Re: [PATCH v4] vfio/pci: print vfio-device syspath to fdinfo

[Amit Machhiwal <amachhiw@linux.ibm.com>]

Hi Cédric,

Please find my comments inline:

On 2025/08/08 03:49 PM, Cédric Le Goater wrote:
> Hello Amit,
> 
> On 8/7/25 11:34, Amit Machhiwal wrote:
> > Hello,
> > 
> > On 2025/08/04 12:44 PM, Alex Mastro 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>
> > 
> > I tested this patch on a POWER9 bare metal system with a VFIO PCI device and
> > could see the VFIO device syspath in fdinfo.
> 
> POWER9 running on OPAL FW : I am curious about the software stack.
> 
> I suppose this is the latest upstream kernel ?

Yes, I used the latest upstream kernel and applied this patch on top of commit
cca7a0aae895.

> Are you using an upstream QEMU to test too ?

No, I had used the Fedora 42 distro qemu. The version details are as below:

  [root@localhost ~]# qemu-system-ppc64 --version
  QEMU emulator version 9.2.4 (qemu-9.2.4-1.fc42)
  Copyright (c) 2003-2024 Fabrice Bellard and the QEMU Project developers

I gave the upstream qemu (HEAD pointing to cd21ee5b27) a try and I see the same
behavior with that too.

  [root@localhost ~]# ./qemu-system-ppc64 --version
  QEMU emulator version 10.0.92 (v10.1.0-rc2-4-gcd21ee5b27-dirty)
  Copyright (c) 2003-2025 Fabrice Bellard and the QEMU Project developers

  [root@localhost ~]# cat /proc/52807/fdinfo/191
  pos:    0
  flags:  02000002
  mnt_id: 17
  ino:    1125
  vfio-device-syspath: /sys/devices/pci0031:00/0031:00:00.0/0031:01:00.0

> 
> and which device ?

I'm using a Broadcom NetXtreme network card (4-port) and passing through its
fn0.

  [root@guest ~]# lspci
  [...]
  0001:00:01.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev 01)

Please let me know if I may help you with any additional information.

Thanks,
Amit

> 
> Thanks,
> 
> C.
> 
> 
> 
> 
> > 
> >   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,
> > 
> > Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> > Tested-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> > 
> > Thanks,
> > Amit
> > 
> > > ---
> > > Changes in v4:
> > > - Remove changes to vfio.h
> > > - Link to v3: https://lore.kernel.org/r/20250801-show-fdinfo-v3-1-165dfcab89b9@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 ++++++++++++++++++++
> > >   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 <amastro@fb.com>
> > > 
> > 
>