Yang Hongyang <yan...@cn.fujitsu.com> writes:
> On 09/24/2015 03:43 PM, Markus Armbruster wrote:
>> This has finally reached the front of my review queue. I apologize for
>> the loooong delay.
>>
>> Copying Paolo for another pair of eyeballs (he wrote this code).
>>
> [...]
>>> +
>>> + opts = qemu_opts_find(qemu_find_opts_err("object", NULL), id);
>>> + qemu_opts_del(opts);
>>
>> qemu_find_opts_err("object", &error_abort) please, because when it
>> fails, we want to die right away, not when the null pointer it returns
>> gets dereferenced.
>
> Thanks for the review.
> Jason, do you want me to propose a fix on top of this series or simply drop
> this for now because this patch is an independent bug fix and won't affect the
> other filter patch series.
>
>>
>> Same sloppiness in netdev_del_completion() and qmp_netdev_del(), not
>> your patch's fault.
>>
>> Elsewhere, we store the QemuOpts in the object just so we can delete it:
>> DeviceState, DriveInfo. Paolo, what do you think?
>
> I don't get it. Currently, only objects created at the beginning through
> QEMU command line will be stored in the QemuOpts, objects that created
> with object_add won't stored in QemuOpts. Do you mean for DeviceState,
> DriveInfo they store there QemuOpts explicity so that they can delete it?
> Why don't we just delete it from objects directly instead?
Let me elaborate.
We have the same pattern in multiple places: some kind of object gets
configured via QemuOpts, and an object's QemuOpts need to stay around
until the object dies.
Example 1: Block device backends
DriveInfo has a member opts.
drive_new() stores the QemuOpts in dinfo->opts.
drive_info_del() destroys dinfo->opts.
Note: DriveInfo member opts is always non-null. But not every
BlockBackend has a DriveInfo.
Example 2: Device frontends
DeviceState has a member opts.
qdev_device_add() stores the QemuOpts in dev->opts.
device_finalize() destroys dev->opts.
Note: DeviceState member opts may be null (not every device is
created by qdev_device_add()). Fine, because qemu_opts_del(NULL) is
a no-op.
Example 3: Character device backends
CharDriverState has a member opts.
qemu_chr_new_from_opts() stores the QemuOpts in chr->opts.
qemu_chr_delete() destroys chr->opts.
Example 4: Network device backends
Two cases
A. netdev
qmp_netdev_add() does not store the QemuOpts.
qmp_netdev_del() still needs to destroy it. It has to find it
somehow. Here's how it does it:
opts = qemu_opts_find(qemu_find_opts_err("netdev", NULL), id);
if (!opts) {
error_setg(errp, "Device '%s' is not a netdev", id);
return;
}
The !opts condition is a non-obvious way to test "not created
with -netdev", see commit 645c949. Note that the commit's claim
that qemu_opts_del(NULL) crashes is no longer true since commit
4782183.
B. Legacy net
hmp_host_net_add() does not store the QemuOpts.
hmp_host_net_remove() still needs to destroy it. I can't see
where that happens, and I'm not sure it does.
Example 5: Generic object
object_create() does not store the QemuOpts.
It still needs to be destroyed along with the object. It isn't, and
your patch fixes it.
Personally, I find the technique in example 1-3 easier to understand
than the one in example 4-5.
