[PATCH v3] vfio/pci: print vfio-device syspath to fdinfo

[PATCH v3] vfio/pci: print vfio-device syspath to fdinfo

[Alex Mastro]

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 <amastro@fb.com>
---
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
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
---
 Documentation/filesystems/proc.rst | 14 ++++++++++++++
 drivers/vfio/vfio_main.c           | 20 ++++++++++++++++++++
 include/linux/vfio.h               |  2 ++
 3 files changed, 36 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)
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: 4518e5a60c7fbf0cdff393c2681db39d77b4f87e
change-id: 20250801-show-fdinfo-ef109ca738cf

Best regards,
-- 
Alex Mastro <amastro@fb.com>

Re: [PATCH v3] vfio/pci: print vfio-device syspath to fdinfo

[Alex Williamson]

On Fri, 1 Aug 2025 13:50:56 -0700
Alex Mastro <amastro@fb.com> wrote:

> 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 <amastro@fb.com>
> ---
> 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
> 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
> ---
>  Documentation/filesystems/proc.rst | 14 ++++++++++++++
>  drivers/vfio/vfio_main.c           | 20 ++++++++++++++++++++
>  include/linux/vfio.h               |  2 ++
>  3 files changed, 36 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)
> 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);
>  };

Changes in this file look spurious, vfio_device_ops vs
vfio_device_fops?  Nothing implements or consumes the vfio_device_ops
callback here.  Thanks,

Alex

Re: [PATCH v3] vfio/pci: print vfio-device syspath to fdinfo

[Alex Mastro]

On Mon, Aug 04, 2025 at 10:25:59AM -0600, Alex Williamson wrote:
> Changes in this file look spurious, vfio_device_ops vs
> vfio_device_fops?  Nothing implements or consumes the vfio_device_ops
> callback here.

Agh. Yes. I missed removing this. Fixing in v4.