linux-kernel - [RFC PATCH 33/33] Add Xen virtual block device driver.

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Date:	Tue, 18 Jul 2006 08:01:56 -0500
From:	boutcher@...umn.edu (Dave Boutcher)
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com,
	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>
Subject: [RFC PATCH 33/33] Add Xen virtual block device driver.

On Tue, 18 Jul 2006 00:00:33 -0700, Chris Wright <chrisw@...s-sol.org> said:
> 
> The block device frontend driver allows the kernel to access block
> devices exported exported by a virtual machine containing a physical
> block device driver.

First, I think this belongs in drivers/block (and the network driver
belongs in drivers/net).  If we're going to bring xen to the party,
lets not leave it hiding out in a corner.

> +static void connect(struct blkfront_info *);
> +static void blkfront_closing(struct xenbus_device *);
> +static int blkfront_remove(struct xenbus_device *);
> +static int talk_to_backend(struct xenbus_device *, struct blkfront_info *);
> +static int setup_blkring(struct xenbus_device *, struct blkfront_info *);
> +
> +static void kick_pending_request_queues(struct blkfront_info *);
> +
> +static irqreturn_t blkif_int(int irq, void *dev_id, struct pt_regs *ptregs);
> +static void blkif_restart_queue(void *arg);
> +static void blkif_recover(struct blkfront_info *);
> +static void blkif_completion(struct blk_shadow *);
> +static void blkif_free(struct blkfront_info *, int);

I'm pretty sure you can rearrange the code to get rid of the forward
references. 

> +/**
> + * We are reconnecting to the backend, due to a suspend/resume, or a backend
> + * driver restart.  We tear down our blkif structure and recreate it, but
> + * leave the device-layer structures intact so that this is transparent to the
> + * rest of the kernel.
> + */
> +static int blkfront_resume(struct xenbus_device *dev)
> +{
> +	struct blkfront_info *info = dev->dev.driver_data;
> +	int err;
> +
> +	DPRINTK("blkfront_resume: %s\n", dev->nodename);
> +
> +	blkif_free(info, 1);
> +
> +	err = talk_to_backend(dev, info);
> +	if (!err)
> +		blkif_recover(info);
> +
> +	return err;
> +}
Should blkfront_resume grab blkif_io_lock?

> +	switch (backend_state) {
> +	case XenbusStateUnknown:
> +	case XenbusStateInitialising:
> +	case XenbusStateInitWait:
> +	case XenbusStateInitialised:
> +	case XenbusStateClosed:

This actually should get fixed elsewhere, but SillyCaps???

> +static inline int GET_ID_FROM_FREELIST(
> +	struct blkfront_info *info)
> +{
> +	unsigned long free = info->shadow_free;
> +	BUG_ON(free > BLK_RING_SIZE);
> +	info->shadow_free = info->shadow[free].req.id;
> +	info->shadow[free].req.id = 0x0fffffee; /* debug */
> +	return free;
> +}
> +
> +static inline void ADD_ID_TO_FREELIST(
> +	struct blkfront_info *info, unsigned long id)
> +{
> +	info->shadow[id].req.id  = info->shadow_free;
> +	info->shadow[id].request = 0;
> +	info->shadow_free = id;
> +}

A real nit..but why are these routines SHOUTING?

> +int blkif_release(struct inode *inode, struct file *filep)
> +{
> +	struct blkfront_info *info = inode->i_bdev->bd_disk->private_data;
> +	info->users--;
> +	if (info->users == 0) {

Hrm...this strikes me as racey.  Don't you need at least a memory
barrier here to handle SMP?


> +static struct xlbd_major_info xvd_major_info = {
> +	.major = 201,
> +	.type = &xvd_type_info
> +};

I've forgotten what the current policy is around new major numbers. 


Dave B
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