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

[Alon Levy]

On Mon, Feb 07, 2011 at 07:15:57AM -0600, Anthony Liguori wrote:
> 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<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?
> >
> >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.
> 

Fair enough, so a patch that added enumeration through QMP would be acceptable?
I'm not even sure that makes sense, would you mind outlining how you see this
implemented?

> Regards,
> 
> Anthony Liguori
> 
>