Re: [RFC 3/3] qom: Improve error message in module_object_class_by_name()

[Claudio Fontana]

On 7/20/21 3:26 AM, Jose R. Ziviani wrote:
> On Mon, Jul 19, 2021 at 05:29:49PM +0200, Claudio Fontana wrote:
>> On 7/1/21 1:27 AM, Jose R. Ziviani wrote:
>>> module_object_class_by_name() calls module_load_qom_one if the object
>>> is provided by a dynamically linked library. Such library might not be
>>> available at this moment - for instance, it can be a package not yet
>>> installed. Thus, instead of assert error messages, this patch outputs
>>> more friendly messages.
>>>
>>> Current error messages:
>>> $ ./qemu-system-x86_64 -machine q35 -accel tcg -kernel /boot/vmlinuz
>>> ...
>>> ERROR:../accel/accel-softmmu.c:82:accel_init_ops_interfaces: assertion 
>>> failed: (ops != NULL)
>>> Bail out! ERROR:../accel/accel-softmmu.c:82:accel_init_ops_interfaces: 
>>> assertion failed: (ops != NULL)
>>> [1]    31964 IOT instruction (core dumped)  ./qemu-system-x86_64 ...
>>>
>>> New error message:
>>> $ ./qemu-system-x86_64 -machine q35 -accel tcg -kernel /boot/vmlinuz
>>> accel-tcg-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>>
>>> $ make check
>>> ...
>>> Running test qtest-x86_64/test-filter-mirror
>>> Running test qtest-x86_64/endianness-test
>>> accel-qtest-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> accel-qtest-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> accel-qtest-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> accel-qtest-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> accel-qtest-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> accel-tcg-x86_64 module is missing, install the package or config the 
>>> library path correctly.
>>> ...
>>>
>>> Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
>>> ---
>>>  qom/object.c | 30 ++++++++++++++++++++++++++++++
>>>  1 file changed, 30 insertions(+)
>>>
>>> diff --git a/qom/object.c b/qom/object.c
>>> index 6a01d56546..2d40245af9 100644
>>> --- a/qom/object.c
>>> +++ b/qom/object.c
>>> @@ -1024,6 +1024,24 @@ ObjectClass *object_class_by_name(const char 
>>> *typename)
>>>      return type->class;
>>>  }
>>>  
>>> +char *get_accel_module_name(const char *ac_name);
>>> +
>>> +char *get_accel_module_name(const char *ac_name)
>>> +{
>>> +    size_t len = strlen(ac_name);
>>> +    char *module_name = NULL;
>>> +
>>> +    if (strncmp(ac_name, "tcg-accel-ops", len) == 0) {
>>> +#ifdef CONFIG_TCG_MODULAR
>>> +        module_name = g_strdup_printf("%s%s", "accel-tcg-", "x86_64");
>>> +#endif
>>> +    } else if (strncmp(ac_name, "qtest-accel-ops", len) == 0) {
>>> +        module_name = g_strdup_printf("%s%s", "accel-qtest-", "x86_64");
>>> +    }
>>> +
>>> +    return module_name;
>>> +}
>>> +
>>>  ObjectClass *module_object_class_by_name(const char *typename)
>>>  {
>>>      ObjectClass *oc;
>>> @@ -1031,8 +1049,20 @@ ObjectClass *module_object_class_by_name(const char 
>>> *typename)
>>>      oc = object_class_by_name(typename);
>>>  #ifdef CONFIG_MODULES
>>>      if (!oc) {
>>> +        char *module_name;
>>>          module_load_qom_one(typename);
>>>          oc = object_class_by_name(typename);
>>> +        module_name = get_accel_module_name(typename);
>>> +        if (module_name) {
>>> +            if (!module_is_loaded(module_name)) {
>>> +                fprintf(stderr, "%s module is missing, install the "
>>> +                                "package or config the library path "
>>> +                                "correctly.\n", module_name);
>>> +                g_free(module_name);
>>> +                exit(1);
>>> +            }
>>> +            g_free(module_name);
>>> +        }
>>>      }
>>>  #endif
>>>      return oc;
>>>
>>
>> Hi Jose,
>>
>> this inserts accel logic into module_object_class_by_name,
>> maybe some other place would be better to insert this check,
>> like when trying to select an accelerator?
> 
> 
> Hello Claudio,
> 
> Yes, I think that 'get_accel_module_name()' may be a more generic
> 'get_module_name()' to handle any module failure (not only
> accelerators).
> 
> I'll improve it and send a v2. Thank you for reviewing it.
> 

I also wonder, and @Gerd , should "tcg_enabled()", tcg_allowed etc as a 
mechanism be rethought,
in light of modular TCG?

Probably would be easier to do if we had a general mechanism for CONFIG_TCG=m 
CONFIG_KVM=m ... which can separately be set as modules.

Thanks,

Claudio