[PATCH 6/8] selftests/vfio: Add vfio_pci_irq_reenable() helper

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

Selftest drivers that recover from a fault by issuing VFIO_DEVICE_RESET
need to re-arm device interrupts afterwards.  VFIO_DEVICE_RESET tears
down the kernel-side IRQ trigger so a subsequent VFIO_DEVICE_SET_IRQS
is required, but the user-side eventfds (and any fd cached in a test
fixture) are still valid and must be preserved.

vfio_pci_irq_enable() refuses to be called for vectors that already
have an eventfd (VFIO_ASSERT_LT), and vfio_pci_irq_disable() closes
all eventfds before resetting the trigger, so neither is suitable.

Add vfio_pci_irq_reenable(device, index, vector, count) which asserts
that the requested range has existing eventfds and re-issues
VFIO_DEVICE_SET_IRQS using them.  Signature mirrors vfio_pci_irq_enable().

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
---
 .../lib/include/libvfio/vfio_pci_device.h     |  2 ++
 .../selftests/vfio/lib/vfio_pci_device.c      | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
index 2858885a89bb..a362e2b2bfda 100644
--- a/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
+++ b/tools/testing/selftests/vfio/lib/include/libvfio/vfio_pci_device.h
@@ -68,6 +68,8 @@ void vfio_pci_config_access(struct vfio_pci_device *device, bool write,
 void vfio_pci_irq_enable(struct vfio_pci_device *device, u32 index,
 			 u32 vector, int count);
 void vfio_pci_irq_disable(struct vfio_pci_device *device, u32 index);
+void vfio_pci_irq_reenable(struct vfio_pci_device *device, u32 index,
+			   u32 vector, int count);
 void vfio_pci_irq_trigger(struct vfio_pci_device *device, u32 index, u32 vector);
 
 static inline void fcntl_set_nonblock(int fd)
diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index fc75e04ef010..7b8394d0ac50 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -106,6 +106,28 @@ void vfio_pci_irq_disable(struct vfio_pci_device *device, u32 index)
 	vfio_pci_irq_set(device, index, 0, 0, NULL);
 }
 
+/*
+ * Re-issue VFIO_DEVICE_SET_IRQS for an already-enabled vector range using
+ * the existing eventfds.  Intended for drivers that need to re-arm device
+ * interrupts after a VFIO_DEVICE_RESET, which tears down the kernel-side
+ * IRQ trigger but leaves user-side eventfds intact.  Recreating the
+ * eventfds would invalidate any test-fixture cache of the fd, so this
+ * helper deliberately preserves them.
+ */
+void vfio_pci_irq_reenable(struct vfio_pci_device *device, u32 index,
+			   u32 vector, int count)
+{
+	int i;
+
+	check_supported_irq_index(index);
+
+	for (i = vector; i < vector + count; i++)
+		VFIO_ASSERT_GE(device->msi_eventfds[i], 0,
+			       "vector %d eventfd not allocated\n", i);
+
+	vfio_pci_irq_set(device, index, vector, count, device->msi_eventfds + vector);
+}
+
 static void vfio_pci_irq_get(struct vfio_pci_device *device, u32 index,
 			     struct vfio_irq_info *irq_info)
 {
-- 
2.51.0