linux-kernel - Re: [PATCH v16 2/3] vfio/pci: implement range_intesect

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Date: Mon, 15 Jan 2024 21:19:33 -0800
From: Rahul Rameshbabu <rrameshbabu@...dia.com>
To: ankita@...dia.com
Cc: jgg@...dia.com, alex.williamson@...hat.com, yishaih@...dia.com,
 shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
 eric.auger@...hat.com, brett.creeley@....com, horms@...nel.org,
 aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
 targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
 apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
 anuaggarwal@...dia.com, mochs@...dia.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v16 2/3] vfio/pci: implement range_intesect_range to
 determine range overlap

On Mon, 15 Jan, 2024 21:15:15 +0000 <ankita@...dia.com> wrote:
> From: Ankit Agrawal <ankita@...dia.com>
>
> Add a helper function to determine an overlap between two ranges.
> If an overlap, the function returns the overlapping offset and size.
>
> The VFIO PCI variant driver emulates the PCI config space BAR offset
> registers. These offset may be accessed for read/write with a variety
> of lengths including sub-word sizes from sub-word offsets. The driver
> makes use of this helper function to read/write the targeted part of
> the emulated register.
>
> This is replicated from Yishai's work in
> https://lore.kernel.org/all/20231207102820.74820-10-yishaih@nvidia.com
>
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> Tested-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  drivers/vfio/pci/vfio_pci_config.c | 28 ++++++++++++++++++++++++++++
>  include/linux/vfio_pci_core.h      |  6 ++++++
>  2 files changed, 34 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 7e2e62ab0869..b77c96fbc4b2 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1966,3 +1966,31 @@ ssize_t vfio_pci_config_rw(struct vfio_pci_core_device *vdev, char __user *buf,
>  
>  	return done;
>  }
> +
> +bool range_intersect_range(loff_t range1_start, size_t count1,
> +			   loff_t range2_start, size_t count2,
> +			   loff_t *start_offset,
> +			   size_t *intersect_count,
> +			   size_t *register_offset)
> +{
> +	if (range1_start <= range2_start &&
> +	    range1_start + count1 > range2_start) {
> +		*start_offset = range2_start - range1_start;
> +		*intersect_count = min_t(size_t, count2,
> +					 range1_start + count1 - range2_start);
> +		*register_offset = 0;
> +		return true;
> +	}
> +
> +	if (range1_start > range2_start &&
> +	    range1_start < range2_start + count2) {
> +		*start_offset = 0;
> +		*intersect_count = min_t(size_t, count1,
> +					 range2_start + count2 - range1_start);
> +		*register_offset = range1_start - range2_start;
> +		return true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(range_intersect_range);

If this function is being exported, shouldn't the function name follow
the pattern of having the vfio_pci_core_* prefix like the rest of the
symbols exported in this file. Something like
vfio_pci_core_range_intersect_range?

--
Thanks,

Rahul Rameshbabu