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Message-ID: <20250814141153.8294c6d3-83-amachhiw@linux.ibm.com>
Date: Thu, 14 Aug 2025 14:28:16 +0530
From: Amit Machhiwal <amachhiw@...ux.ibm.com>
To: Alex Mastro <amastro@...com>, Alex Williamson <alex.williamson@...hat.com>,
Jonathan Corbet <corbet@....net>, Jason Gunthorpe <jgg@...pe.ca>,
Keith Busch <kbusch@...nel.org>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
kvm@...r.kernel.org
Subject: Re: [PATCH v4] vfio/pci: print vfio-device syspath to fdinfo
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@...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@...alhost ~]# cat /proc/7059/fdinfo/188
> pos: 0
> flags: 02000002
> mnt_id: 17
> ino: 1113
>
> With this patch:
> ----------------
> [root@...alhost ~]# 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@...st ~]# 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@...st ~]# lspci
[...]
0001:00:01.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller PM9A1/PM9A3/980PRO
root@...t:~ # 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@...ux.ibm.com>
> Tested-by: Amit Machhiwal <amachhiw@...ux.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@...com>
> >
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