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Date:   Wed, 20 Apr 2022 14:44:31 -0400
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Subject: Re: [PATCH 09/18] xen/xenbus: add xenbus_setup_ring() service
 function
Content-Language: en-US
To:     Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
Cc:     Stefano Stabellini <sstabellini@kernel.org>
References: <20220420150942.31235-1-jgross@suse.com>
 <20220420150942.31235-10-jgross@suse.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
In-Reply-To: <20220420150942.31235-10-jgross@suse.com>
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On 4/20/22 11:09 AM, Juergen Gross wrote:
>   
> +/*
> + * xenbus_setup_ring
> + * @dev: xenbus device
> + * @vaddr: pointer to starting virtual address of the ring
> + * @nr_pages: number of pages to be granted
> + * @grefs: grant reference array to be filled in
> + *
> + * Allocate physically contiguous pages for a shared ring buffer and grant it
> + * to the peer of the given device. The ring buffer is initially filled with
> + * zeroes. The virtual address of the ring is stored at @vaddr and the
> + * grant references are stored in the @grefs array. In case of error @vaddr
> + * will be set to NULL and @grefs will be filled with INVALID_GRANT_REF.
> + */
> +int xenbus_setup_ring(struct xenbus_device *dev, gfp_t gfp, void **vaddr,
> +		      unsigned int nr_pages, grant_ref_t *grefs)
> +{
> +	unsigned long ring_size = nr_pages * XEN_PAGE_SIZE;
> +	unsigned int i;
> +	int ret;
> +
> +	*vaddr = alloc_pages_exact(ring_size, gfp | __GFP_ZERO);
> +	if (!*vaddr) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	ret = xenbus_grant_ring(dev, *vaddr, nr_pages, grefs);
> +	if (ret)
> +		goto err;
> +
> +	return 0;
> +
> + err:
> +	if (*vaddr)
> +		free_pages_exact(*vaddr, ring_size);
> +	for (i = 0; i < nr_pages; i++)
> +		grefs[i] = INVALID_GRANT_REF;
> +	*vaddr = NULL;
> +
> +	return ret;
> +}


We can create a wrapper around this function that will also call SHARED_RING_INIT() and FRONT_RING_INIT(). A bunch of drivers do that.


-boris