Re: [PATCH v9 10/17] vfio-user: run vfio-user context

[Markus Armbruster <armbru@redhat.com>]

Jag Raman <jag.raman@oracle.com> writes:

>> On May 4, 2022, at 7:42 AM, Markus Armbruster <armbru@redhat.com> wrote:
>> 
>> Jagannathan Raman <jag.raman@oracle.com> writes:
>> 
>>> Setup a handler to run vfio-user context. The context is driven by
>>> messages to the file descriptor associated with it - get the fd for
>>> the context and hook up the handler with it
>>> 
>>> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
>>> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
>>> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
>>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> ---
>>> qapi/misc.json | 30 +++++++++++
>>> hw/remote/vfio-user-obj.c | 102 +++++++++++++++++++++++++++++++++++++-
>>> 2 files changed, 131 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/qapi/misc.json b/qapi/misc.json
>>> index b83cc39029..fa49f2876a 100644
>>> --- a/qapi/misc.json
>>> +++ b/qapi/misc.json
>>> @@ -553,3 +553,33 @@
>>> ##
>>> { 'event': 'RTC_CHANGE',
>>> 'data': { 'offset': 'int', 'qom-path': 'str' } }
>>> +
>>> +##
>>> +# @VFU_CLIENT_HANGUP:
>>> +#
>>> +# Emitted when the client of a TYPE_VFIO_USER_SERVER closes the
>>> +# communication channel
>>> +#
>>> +# @vfu-id: ID of the TYPE_VFIO_USER_SERVER object
>>> +#
>>> +# @vfu-qom-path: path to the TYPE_VFIO_USER_SERVER object in the QOM tree
>>> +#
>>> +# @dev-id: ID of attached PCI device
>>> +#
>>> +# @dev-qom-path: path to attached PCI device in the QOM tree
>> 
>> I'm still unsure what kind(s) of ID @vfu-id and @dev-id are. See below.
>
> I’m not sure what you mean by kind of ID - I thought of ID as a
> unique string. I’ll try my best to explain.

Okay, let me try to clarify.

We have many, many ID namespaces, each associated with a certain kind of
object: device IDs for TYPE_DEVICE, object IDs for TYPE_OBJECT
implementing TYPE_USER_CREATABLE), block backend node names for
BlockDriverState, ...

Aside: I believe a single namespace would have been a wiser design
choice, but that ship sailed long ago.

To which of these namespaces do these two IDs belong, respectively?

> dev-id and vfu-id are the “id" sub-options of “-device” and “-object” command-line
> options respectively.

This answers my question.

> "dev-id” is the “id” member of “DeviceState” which QEMU sets using
> qdev_set_id() when the device is added. 
>
> The Object ID (vfu-id in this case) is a bit tricky. It’s also the “id”
> command-line sub-option, but QEMU stores it as a child property
> of the parent object.
>
>> 
>>> +#
>>> +# Since: 7.1
>>> +#
>>> +# Example:
>>> +#
>>> +# <- { "event": "VFU_CLIENT_HANGUP",
>>> +# "data": { "vfu-id": "vfu1",
>>> +# "vfu-qom-path": "/objects/vfu1",
>>> +# "dev-id": "sas1",
>>> +# "dev-qom-path": "/machine/peripheral/sas1" },
>>> +# "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
>>> +#
>>> +##
>>> +{ 'event': 'VFU_CLIENT_HANGUP',
>>> + 'data': { 'vfu-id': 'str', 'vfu-qom-path': 'str',
>>> + 'dev-id': 'str', 'dev-qom-path': 'str' } }
>>> diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
>>> index 3ca6aa2b45..3a4c6a9fa0 100644
>>> --- a/hw/remote/vfio-user-obj.c
>>> +++ b/hw/remote/vfio-user-obj.c
>>> @@ -27,6 +27,9 @@
>>> *
>>> * device - id of a device on the server, a required option. PCI devices
>>> * alone are supported presently.
>>> + *
>>> + * notes - x-vfio-user-server could block IO and monitor during the
>>> + * initialization phase.
>>> */
>>> 
>>> #include "qemu/osdep.h"
>>> @@ -40,11 +43,14 @@
>>> #include "hw/remote/machine.h"
>>> #include "qapi/error.h"
>>> #include "qapi/qapi-visit-sockets.h"
>>> +#include "qapi/qapi-events-misc.h"
>>> #include "qemu/notify.h"
>>> +#include "qemu/thread.h"
>>> #include "sysemu/sysemu.h"
>>> #include "libvfio-user.h"
>>> #include "hw/qdev-core.h"
>>> #include "hw/pci/pci.h"
>>> +#include "qemu/timer.h"
>>> 
>>> #define TYPE_VFU_OBJECT "x-vfio-user-server"
>>> OBJECT_DECLARE_TYPE(VfuObject, VfuObjectClass, VFU_OBJECT)
>>> @@ -86,6 +92,8 @@ struct VfuObject {
>>> PCIDevice *pci_dev;
>>> 
>>> Error *unplug_blocker;
>>> +
>>> + int vfu_poll_fd;
>>> };
>>> 
>>> static void vfu_object_init_ctx(VfuObject *o, Error **errp);
>>> @@ -164,6 +172,76 @@ static void vfu_object_set_device(Object *obj, const char *str, Error **errp)
>>> vfu_object_init_ctx(o, errp);
>>> }
>>> 
>>> +static void vfu_object_ctx_run(void *opaque)
>>> +{
>>> + VfuObject *o = opaque;
>>> + const char *vfu_id;
>>> + char *vfu_path, *pci_dev_path;
>>> + int ret = -1;
>>> +
>>> + while (ret != 0) {
>>> + ret = vfu_run_ctx(o->vfu_ctx);
>>> + if (ret < 0) {
>>> + if (errno == EINTR) {
>>> + continue;
>>> + } else if (errno == ENOTCONN) {
>>> + vfu_id = object_get_canonical_path_component(OBJECT(o));
>>> + vfu_path = object_get_canonical_path(OBJECT(o));
>> 
>> Hmm. @vfu_id is always the last component of @vfu_path. Why do we need
>> to send both?
>
> vfu_id is the ID that the user/Orchestrator passed as a command-line option
> during addition/creation. So it made sense to report back with the same ID
> that they used. But I’m OK with dropping this if that’s what you prefer.

Matter of taste, I guess.  I'd drop it simply to saves us the trouble of
documenting it.

If we decide to keep it, then I think we should document it's always the
last component of @vfu_path.

>>> + g_assert(o->pci_dev);
>>> + pci_dev_path = object_get_canonical_path(OBJECT(o->pci_dev));
>>> + qapi_event_send_vfu_client_hangup(vfu_id, vfu_path,
>>> + o->device, pci_dev_path);
>> 
>> Where is o->device set? I'm asking because I it must not be null here,
>> and that's not locally obvious.
>
> Yeah, it’s not obvious from this patch that o->device is guaranteed to be
> non-NULL. It’s set by vfu_object_set_device(). Please see the following
> patches in the series:
> vfio-user: define vfio-user-server object
> vfio-user: instantiate vfio-user context

vfu_object_set_device() is a QOM property setter.  It gets called if and
only if the property is set.  If it's never set, ->device remains null.
What ensures it's always set?

> There’s already an assert for o->pci_dev here, but we could add one
> for o->device too?

I'll make up my mind when I'm convinced o->device can't be null here.

> Thank you!

You're welcome!