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Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM
From: |
Alon Levy |
Subject: |
Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM |
Date: |
Mon, 7 Feb 2011 16:27:21 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Feb 07, 2011 at 03:00:25PM +0100, Markus Armbruster wrote:
> Alon Levy <address@hidden> 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 <address@hidden> 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 <address@hidden>
> >> > ---
> >> > 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?
>
I would.
> >> > +
> >> > + 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".
>
Agreed.
> >> > +}
> >> > +
> [...]
> >> > + }
> >> >
> >> > #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.
>
Right, you get strange "X=X" output most of the time, but with print_options
for enum types you actually get this:
$ x86_64-softmmu/qemu-system-x86_64 -device ccid-card-emulated,?
ccid-card-emulated.backend=nss-emulated/certificates
That's actually parsable. Of course I agree with Anthony that having a json
(QMP)
interface with properly quoted strings (here I don't take care of backslashes
in the EnumTable names for instance) would be much better.
> >>
> >> * 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.
>
Ok, I can try that. Sounds like it should work.
> Note to maintainer: we don't have to get enum properties 100% right and
> polished before we can commit this series.
>
- [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, (continued)
- [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Alon Levy, 2011/02/03
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Markus Armbruster, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Alon Levy, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Anthony Liguori, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Markus Armbruster, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Anthony Liguori, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Alon Levy, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Anthony Liguori, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Anthony Liguori, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Markus Armbruster, 2011/02/07
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM,
Alon Levy <=
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Alon Levy, 2011/02/08
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Markus Armbruster, 2011/02/08
- Re: [Qemu-devel] [PATCH 03/16] qdev-properties: add PROP_TYPE_ENUM, Anthony Liguori, 2011/02/07
- [Qemu-devel] [PATCH 04/16] qdev-properties: parse_enum: don't cast a void*, Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 06/16] introduce libcacard/vscard_common.h, Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 05/16] usb-ccid: add CCID bus, Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 07/16] ccid: add passthru card device, Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 10/16] ccid: add docs, Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 09/16] ccid: add ccid-card-emulated device (v2), Alon Levy, 2011/02/03
- [Qemu-devel] [PATCH 12/16] ccid: add qdev description strings, Alon Levy, 2011/02/03