[PATCH v2 2/2] pci-assign: Fix MSI-X capability test

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

Commit c4525754 added a capability check for KVM_CAP_DEVICE_MSIX,
which is unfortunately not exposed, resulting in MSIX never
being listed as a capability.  This breaks anything depending on
MSIX, such as igbvf.  Instead let's use a dummy call to
KVM_ASSIGN_SET_MSIX_NR which will return -EFAULT if the call
exists.

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

 hw/device-assignment.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 137c409..f0a6ca9 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1212,7 +1212,10 @@ static int assigned_device_pci_cap_init(PCIDevice *pci_dev)
     }
     /* Expose MSI-X capability */
     pos = pci_find_cap_offset(pci_dev, PCI_CAP_ID_MSIX, 0);
-    if (pos != 0 && kvm_check_extension(kvm_state, KVM_CAP_DEVICE_MSIX)) {
+    /* Would really like to test kvm_check_extension(, KVM_CAP_DEVICE_MSIX),
+     * but the kernel doesn't expose it.  Instead do a dummy call to
+     * KVM_ASSIGN_SET_MSIX_NR to see if it exists. */
+    if (pos != 0 && kvm_assign_set_msix_nr(kvm_state, NULL) == -EFAULT) {
         int bar_nr;
         uint32_t msix_table_entry;