9:37 a.m.
Am 27.09.2021 um 13:39 hat Kevin Wolf geschrieben:
Am 27.09.2021 um 13:06 hat Damien Hedde geschrieben:
> On 9/24/21 11:04, Kevin Wolf wrote:
> > Directly call qdev_device_add_from_qdict() for QMP device_add instead of
> > first going through QemuOpts and converting back to QDict.
> >
> > Note that this changes the behaviour of device_add, though in ways that
> > should be considered bug fixes:
> >
> > QemuOpts ignores differences between data types, so you could
> > successfully pass a string "123" for an integer property, or a
string
> > "on" for a boolean property (and vice versa). After this change,
the
> > correct data type for the property must be used in the JSON input.
> >
> > qemu_opts_from_qdict() also silently ignores any options whose value is
> > a QDict, QList or QNull.
> >
> > To illustrate, the following QMP command was accepted before and is now
> > rejected for both reasons:
> >
> > { "execute": "device_add",
> > "arguments": { "driver": "scsi-cd",
> > "drive": { "completely":
"invalid" },
> > "physical_block_size": "4096" } }
> >
> > Signed-off-by: Kevin Wolf <kwolf(a)redhat.com>
> > ---
> > softmmu/qdev-monitor.c | 18 +++++++++++-------
> > 1 file changed, 11 insertions(+), 7 deletions(-)
> >
> > diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> > index c09b7430eb..8622ccade6 100644
> > --- a/softmmu/qdev-monitor.c
> > +++ b/softmmu/qdev-monitor.c
> > @@ -812,7 +812,8 @@ void hmp_info_qdm(Monitor *mon, const QDict *qdict)
> > qdev_print_devinfos(true);
> > }
> > -void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
> > +static void monitor_device_add(QDict *qdict, QObject **ret_data,
> > + bool from_json, Error **errp)
> > {
> > QemuOpts *opts;
> > DeviceState *dev;
> > @@ -825,7 +826,9 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error
**errp)
> > qemu_opts_del(opts);
> > return;
> > }
> > - dev = qdev_device_add(opts, errp);
> > + qemu_opts_del(opts);
> > +
> > + dev = qdev_device_add_from_qdict(qdict, from_json, errp);
>
> Hi Kevin,
>
> I'm wandering if deleting the opts (which remove it from the "device"
opts
> list) is really a no-op ?
It's not exactly a no-op. Previously, the QemuOpts would only be freed
when the device is destroying, now we delete it immediately after
creating the device. This could matter in some cases.
The one case I was aware of is that QemuOpts used to be responsible for
checking for duplicate IDs. Obviously, it can't do this job any more
when we call qemu_opts_del() right after creating the device. This is
the reason for patch 6.
> The opts list is, eg, traversed in hw/net/virtio-net.c in the function
> failover_find_primary_device_id() which may be called during the
> virtio_net_set_features() (a TYPE_VIRTIO_NET method).
> I do not have the knowledge to tell when this method is called. But If this
> is after we create the devices. Then the list will be empty at this point
> now.
>
> It seems, there are 2 other calling sites of
> "qemu_opts_foreach(qemu_find_opts("device"), [...]" in
net/vhost-user.c and
> net/vhost-vdpa.c
Yes, you are right. These callers probably need to be changed. Going
through the command line options rather than looking at the actual
device objects that exist doesn't feel entirely clean anyway.
So I tried to have a look at the virtio-net case, and ended up very
confused.
Obviously looking at command line options (even of a differrent device)
from within a device is very unclean. With a non-broken, i.e. type safe,
device-add (as well as with the JSON CLI option introduced by this
series), we can't have a QemuOpts any more that is by definition unsafe.
So this code needs a replacement.
My naive idea was that we just need to look at runtime state instead.
Don't search the options for a device with a matching 'failover_pair_id'
(which, by the way, would fail as soon as any other device introduces a
property with the same name), but search for actual PCIDevices in qdev
that have pci_dev->failover_pair_id set accordingly.
However, the logic in failover_add_primary() suggests that we can have a
state where QemuOpts for a device exist, but the device doesn't, and
then it hotplugs the device from the command line options. How would we
ever get into such an inconsistent state where QemuOpts contains a
device that doesn't exist? Normally devices get their QemuOpts when they
are created and device_finalize() deletes the QemuOpts again.
Any suggestions how to get rid of the QemuOpts abuse in the failover
code?
If this is a device that we previously managed to rip out without
deleting its QemuOpts, can we store its dev->opts (which is a type safe
QDict after this series) somewhere locally instead of looking at global
state? Preferably I would even like to get rid of dev->opts because we
really should look at live state rather than command line options after
device creation, but I guess one step at a time.
(Actually, I'm half tempted to just break it because no test cases seem
to exist, so apparently nobody is really interested in it.)
Kevin