linux-kernel - Re: [RFC PATCH v3 1/4] vfio: Define device specific irq type capability

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Date:   Wed, 26 Jun 2019 22:07:39 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     intel-gvt-dev@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kraxel@...hat.com,
        zhenyuw@...ux.intel.com, zhiyuan.lv@...el.com,
        zhi.a.wang@...el.com, kevin.tian@...el.com, hang.yuan@...el.com
Subject: Re: [RFC PATCH v3 1/4] vfio: Define device specific irq type
 capability

On Thu, 27 Jun 2019 11:37:59 +0800
Tina Zhang <tina.zhang@...el.com> wrote:

> Cap the number of irqs with fixed indexes and use capability chains
> to chain device specific irqs.
> 
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> ---
>  include/uapi/linux/vfio.h | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 02bb7ad6e986..600784acc4ac 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -444,11 +444,27 @@ struct vfio_irq_info {
>  #define VFIO_IRQ_INFO_MASKABLE		(1 << 1)
>  #define VFIO_IRQ_INFO_AUTOMASKED	(1 << 2)
>  #define VFIO_IRQ_INFO_NORESIZE		(1 << 3)
> +#define VFIO_IRQ_INFO_FLAG_CAPS		(1 << 4) /* Info supports caps */
>  	__u32	index;		/* IRQ index */
> +	__u32	cap_offset;	/* Offset within info struct of first cap */
>  	__u32	count;		/* Number of IRQs within this index */
>  };


This cannot be inserted into the middle of the structure, it breaks
compatibility with all existing userspace binaries.  I must be added to
the end of the structure.

>  #define VFIO_DEVICE_GET_IRQ_INFO	_IO(VFIO_TYPE, VFIO_BASE + 9)
>  
> +/*
> + * The irq type capability allows irqs unique to a specific device or
> + * class of devices to be exposed.
> + *
> + * The structures below define version 1 of this capability.
> + */
> +#define VFIO_IRQ_INFO_CAP_TYPE      3
> +
> +struct vfio_irq_info_cap_type {
> +	struct vfio_info_cap_header header;
> +	__u32 type;     /* global per bus driver */
> +	__u32 subtype;  /* type specific */
> +};
> +
>  /**
>   * VFIO_DEVICE_SET_IRQS - _IOW(VFIO_TYPE, VFIO_BASE + 10, struct vfio_irq_set)
>   *
> @@ -550,7 +566,8 @@ enum {
>  	VFIO_PCI_MSIX_IRQ_INDEX,
>  	VFIO_PCI_ERR_IRQ_INDEX,
>  	VFIO_PCI_REQ_IRQ_INDEX,
> -	VFIO_PCI_NUM_IRQS
> +	VFIO_PCI_NUM_IRQS = 5	/* Fixed user ABI, IRQ indexes >=5 use   */
> +				/* device specific cap to define content */
>  };
>  
>  /*