Re: [PATCH qemu-kvm] device-assignment: add config fd qdev property

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2010-05-19 at 12:00 -0700, Chris Wright wrote:
> When libvirt launches a guest it first chowns the relevenat
> /sys/bus/pci/.../config file for an assigned device then drops privileges.
> 
> This causes an issue for device assignment because despite being file
> owner, the sysfs config space file checks for CAP_SYS_ADMIN before
> allowing access to device dependent config space.
> 
> This adds a new qdev configfd property which allows libvirt to open the
> sysfs config space file and give qemu an already opened file descriptor.
> Along with a change pending for the 2.6.35 kernel, this allows the
> capability check to compare against privileges from when the file was
> opened.

We need to make configfd be a string option so that we can pass a
descriptor from libvirt for the hotplug case.  Here's a rework.

Signed-off-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index eb31c78..3c5184f 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -37,6 +37,7 @@
 #include "console.h"
 #include "device-assignment.h"
 #include "loader.h"
+#include "monitor.h"
 #include <pci/pci.h>
 
 /* From linux/ioport.h */
@@ -612,14 +613,28 @@ static int get_real_device(AssignedDevice *pci_dev, uint16_t r_seg,
 
     snprintf(name, sizeof(name), "%sconfig", dir);
 
-    fd = open(name, O_RDWR);
-    if (fd == -1) {
-        fprintf(stderr, "%s: %s: %m\n", __func__, name);
-        return 1;
+    if (pci_dev->configfd_name && *pci_dev->configfd_name) {
+        if (qemu_isdigit(pci_dev->configfd_name[0])) {
+            dev->config_fd = strtol(pci_dev->configfd_name, NULL, 0);
+        } else {
+            dev->config_fd = monitor_get_fd(cur_mon, pci_dev->configfd_name);
+            if (dev->config_fd < 0) {
+                fprintf(stderr, "%s: (%s) unkown\n", __func__,
+                        pci_dev->configfd_name);
+                return 1;
+            }
+        }
+    } else {
+        dev->config_fd = open(name, O_RDWR);
+
+        if (dev->config_fd == -1) {
+            fprintf(stderr, "%s: %s: %m\n", __func__, name);
+            return 1;
+        }
     }
-    dev->config_fd = fd;
 again:
-    r = read(fd, pci_dev->dev.config, pci_config_size(&pci_dev->dev));
+    r = read(dev->config_fd, pci_dev->dev.config,
+             pci_config_size(&pci_dev->dev));
     if (r < 0) {
         if (errno == EINTR || errno == EAGAIN)
             goto again;
@@ -1433,6 +1448,7 @@ static PCIDeviceInfo assign_info = {
     .qdev.props   = (Property[]) {
         DEFINE_PROP("host", AssignedDevice, host, qdev_prop_hostaddr, PCIHostDevice),
         DEFINE_PROP_UINT32("iommu", AssignedDevice, use_iommu, 1),
+        DEFINE_PROP_STRING("configfd", AssignedDevice, configfd_name),
         DEFINE_PROP_END_OF_LIST(),
     },
 };
diff --git a/hw/device-assignment.h b/hw/device-assignment.h
index d561112..f70ace9 100644
--- a/hw/device-assignment.h
+++ b/hw/device-assignment.h
@@ -104,6 +104,7 @@ typedef struct AssignedDevice {
     target_phys_addr_t msix_table_addr;
     int mmio_index;
     int need_emulate_cmd;
+    char *configfd_name;
     QLIST_ENTRY(AssignedDevice) next;
 } AssignedDevice;