linux-kernel - Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification interface

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Date:	Wed, 06 May 2009 07:35:12 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	viro@...IV.linux.org.uk, davidel@...ilserver.org
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification
 interface

Al, Davide,

Gregory Haskins wrote:
> +
> +int
> +kvm_irqfd(struct kvm *kvm, int gsi, int flags)
> +{
> +	struct _irqfd *irqfd;
> +	struct file *file = NULL;
> +	int fd = -1;
> +	int ret;
> +
> +	irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
> +	if (!irqfd)
> +		return -ENOMEM;
> +
> +	irqfd->kvm = kvm;
> +	irqfd->gsi = gsi;
> +	INIT_LIST_HEAD(&irqfd->list);
> +	INIT_WORK(&irqfd->work, irqfd_inject);
> +
> +	/*
> +	 * We re-use eventfd for irqfd, and therefore will embed the eventfd
> +	 * lifetime in the irqfd.
> +	 */
> +	file = eventfd_file_create(0, 0);
> +	if (IS_ERR(file)) {
> +		ret = PTR_ERR(file);
> +		goto fail;
> +	}
> +
> +	irqfd->file = file;
> +
> +	/*
> +	 * Install our own custom wake-up handling so we are notified via
> +	 * a callback whenever someone signals the underlying eventfd
> +	 */
> +	init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
> +	init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
> +
> +	ret = file->f_op->poll(file, &irqfd->pt);
> +	if (ret < 0)
> +		goto fail;
> +
> +	mutex_lock(&kvm->lock);
> +	list_add_tail(&irqfd->list, &kvm->irqfds);
> +	mutex_unlock(&kvm->lock);
> +
> +	ret = get_unused_fd();
> +	if (ret < 0)
> +		goto fail;
> +
> +	fd = ret;
> +
> +	fd_install(fd, file);
>   

Can you comment on whether this function needs to take an additional
reference on file here?  (one for the one held by userspace/fd, and the
other for irqfd->file)  My instinct is telling me this may be currently
broken, but I am not sure.

-Greg




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