linux-kernel - Re: [PATCH] vfio: Dump migration features under debugfs

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Message-ID: <20251006134642.4aee649a.alex.williamson@redhat.com>
Date: Mon, 6 Oct 2025 13:46:42 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Cédric Le Goater <clg@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio: Dump migration features under debugfs

On Thu, 18 Sep 2025 14:19:28 +0200
Cédric Le Goater <clg@...hat.com> wrote:

> A debugfs directory was recently added for VFIO devices. Add a new
> "features" file under the migration sub-directory to expose which
> features the device supports.
> 
> Signed-off-by: Cédric Le Goater <clg@...hat.com>
> ---
>  drivers/vfio/debugfs.c                 | 19 +++++++++++++++++++
>  Documentation/ABI/testing/debugfs-vfio |  6 ++++++
>  2 files changed, 25 insertions(+)

I think this was overlooked, but should have been considered for the
v6.18 merge window.  Given the plan to get the DMA mapping
optimizations in this merge window, I think we should pull this in too.
Applied to the vfio next branch.  Thanks,

Alex
 
> diff --git a/drivers/vfio/debugfs.c b/drivers/vfio/debugfs.c
> index 298bd866f15766b50e342511d8a83f0621cb4f55..8b0ca7a09064072b3d489dab8072dbb1a2871d10 100644
> --- a/drivers/vfio/debugfs.c
> +++ b/drivers/vfio/debugfs.c
> @@ -58,6 +58,23 @@ static int vfio_device_state_read(struct seq_file *seq, void *data)
>  	return 0;
>  }
>  
> +static int vfio_device_features_read(struct seq_file *seq, void *data)
> +{
> +	struct device *vf_dev = seq->private;
> +	struct vfio_device *vdev = container_of(vf_dev, struct vfio_device, device);
> +
> +	if (vdev->migration_flags & VFIO_MIGRATION_STOP_COPY)
> +		seq_puts(seq, "stop-copy\n");
> +	if (vdev->migration_flags & VFIO_MIGRATION_P2P)
> +		seq_puts(seq, "p2p\n");
> +	if (vdev->migration_flags & VFIO_MIGRATION_PRE_COPY)
> +		seq_puts(seq, "pre-copy\n");
> +	if (vdev->log_ops)
> +		seq_puts(seq, "dirty-tracking\n");
> +
> +	return 0;
> +}
> +
>  void vfio_device_debugfs_init(struct vfio_device *vdev)
>  {
>  	struct device *dev = &vdev->device;
> @@ -72,6 +89,8 @@ void vfio_device_debugfs_init(struct vfio_device *vdev)
>  							vdev->debug_root);
>  		debugfs_create_devm_seqfile(dev, "state", vfio_dev_migration,
>  					    vfio_device_state_read);
> +		debugfs_create_devm_seqfile(dev, "features", vfio_dev_migration,
> +					    vfio_device_features_read);
>  	}
>  }
>  
> diff --git a/Documentation/ABI/testing/debugfs-vfio b/Documentation/ABI/testing/debugfs-vfio
> index 90f7c262f591306bdb99295ab4e857ca0e0b537a..70ec2d454686290e13380340dfd6a5a67a642533 100644
> --- a/Documentation/ABI/testing/debugfs-vfio
> +++ b/Documentation/ABI/testing/debugfs-vfio
> @@ -23,3 +23,9 @@ Contact:	Longfang Liu <liulongfang@...wei.com>
>  Description:	Read the live migration status of the vfio device.
>  		The contents of the state file reflects the migration state
>  		relative to those defined in the vfio_device_mig_state enum
> +
> +What:		/sys/kernel/debug/vfio/<device>/migration/features
> +Date:		Oct 2025
> +KernelVersion:	6.18
> +Contact:	Cédric Le Goater <clg@...hat.com>
> +Description:	Read the migration features of the vfio device.