On 2025/08/07 03:04 PM, Amit Machhiwal wrote:

Hello,

On 2025/08/04 12:44 PM, Alex Mastro wrote:

quoted

Print the PCI device syspath to a vfio device's fdinfo. This enables tools
to query which device is associated with a given vfio device fd.

This results in output like below:

$ cat /proc/"$SOME_PID"/fdinfo/"$VFIO_FD" | grep vfio
vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0

Signed-off-by: Alex Mastro <redacted>

I tested this patch on a POWER9 bare metal system with a VFIO PCI device and
could see the VFIO device syspath in fdinfo.

 Without this patch:
 -------------------

    [root@localhost ~]# cat /proc/7059/fdinfo/188
    pos:    0
    flags:  02000002
    mnt_id: 17
    ino:    1113

 With this patch:
 ----------------
    [root@localhost ~]# cat /proc/7722/fdinfo/188
    pos:    0
    flags:  02000002
    mnt_id: 17
    ino:    2145
    vfio-device-syspath: /sys/devices/pci0031:00/0031:00:00.0/0031:01:00.0

..., and the code changes LGTM. Hence,

Additionally, I got a chance to test this patch on a pSeries POWER10 logical
partition (L1) running a KVM guest (L2) with a PCI device passthrough and I see
the expected results:

  [root@guest ~]# lscpu
  Architecture:             ppc64le
    Byte Order:             Little Endian
  CPU(s):                   20
    On-line CPU(s) list:    0-19
  Model name:               POWER10 (architected), altivec supported
    Model:                  2.0 (pvr 0080 0200)
  [...]

  [root@guest ~]# lspci
  [...]
  0001:00:01.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller PM9A1/PM9A3/980PRO

  root@host:~ # cat /proc/2116/fdinfo/68
  pos:    0
  flags:  02000002
  mnt_id: 17
  ino:    160
  vfio-device-syspath: /sys/devices/pci0182:70/0182:70:00.0

The L1 was booted with latest upstream kernel (HEAD: 53e760d89498) with the
patch applied and the L2 was booted on distro QEMU (version 10.0.2) and as well
as on latest upstream QEMU (HEAD: 5836af078321, version 10.0.93).

Thanks,
Amit

Reviewed-by: Amit Machhiwal <redacted>
Tested-by: Amit Machhiwal <redacted>

Thanks,
Amit

quoted

---
Changes in v4:
- Remove changes to vfio.h
- Link to v3: https://lore.kernel.org/r/20250801-show-fdinfo-v3-1-165dfcab89b9@fb.com (local)
Changes in v3:
- Remove changes to vfio_pci.c
- Add section to Documentation/filesystems/proc.rst
- Link to v2: https://lore.kernel.org/all/20250724-show-fdinfo-v2-1-2952115edc10@fb.com (local)
Changes in v2:
- Instead of PCI bdf, print the fully-qualified syspath (prefixed by
  /sys) to fdinfo.
- Rename the field to "vfio-device-syspath". The term "syspath" was
  chosen for consistency e.g. libudev's usage of the term.
- Link to v1: https://lore.kernel.org/r/20250623-vfio-fdinfo-v1-1-c9cec65a2922@fb.com (local)
---
 Documentation/filesystems/proc.rst | 14 ++++++++++++++
 drivers/vfio/vfio_main.c           | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2a17865dfe39..fc5ed3117834 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst

@@ -2162,6 +2162,20 @@ DMA Buffer files
 where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
 the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
 
+VFIO Device files
+~~~~~~~~~~~~~~~~
+
+::
+
+	pos:    0
+	flags:  02000002
+	mnt_id: 17
+	ino:    5122
+	vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0
+
+where 'vfio-device-syspath' is the sysfs path corresponding to the VFIO device
+file.
+
 3.9	/proc/<pid>/map_files - Information about memory mapped files
 ---------------------------------------------------------------------
 This directory contains symbolic links which represent memory mapped files

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 1fd261efc582..37a39cee10ed 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 +1355,22 @@ 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)
+{
+	char *path;
+	struct vfio_device_file *df = filep->private_data;
+	struct vfio_device *device = df->device;
+
+	path = kobject_get_path(&device->dev->kobj, GFP_KERNEL);
+	if (!path)
+		return;
+
+	seq_printf(m, "vfio-device-syspath: /sys%s\n", path);
+	kfree(path);
+}
+#endif
+
 const struct file_operations vfio_device_fops = {
 	.owner		= THIS_MODULE,
 	.open		= vfio_device_fops_cdev_open,

@@ -1363,6 +1380,9 @@ 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)

---
base-commit: 4518e5a60c7fbf0cdff393c2681db39d77b4f87e
change-id: 20250801-show-fdinfo-ef109ca738cf

Best regards,
-- 
Alex Mastro [off-list ref]