Re: [PATCH 5/9] vfio/pci: Provide a user-facing name for BAR mappings

[Alex Williamson <alex@shazbot.org>]

On Thu, 16 Apr 2026 06:17:48 -0700
Matt Evans <mattev@meta.com> wrote:

> Since converting BAR mmap()s to using DMABUFs, we lose the original
> device path in /proc/<pid>/maps, lsof, etc.  Generate a debug-oriented
> synthetic 'filename' based on the cdev, plus BDF, plus resource index.
> 
> This applies only to BAR mappings via the VFIO device fd, as
> explicitly-exported DMABUFs are named by userspace via the
> DMA_BUF_SET_NAME ioctl.
> 
> Signed-off-by: Matt Evans <mattev@meta.com>
> ---
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index a12432825e5e..04c7733fe712 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -4,6 +4,7 @@
>  #include <linux/dma-buf-mapping.h>
>  #include <linux/pci-p2pdma.h>
>  #include <linux/dma-resv.h>
> +#include <uapi/linux/dma-buf.h>
>  
>  #include "vfio_pci_priv.h"
>  
> @@ -467,6 +468,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
>  {
>  	struct vfio_pci_dma_buf *priv;
>  	const unsigned int nr_ranges = 1;
> +	char *bufname;
>  	int ret;
>  
>  	priv = kzalloc_obj(*priv);
> @@ -479,6 +481,20 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
>  		goto err_free_priv;
>  	}
>  
> +	bufname = kzalloc(DMA_BUF_NAME_LEN, GFP_KERNEL);
> +	if (!bufname) {
> +		ret = -ENOMEM;
> +		goto err_free_phys;
> +	}
> +
> +	/*
> +	 * Maximum size of the friendly debug name is
> +	 * vfio1234567890:ffff:ff:3f.7-9 = 30, which fits within
> +	 * DMA_BUF_NAME_LEN.
> +	 */
> +	snprintf(bufname, DMA_BUF_NAME_LEN, "%s:%s/%x",
> +		 dev_name(&vdev->vdev.device), pci_name(vdev->pdev), res_index);

Comment suggests 9 is the max res_index that can be printed, but mmap
only directly supports standard BARs 0-5.  Comment also uses a '-'
while the code uses a '/'.  Thanks,

Alex