlobalProperty;
>>>
>>> +typedef struct EnumTable {
>>> +    const char *name;
>>> +    uint32_t    value;
>>> +} EnumTable;
>>> +
>>>   /*** Board API.  This should go away once we have a machine config file.  ***/
>>>
>>>   DeviceState *qdev_create(BusState *bus, const char *name);
>>> @@ -235,6 +241,7 @@ extern PropertyInfo qdev_prop_drive;
>>>   extern PropertyInfo qdev_prop_netdev;
>>>   extern PropertyInfo qdev_prop_vlan;
>>>   extern PropertyInfo qdev_prop_pci_devfn;
>>> +extern PropertyInfo qdev_prop_enum;
>>>
>>>   #define DEFINE_PROP(_name, _state, _field, _prop, _type) { \
>>>           .name      = (_name),                                    \
>>> @@ -257,6 +264,14 @@ extern PropertyInfo qdev_prop_pci_devfn;
>>>               + type_check(uint32_t,typeof_field(_state, _field)), \
>>>           .defval    = (bool[]) { (_defval) },                     \
>>>           }
>>> +#define DEFINE_PROP_ENUM(_name, _state, _field, _defval, _options) {    \
>>> +        .name      = (_name),                                           \
>>> +        .info      =&(qdev_prop_enum),                                 \
>>> +        .offset    = offsetof(_state, _field)                           \
>>> +            + type_check(uint32_t,typeof_field(_state, _field)),        \
>>> +        .defval    = (uint32_t[]) { (_defval) },                        \
>>> +        .data      = (void*)(_options),                                 \
>>>        
>> Please don't cast from pointer type to void * (this isn't C++).  If
>> someone accidentally passes an integral argument for _options (forgotten
>> operator&), the cast suppresses the warning.
>>
>>      
> fixing.
>
>    
>>> +        }
>>>
>>>   #define DEFINE_PROP_UINT8(_n, _s, _f, _d)                       \
>>>       DEFINE_PROP_DEFAULT(_n, _s, _f, _d, qdev_prop_uint8, uint8_t)
>>>        
>> Okay, let's examine how your enumeration properties work.
>>
>> An enumeration property describes a uint32_t field of the state object.
>> Differences to ordinary properties defined with DEFINE_PROP_UINT32:
>>
>> * info is qdev_prop_enum instead of qdev_prop_uint32.  Differences
>>    between the two:
>>
>>    - parse, print: symbolic names vs. numbers
>>
>>    - name, print_options: only for -device DRIVER,\? (and name's use
>>      there isn't particularly helpful)
>>      
> Why do you say that? this is being used by libvirt to get the names of the
> supported backends for the ccid-card-emulated device.
>    

This is wrong.

Libvirt should query this information through QMP.  This is my main 
concern with enums.  If there isn't a useful introspection interface, 
libvirt is going to do dumb things like query help output.

This has been a nightmare historically and I'm not inclined to repeat it.

Regards,

Anthony Liguori