linux-kernel - Re: [PATCH v2 4/7] xen/9pfs: connect to the backend

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Date:   Thu, 9 Mar 2017 10:40:38 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org,
        Stefano Stabellini <stefano@...reto.com>, jgross@...e.com,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: [PATCH v2 4/7] xen/9pfs: connect to the backend


> +
> +static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev,
> +		struct xen_9pfs_dataring *ring)
> +{
> +	int i;
> +	int ret = -ENOMEM;
> +
> +	init_waitqueue_head(&ring->wq);
> +	spin_lock_init(&ring->lock);
> +	INIT_WORK(&ring->work, p9_xen_response);
> +
> +	ring->intf = (struct xen_9pfs_data_intf *) get_zeroed_page(GFP_KERNEL | __GFP_ZERO);
> +	if (!ring->intf)
> +		return ret;
> +	ring->ref = gnttab_grant_foreign_access(dev->otherend_id, virt_to_gfn(ring->intf), 0);
> +	ring->bytes = (void*)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
> +			XEN_9PFS_RING_ORDER - (PAGE_SHIFT - XEN_PAGE_SHIFT));
> +	if (ring->bytes == NULL)
> +		goto out;
> +	for (i = 0; i < (1 << XEN_9PFS_RING_ORDER); i++)
> +		ring->intf->ref[i] = gnttab_grant_foreign_access(dev->otherend_id, virt_to_gfn(ring->bytes) + i, 0);

You need to handle gnttab_grant_foreign_access() returning an error. For
ring->ref too.

(and maybe wrap the line above)

> +	ring->ring.in = ring->bytes;

ring->ring? Maybe 'dataring' for the top-level structure?

BTW, do we really need 'bytes' member? It's always 'ring.in' AFAICT. You
could make it a union with 'ring' (the second 'ring' ;-)) if you want to
keep a pointer to the whole thing as a dedicated name.

-boris