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

[PATCH v4] 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 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>

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

[Amit Machhiwal]

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.

 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>
> 

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

[Alex Mastro]

On Thu, Aug 07, 2025 at 03:04:29PM +0530, Amit Machhiwal wrote:
> Reviewed-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> Tested-by: Amit Machhiwal <amachhiw@linux.ibm.com>

Hi Amit, thanks for taking the time to test and review!

Alex

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

[Cédric Le Goater]

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 ?
Are you using an upstream QEMU to test too ?

and which device ?

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>
>>
> 

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

[Amit Machhiwal]

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>
> > > 
> > 
> 

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

[Cédric Le Goater]

On 8/8/25 17:45, Amit Machhiwal wrote:
> 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.

It is good to know that device pass-through still works with upstream on
OpenPower servers.

Have you tried VFs ?

Thanks Amit,

C.

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

[Amit Machhiwal]

On 2025/08/08 06:44 PM, Cédric Le Goater wrote:
> On 8/8/25 17:45, Amit Machhiwal wrote:
> > 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.
> 
> It is good to know that device pass-through still works with upstream on
> OpenPower servers.
> 
> Have you tried VFs ?

I didn't get a chance to try VFs yet, Cédric.

> 
> Thanks Amit,

No problem. :)

Thanks,
Amit

> 
> C.
> 

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

[Amit Machhiwal]

On 2025/08/07 03:04 PM, 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.
> 
>  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 <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>
> > 

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

[Alex Williamson]

On Mon, 4 Aug 2025 12:44:31 -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 v4:
> - Remove changes to vfio.h
> - Link to v3: https://lore.kernel.org/r/20250801-show-fdinfo-v3-1-165dfcab89b9@fb.com

Applied to vfio next branch for v6.18.  Thanks,

Alex