Re: [Qemu-devel] [PATCH 01/20] qdev: add print_options callback

[Alon Levy]

On Thu, Feb 03, 2011 at 10:39:40AM -0600, Anthony Liguori wrote:
> On 02/02/2011 02:28 PM, Alon Levy wrote:
> >another callback added to PropertyInfo, for later use by PROP_TYPE_ENUM.
> >Allows printing of runtime computed options when doing:
> >  qemu -device foo,?
> >---
> >  hw/qdev.c |   10 +++++++++-
> >  hw/qdev.h |    1 +
> >  2 files changed, 10 insertions(+), 1 deletions(-)
> >
> >diff --git a/hw/qdev.c b/hw/qdev.c
> >index c7fec44..0b2ad3d 100644
> >--- a/hw/qdev.c
> >+++ b/hw/qdev.c
> >@@ -187,7 +187,15 @@ int qdev_device_help(QemuOpts *opts)
> >          if (!prop->info->parse) {
> >              continue;           /* no way to set it, don't show */
> >          }
> >-        error_printf("%s.%s=%s\n", info->name, prop->name, 
> >prop->info->name);
> >+        if (prop->info->print_options) {
> >+            char buf[256];
> >+            int ret;
> >+            ret = prop->info->print_options(info, prop, buf, sizeof(buf) - 
> >3);
> >+            error_printf("%s.%s=%s%s\n", info->name, prop->name, buf,
> >+                ret == sizeof(buf) - 3 ? "..." : "" );
> >+        } else {
> >+            error_printf("%s.%s=%s\n", info->name, prop->name, 
> >prop->info->name);
> >+        }
> >      }
> >      return 1;
> >  }
> >diff --git a/hw/qdev.h b/hw/qdev.h
> >index 9808f85..fa3221b 100644
> >--- a/hw/qdev.h
> >+++ b/hw/qdev.h
> >@@ -109,6 +109,7 @@ struct PropertyInfo {
> >      enum PropertyType type;
> >      int (*parse)(DeviceState *dev, Property *prop, const char *str);
> >      int (*print)(DeviceState *dev, Property *prop, char *dest, size_t len);
> >+    int (*print_options)(DeviceInfo *info, Property *prop, char *dest, 
> >size_t len);
> 
> I'm not clear what the different between print and print_options is
> and why two callbacks are needed.  Can you explain and comments to

There is a difference in usage - the existing print is called when we do info 
during
execution, it shows the status of the device. print_options is given a 
DeviceInfo
and not a DeviceState and responds with the list we print for a command line 
invocation:
"qemu -device foo,? ", It is used to allow possible options that depend on 
available
runtime libraries or other resources. It also allows relatively easy 
implementation for
data that could be known at compile time, like names for enums, used by the 
next patches.

> the patch clarifying why two interfaces are needed.  Even better
> would be if one interface could handle it.
> 
> Regards,
> 
> Anthony Liguori
> 
> 
> >      void (*free)(DeviceState *dev, Property *prop);
> >  };
> >
>