"Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
> * Eric Blake (ebl...@redhat.com) wrote:
>
>> -static void vmstate_save_old_style(QEMUFile *f, SaveStateEntry *se, QJSON
>> *vmdesc)
>> +static void vmstate_save_old_style(QEMUFile *f, SaveStateEntry *se,
>> + Visitor *vmdesc)
>> {
>> int64_t old_offset, size;
>> + const char *tmp;
>>
>> old_offset = qemu_ftell_fast(f);
>> se->ops->save_state(f, se->opaque);
>> size = qemu_ftell_fast(f) - old_offset;
>>
>> if (vmdesc) {
>> - json_prop_int(vmdesc, "size", size);
>> - json_start_array(vmdesc, "fields");
>> - json_start_object(vmdesc, NULL);
>> - json_prop_str(vmdesc, "name", "data");
>> - json_prop_int(vmdesc, "size", size);
>> - json_prop_str(vmdesc, "type", "buffer");
>> - json_end_object(vmdesc);
>> - json_end_array(vmdesc);
>> + visit_type_int(vmdesc, "size", &size, &error_abort);
>> + visit_start_list(vmdesc, "fields", NULL, 0, &error_abort);
>> + visit_start_struct(vmdesc, NULL, NULL, 0, &error_abort);
>
> Please avoid error_abort in migration code, especially on the source side.
> You've got an apparently happily working VM, we must never kill it
> while attempting migration.
These functions cannot fail, and &error_abort is a concise way to
express that. It's the same as
visit_type_int(vmdesc, "size", &size, &err);
assert(!err);
An alternative would be ignoring errors:
visit_type_int(vmdesc, "size", &size, NULL);
Ignoring violations of design invariants is hardly ever a good idea,
though.
Another alternative would be trying to recover from the violation, like
this:
visit_type_int(vmdesc, "size", &size, &err);
if (err) {
report we're fscked...
do whatever needs to be done to recover...
goto out;
}
Fancy untestable error paths are hardly ever good ideas, either.
Complete list of conditions where the JSON output visitor sets an error:
* Conditions where the visitor core sets an error:
- visit_type_uintN() when one of the visit_type_uint{8,16,32}() passes
a value out of bounds. This is a serious programming error in
qapi-visit-core.c. We're almost certainly screwed, and attempting
to continue is unsafe.
- visit_type_int(): likewise.
- output_type_enum() when the numeric value is out of bounds. This is
either a serious programming error in qapi-visit-core.c, or
corrupted state. Either way, we're almost certainly screwed, and
attempting to continue is unsafe.
- input_type_enum() when the string value is unknown. This is either
a serious programming error in qapi-visit-core.c, or bad input.
However, the JSON output visitor isn't supposed to ever call
input_type_enum(), so it's the former. Once again, we're almost
certainly screwed, and attempting to continue is unsafe.
* Conditions where the JSON output visitor itself sets an error:
- None.
Do you still object to &error_abort?
