Re: [Qemu-devel] [RFC 1/2] qbus_find_recursive(): don't abort search for named bus on full bus node

[Peter Maydell]

On 31 January 2013 15:58, KONRAD Frédéric <address@hidden> wrote:
> On 31/01/2013 16:52, Peter Maydell wrote:
>>
>> On 31 January 2013 15:42, Laszlo Ersek <address@hidden> wrote:
>>>
>>> The bus we're looking for could be in the sub-tree rooted at the node
>>> being checked; don't skip looping over the children.
>>>
>>> Signed-off-by: Laszlo Ersek <address@hidden>
>>> ---
>>>   hw/qdev-monitor.c |   10 +--------
>>>   1 files changed, 1 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/hw/qdev-monitor.c b/hw/qdev-monitor.c
>>> index 4e2a92b..34f5014 100644
>>> --- a/hw/qdev-monitor.c
>>> +++ b/hw/qdev-monitor.c
>>> @@ -295,15 +295,7 @@ static BusState *qbus_find_recursive(BusState *bus,
>>> const char *name,
>>>           match = 0;
>>>       }
>>>       if ((bus_class->max_dev != 0) && (bus_class->max_dev <=
>>> bus->max_index)) {
>>> -        if (name != NULL) {
>>> -            /* bus was explicitly specified: return an error. */
>>> -            qerror_report(ERROR_CLASS_GENERIC_ERROR, "Bus '%s' is full",
>>> -                          bus->name);
>>> -            return NULL;
>>> -        } else {
>>> -            /* bus was not specified: try to find another one. */
>>> -            match = 0;
>>> -        }
>>> +        match = 0;
>>>       }
>>
>> This looks like the wrong fix to this problem -- if the user passed
>> us a specific name to search for and we found it and it was full, then
>> we definitely want to stop here. On the other hand, if the user passed
>> us a specific name and this bus isn't that named bus then we shouldn't
>> be checking the max_index at all.
>>
>> So I think the right fix is that the condition should be
>>    if (match && (bus_class->max_dev != 0)
>>        && (bus_class->max_dev <= bus->max_index)) {
>>
>> and the rest of the code in this function stays as is.
>>
>> -- PMM
>
> The final result looks the same no?
>
> If you look the qdev-monitor.c code just above the patch, you'll find the
> same thing:
>
>     if (name && (strcmp(bus->name, name) != 0)) {
>         match = 0;
>     }
>     if (bus_typename && !object_dynamic_cast(OBJECT(bus), bus_typename)) {
>
>         match = 0;
>     }
>     if ((bus_class->max_dev != 0) && (bus_class->max_dev <= bus->max_index))
> {
>         ...

You appear to be assuming this is an if..else if...else if
ladder -- it is not. Even if one of the first two if()s sets
match == 0, if we find the bus is at its max index we will
incorrectly go into the qerror_report case if name is not NULL.

(The other fix for this would be to change it to "if .. else if
.. else if", of course.)

-- PMM