Alon Levy <al...@redhat.com> writes:
> 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 <al...@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 <al...@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?
Doubt the additional complexity just for keeping EnumTable out of
Property is worth it.
> In summary I guess data is a terrible name, but it was least amount of
> change. Happy
> to take suggestions.
Further down, we discuss the idea of supporting an EnumTable with
arbitrary integer type properties. Would you find an EnumTable member
of Property more palatable then?
>> > +
>> > + 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)
Print something useful is a good idea. I guess I'd print an unadorned
"%d".
>> > +}
>> > +
[...]
>> > + }
>> >
>> > #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.
Too terse, let me try again :)
- name, print_options: differences not important here, because these
members are they are only for -device DRIVER,\?
By the way, I don't find help output like
e1000.mac=macaddr
e1000.vlan=vlan
e1000.netdev=netdev
particularly helpful. Not your fault, outside the scope of this
patch.
>>
>> * data points to an EnumTable, which is a map string <-> number. Thus,
>> the actual enumeration is attached to the property declaration, not
>> the property type (in programming languages, we commonly attach it to
>> the type, not the variable declaration). Since it's a table it can be
>> used for multiple properties with minimal fuss. Works for me.
>>
>> What if we want to enumerate values of fields with types other than
>> uint32_t?
>>
>> C enumeration types, in particular. Tricky, because width and
>> signedness of enum types is implementation-defined, and different enum
>> types may differ there.
>>
>
> I specifically used uint32_t expecting it to work for many uses. It would
> be better to allow an arbitrary type, or just not require specifying the
> type but getting it from the enum itself (using typeof?). But then you
> can't have a single EnumTable because it's type is now dependent on the
> enumeration type (of course I could resort to macros, but I don't want to
> go there).
That's what I meant when I called it "tricky".
Still, having an enum property that cannot be used with enumeration
types is kind of sad, isn't it?
>> Perhaps what we really need is a way to define arbitrary integer type
>> properties with an EnumTable attached.
>>
>
> This sounds more promising. So you would have an EnumTableU32 etc and
> DEFINE_PROP_{UINT8,..}_ENUM which takes an extra EnumTable of the correct
> type, to be defined inline maybe so user doesn't actually declare it (like
> no one declares Property thanks to the DEFINE_PROP_ macros).
Sounds like what I have in mind. Care to explore it?
One EnumTable should do, just make its member value wide enough.
Note to maintainer: we don't have to get enum properties 100% right and
polished before we can commit this series.
