Re: [Qemu-devel] [PATCH 35/35] docs: writing-qmp-commands.txt: update error section

[Luiz Capitulino]

On Wed, 08 Aug 2012 14:35:23 +0200
Pavel Hrdina <address@hidden> wrote:

> On 08/07/2012 05:53 PM, Luiz Capitulino wrote:
> > Add information about the new error format and improve the text a bit.
> >
> > Signed-off-by: Luiz Capitulino <address@hidden>
> > ---
> >   docs/writing-qmp-commands.txt | 47 
> > +++++++++++++++++++++++++------------------
> >   1 file changed, 27 insertions(+), 20 deletions(-)
> >
> > diff --git a/docs/writing-qmp-commands.txt b/docs/writing-qmp-commands.txt
> > index 0ad51aa..10ecd97 100644
> > --- a/docs/writing-qmp-commands.txt
> > +++ b/docs/writing-qmp-commands.txt
> > @@ -210,19 +210,17 @@ if you don't see these strings, then something went 
> > wrong.
> >   === Errors ===
> >   
> >   QMP commands should use the error interface exported by the error.h header
> > -file. The basic function used to set an error is the error_set() one.
> > +file. Basically, errors are set by calling the error_set() function.
> >   
> >   Let's say we don't accept the string "message" to contain the word 
> > "love". If
> > -it does contain it, we want the "hello-world" command to the return the
> > -InvalidParameter error.
> > -
> > -Only one change is required, and it's in the C implementation:
> > +it does contain it, we want the "hello-world" command to return an error:
> >   
> >   void qmp_hello_world(bool has_message, const char *message, Error **errp)
> >   {
> >       if (has_message) {
> >           if (strstr(message, "love")) {
> > -            error_set(errp, QERR_INVALID_PARAMETER, "message");
> > +            error_set(errp, ERROR_CLASS_GENERIC_ERROR,
> > +                      "the word 'love' is not allowed");
> >               return;
> >           }
> >           printf("%s\n", message);
> > @@ -231,30 +229,40 @@ void qmp_hello_world(bool has_message, const char 
> > *message, Error **errp)
> >       }
> >   }
> >   
> > -Let's test it. Build qemu, run it as defined in the "Testing" section, and
> > -then issue the following command:
> > +The first argument to the error_set() function is the Error pointer to 
> > pointer,
> > +which is passed to all QMP functions. The second argument is a ErrorClass
> > +value, which should be ERROR_CLASS_GENERIC_ERROR most of the time (more
> > +details about error classes are given below). The third argument is a human
> > +description of the error, this is a free-form printf-like string.
> > +
> > +Let's test the example above. Build qemu, run it as defined in the 
> > "Testing"
> > +section, and then issue the following command:
> >   
> > -{ "execute": "hello-world", "arguments": { "message": "we love qemu" } }
> > +{ "execute": "hello-world", "arguments": { "message": "all you need is 
> > love" } }
> >   
> >   The QMP server's response should be:
> >   
> >   {
> >       "error": {
> > -        "class": "InvalidParameter",
> > -        "desc": "Invalid parameter 'message'",
> > -        "data": {
> > -            "name": "message"
> > -        }
> > +        "class": "GenericError",
> 
> you have here trailing white-space  ^

I've fixed it for v3, thanks.

> 
> > +        "desc": "the word 'love' is not allowed"
> >       }
> >   }
> >   
> > -Which is the InvalidParameter error.
> > +As a general rule, all QMP errors should use ERROR_CLASS_GENERIC_ERROR. 
> > There
> > +are two exceptions to this rule:
> > +
> > + 1. A non-generic ErrorClass value exists* for the failure you want to 
> > report
> > +    (eg. DeviceNotFound)
> > +
> > + 2. Management applications have to take special action on the failure you
> > +    want to report, hence you have to add a new ErrorClass value so that 
> > they
> > +    can check for it
> >   
> > -When you have to return an error but you're unsure what error to return or
> > -which arguments an error takes, you should look at the qerror.h file. Note
> > -that you might be required to add new errors if needed.
> > +If the failure you want to report doesn't fall in one of the two cases 
> > above,
> > +just report ERROR_CLASS_GENERIC_ERROR.
> >   
> > -FIXME: describe better the error API and how to add new errors.
> > + * All existing ErrorClass values are defined in the qapi-schema.json file
> >   
> >   === Command Documentation ===
> >   
> > @@ -275,7 +283,6 @@ here goes "hello-world"'s new entry for the 
> > qapi-schema.json file:
> >   # @message: #optional string to be printed
> >   #
> >   # Returns: Nothing on success.
> > -#          If @message contains "love", InvalidParameter
> >   #
> >   # Notes: if @message is not provided, the "Hello, world" string will
> >   #        be printed instead
>