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Message-ID: <20250623-vfio-fdinfo-v1-1-c9cec65a2922@fb.com>
Date: Mon, 23 Jun 2025 14:02:38 -0700
From: Alex Mastro <amastro@...com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: <peterx@...hat.com>, <kbusch@...nel.org>, <kvm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Jason Gunthorpe <jgg@...pe.ca>,
Alex Mastro
<amastro@...com>
Subject: [PATCH] vfio/pci: print vfio-device name to fdinfo
Print the PCI device name to a vfio device's fdinfo. This enables tools
to query which device is associated with a given vfio device fd. It's
inspired by eventfd's printing of "eventfd-id" (fs/eventfd.c), which
lsof uses to format the NAME column (e.g. "[eventfd:7278]").
This results in output like below:
$ cat /proc/"$process_using_vfio"/fdinfo/"$vfio_device_fd" | grep vfio
vfio-device-name: 0000:c6:00.0
Signed-off-by: Alex Mastro <amastro@...com>
---
Hello, this is my first patch submission to vfio, and linux. We would
like our tools to be able to query the PCI device name for a given
vfio-device fd by inspecting a process's open file descriptors. It is
inspired by eventfd's id printing, which is nicely formatted by lsof in
the NAME column.
I am not sure to what extent this should be generalized, so I opted
to put as little policy as possible into vfio_main.c, and have each
vfio_device_fops implement what it means to show_fdinfo. The only
implementer is vfio_pci_ops in this change.
Alternatively, if we wanted to normalize show_fdinfo formatting, this
could instead hoist the print formatting up into vfio_main.c, and call
an optional vfio_device_ops->instance_name() to get the name. I opted
not to do this here due to unfamiliarity with other vfio drivers, but am
open to changing it.
I noticed that other vfio_device_fops are guarded by checks on
vfio_device_file.access_granted. From what I can tell, that shouldn't
be required here, since a vfio pci device is guaranteed to be
able to print its name (due to existence of vfio_device.pdev) after
vfio_device_ops.init() construction.
This change rooted on the for-linus branch of linux-vfio [1].
[1] https://github.com/awilliam/linux-vfio
---
drivers/vfio/pci/vfio_pci.c | 14 ++++++++++++++
drivers/vfio/vfio_main.c | 15 +++++++++++++++
include/linux/vfio.h | 2 ++
3 files changed, 31 insertions(+)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 5ba39f7623bb..b682766127ab 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -21,6 +21,7 @@
#include <linux/mutex.h>
#include <linux/notifier.h>
#include <linux/pm_runtime.h>
+#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/uaccess.h>
@@ -125,6 +126,16 @@ static int vfio_pci_open_device(struct vfio_device *core_vdev)
return 0;
}
+#ifdef CONFIG_PROC_FS
+static void vfio_pci_core_show_fdinfo(struct vfio_device *core_vdev, struct seq_file *m)
+{
+ struct vfio_pci_core_device *vdev =
+ container_of(core_vdev, struct vfio_pci_core_device, vdev);
+
+ seq_printf(m, "vfio-device-name: %s\n", pci_name(vdev->pdev));
+}
+#endif
+
static const struct vfio_device_ops vfio_pci_ops = {
.name = "vfio-pci",
.init = vfio_pci_core_init_dev,
@@ -138,6 +149,9 @@ static const struct vfio_device_ops vfio_pci_ops = {
.mmap = vfio_pci_core_mmap,
.request = vfio_pci_core_request,
.match = vfio_pci_core_match,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = vfio_pci_core_show_fdinfo,
+#endif
.bind_iommufd = vfio_iommufd_physical_bind,
.unbind_iommufd = vfio_iommufd_physical_unbind,
.attach_ioas = vfio_iommufd_physical_attach_ioas,
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 1fd261efc582..e02504247da8 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -28,6 +28,7 @@
#include <linux/pseudo_fs.h>
#include <linux/rwsem.h>
#include <linux/sched.h>
+#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/string.h>
@@ -1354,6 +1355,17 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
return device->ops->mmap(device, vma);
}
+#ifdef CONFIG_PROC_FS
+static void vfio_device_show_fdinfo(struct seq_file *m, struct file *filep)
+{
+ struct vfio_device_file *df = filep->private_data;
+ struct vfio_device *device = df->device;
+
+ if (device->ops->show_fdinfo)
+ device->ops->show_fdinfo(device, m);
+}
+#endif
+
const struct file_operations vfio_device_fops = {
.owner = THIS_MODULE,
.open = vfio_device_fops_cdev_open,
@@ -1363,6 +1375,9 @@ const struct file_operations vfio_device_fops = {
.unlocked_ioctl = vfio_device_fops_unl_ioctl,
.compat_ioctl = compat_ptr_ioctl,
.mmap = vfio_device_fops_mmap,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = vfio_device_show_fdinfo,
+#endif
};
static struct vfio_device *vfio_device_from_file(struct file *file)
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 707b00772ce1..54076045a44f 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -16,6 +16,7 @@
#include <linux/cdev.h>
#include <uapi/linux/vfio.h>
#include <linux/iova_bitmap.h>
+#include <linux/seq_file.h>
struct kvm;
struct iommufd_ctx;
@@ -135,6 +136,7 @@ struct vfio_device_ops {
void (*dma_unmap)(struct vfio_device *vdev, u64 iova, u64 length);
int (*device_feature)(struct vfio_device *device, u32 flags,
void __user *arg, size_t argsz);
+ void (*show_fdinfo)(struct vfio_device *device, struct seq_file *m);
};
#if IS_ENABLED(CONFIG_IOMMUFD)
---
base-commit: c1d9dac0db168198b6f63f460665256dedad9b6e
change-id: 20250623-vfio-fdinfo-767e75a1496a
Best regards,
--
Alex Mastro <amastro@...com>
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