[PATCH v3 1/8] vfio: add helper to find PCI device by vendor/device ID

[Jose Ignacio Tornos Martinez <jtornosm@redhat.com>]

Add vfio_file_find_pci_device() that searches for a PCI device with
the specified vendor/device ID within a VFIO group or device file. The
function walks the group device list to find a matching PCI device, or
checks the single device for a cdev-based file.

This helper enables other subsystems (e.g. KVM PCI MSI domain) to
locate VFIO-owned PCI devices by their IDs without depending on VFIO
internals. The companion vfio_file_device() provides access to the
underlying vfio_device from a device file descriptor.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
---
v3: new
v2: https://lore.kernel.org/all/20261011074514.515894-1-jtornosm@redhat.com/

 drivers/vfio/group.c     | 41 ++++++++++++++++++++++++++++++++++++++++
 drivers/vfio/vfio_main.c |  6 ++++++
 include/linux/vfio.h     | 10 ++++++++++
 3 files changed, 57 insertions(+)

diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 185f359f75d3..0b6cf90edda3 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -10,6 +10,7 @@
  * Author: Tom Lyon, pugs@cisco.com
  */
 
+#include <linux/pci.h>
 #include <linux/vfio.h>
 #include <linux/iommufd.h>
 #include <linux/anon_inodes.h>
@@ -894,6 +895,46 @@ bool vfio_file_has_dev(struct file *file, struct vfio_device *device)
 }
 EXPORT_SYMBOL_GPL(vfio_file_has_dev);
 
+struct vfio_device *vfio_file_find_pci_device(struct file *file,
+					      u16 vendor, u16 device_id)
+{
+	struct vfio_group *group;
+	struct vfio_device *vdev;
+	struct vfio_device *ret = NULL;
+
+	group = vfio_group_from_file(file);
+	if (group) {
+		mutex_lock(&group->device_lock);
+		list_for_each_entry(vdev, &group->device_list, group_next) {
+			struct pci_dev *pdev;
+
+			if (!dev_is_pci(vdev->dev))
+				continue;
+
+			pdev = to_pci_dev(vdev->dev);
+			if (pdev->vendor == vendor &&
+			    pdev->device == device_id) {
+				ret = vdev;
+				break;
+			}
+		}
+		mutex_unlock(&group->device_lock);
+		return ret;
+	}
+
+	vdev = vfio_file_device(file);
+	if (vdev && dev_is_pci(vdev->dev)) {
+		struct pci_dev *pdev = to_pci_dev(vdev->dev);
+
+		if (pdev->vendor == vendor &&
+		    pdev->device == device_id)
+			return vdev;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(vfio_file_find_pci_device);
+
 static char *vfio_devnode(const struct device *dev, umode_t *mode)
 {
 	return kasprintf(GFP_KERNEL, "vfio/%s", dev_name(dev));
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 4e5d738ccf4b..a83e5d805eac 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -1551,6 +1551,12 @@ void vfio_file_set_kvm(struct file *vfio_file, struct file *kvm)
 }
 EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
 
+struct vfio_device *vfio_file_device(struct file *file)
+{
+	return vfio_device_from_file(file);
+}
+EXPORT_SYMBOL_GPL(vfio_file_device);
+
 /*
  * Sub-module support
  */
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 0cc91c6f96d2..a62fbf42458a 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -364,6 +364,8 @@ struct iommu_group *vfio_file_iommu_group(struct file *file);
 #if IS_ENABLED(CONFIG_VFIO_GROUP)
 bool vfio_file_is_group(struct file *file);
 bool vfio_file_has_dev(struct file *file, struct vfio_device *device);
+struct vfio_device *vfio_file_find_pci_device(struct file *file,
+					      u16 vendor, u16 device_id);
 #else
 static inline bool vfio_file_is_group(struct file *file)
 {
@@ -374,10 +376,18 @@ static inline bool vfio_file_has_dev(struct file *file, struct vfio_device *devi
 {
 	return false;
 }
+
+static inline struct vfio_device *vfio_file_find_pci_device(struct file *file,
+							    u16 vendor,
+							    u16 device_id)
+{
+	return NULL;
+}
 #endif
 bool vfio_file_is_valid(struct file *file);
 bool vfio_file_enforced_coherent(struct file *file);
 void vfio_file_set_kvm(struct file *vfio_file, struct file *kvm);
+struct vfio_device *vfio_file_device(struct file *file);
 
 #define VFIO_PIN_PAGES_MAX_ENTRIES	(PAGE_SIZE/sizeof(unsigned long))
 
-- 
2.56.0