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Re: [PATCH v12 12/19] multi-process: introduce proxy object


From: Marc-André Lureau
Subject: Re: [PATCH v12 12/19] multi-process: introduce proxy object
Date: Tue, 8 Dec 2020 16:23:25 +0400

Hi

On Wed, Dec 2, 2020 at 12:23 AM Jagannathan Raman <jag.raman@oracle.com> wrote:
From: Elena Ufimtseva <elena.ufimtseva@oracle.com>

Defines a PCI Device proxy object as a child of TYPE_PCI_DEVICE.

Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/hw/remote/proxy.h | 36 +++++++++++++++++
 hw/remote/proxy.c         | 98 +++++++++++++++++++++++++++++++++++++++++++++++
 MAINTAINERS               |  2 +
 hw/remote/meson.build     |  1 +
 4 files changed, 137 insertions(+)
 create mode 100644 include/hw/remote/proxy.h
 create mode 100644 hw/remote/proxy.c

diff --git a/include/hw/remote/proxy.h b/include/hw/remote/proxy.h
new file mode 100644
index 0000000..923432a
--- /dev/null
+++ b/include/hw/remote/proxy.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright © 2018, 2020 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef PROXY_H
+#define PROXY_H
+
+#include "hw/pci/pci.h"
+#include "io/channel.h"
+
+#define TYPE_PCI_PROXY_DEV "x-pci-proxy-dev"
+
+#define PCI_PROXY_DEV(obj) \
+            OBJECT_CHECK(PCIProxyDev, (obj), TYPE_PCI_PROXY_DEV)
+typedef struct PCIProxyDev PCIProxyDev;
+
+struct PCIProxyDev {
+    PCIDevice parent_dev;
+    char *fd;
+
+    /*
+     * Mutex used to protect the QIOChannel fd from
+     * the concurrent access by the VCPUs since proxy
+     * blocks while awaiting for the replies from the
+     * process remote.
+     */
+    QemuMutex io_mutex;
+    QIOChannel *ioc;
+    Error *migration_blocker;
+};
+
+#endif /* PROXY_H */
diff --git a/hw/remote/proxy.c b/hw/remote/proxy.c
new file mode 100644
index 0000000..29100bc
--- /dev/null
+++ b/hw/remote/proxy.c
@@ -0,0 +1,98 @@
+/*
+ * Copyright © 2018, 2020 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+
+#include "hw/remote/proxy.h"
+#include "hw/pci/pci.h"
+#include "qapi/error.h"
+#include "io/channel-util.h"
+#include "hw/qdev-properties.h"
+#include "monitor/monitor.h"
+#include "migration/blocker.h"
+
+static void proxy_set_socket(PCIProxyDev *pdev, int fd, Error **errp)
+{
+    pdev->ioc = qio_channel_new_fd(fd, errp);
+}

That one line function (called once) should be inlined.

+
+static Property proxy_properties[] = {
+    DEFINE_PROP_STRING("fd", PCIProxyDev, fd),
+    DEFINE_PROP_END_OF_LIST(),
+};
+

Generally we put properties just above class_init, where it is used.

+static void pci_proxy_dev_realize(PCIDevice *device, Error **errp)
+{

(errp shouldn't be NULL, but ERRP_GUARD would be safer)

+    PCIProxyDev *dev = PCI_PROXY_DEV(device);
+    int fd;
+
+    if (dev->fd) {
+        fd = monitor_fd_param(monitor_cur(), dev->fd, errp);
+        if (fd == -1) {
+            error_prepend(errp, "proxy: unable to parse fd: ");
+            return;
+        }
+        proxy_set_socket(dev, fd, errp);
+    } else {
+        error_setg(errp, "fd parameter not specified for %s",
+                   DEVICE(device)->id);
+        return;

We prefer early return, to keep the code easy to read.

if (!dev->fd) {
  return error...
}

the_normal_thing();
...

+    }
+
+    error_setg(&dev->migration_blocker, "%s does not support migration",
+               TYPE_PCI_PROXY_DEV);
+    if (migrate_add_blocker(dev->migration_blocker, errp)) {
+        error_free(dev->migration_blocker);

leave that free to dev_exit() ?
 
+        error_free(*errp);
+        dev->migration_blocker = NULL;
+        error_setg(errp, "Failed to set migration blocker");

Why not use the error from migrate_add_blocker?

+    }
+
+    qemu_mutex_init(&dev->io_mutex);
+    qio_channel_set_blocking(dev->ioc, true, NULL);
+}
+
+static void pci_proxy_dev_exit(PCIDevice *pdev)
+{
+    PCIProxyDev *dev = PCI_PROXY_DEV(pdev);
+
+    qio_channel_close(dev->ioc, NULL);

on early return in realize, dev->ioc is NULL. This will crash.


+
+    migrate_del_blocker(dev->migration_blocker);

So is migration_blocker, but this should be safe with NULL
 
+
+    error_free(dev->migration_blocker);
+}
+
+static void pci_proxy_dev_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
+
+    k->realize = pci_proxy_dev_realize;
+    k->exit = pci_proxy_dev_exit;
+    device_class_set_props(dc, proxy_properties);
+}
+
+static const TypeInfo pci_proxy_dev_type_info = {
+    .name          = TYPE_PCI_PROXY_DEV,
+    .parent        = TYPE_PCI_DEVICE,
+    .instance_size = sizeof(PCIProxyDev),
+    .class_init    = pci_proxy_dev_class_init,
+    .interfaces = (InterfaceInfo[]) {
+        { INTERFACE_CONVENTIONAL_PCI_DEVICE },
+        { },
+    },
+};
+
+static void pci_proxy_dev_register_types(void)
+{
+    type_register_static(&pci_proxy_dev_type_info);
+}
+
+type_init(pci_proxy_dev_register_types)
diff --git a/MAINTAINERS b/MAINTAINERS
index 24cb36e..ebd1d1d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3148,6 +3148,8 @@ F: include/hw/remote/remote-obj.h
 F: hw/remote/remote-obj.c
 F: include/hw/remote/memory.h
 F: hw/remote/memory.c
+F: hw/remote/proxy.c
+F: include/hw/remote/proxy.h

 Build and test automation
 -------------------------
diff --git a/hw/remote/meson.build b/hw/remote/meson.build
index 64da16c..569cd20 100644
--- a/hw/remote/meson.build
+++ b/hw/remote/meson.build
@@ -4,6 +4,7 @@ remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('machine.c'))
 remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('mpqemu-link.c'))
 remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('message.c'))
 remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('remote-obj.c'))
+remote_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('proxy.c'))

 specific_ss.add(when: 'CONFIG_MULTIPROCESS', if_true: files('memory.c'))

--
1.8.3.1



--
Marc-André Lureau

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