/*P:050
   * Lguest guests use a very simple method to describe devices.  It's a
   * series of device descriptors contained just above the top of normal Guest
   * memory.
   *
   * We use the standard "virtio" device infrastructure, which provides us with a
   * console, a network and a block driver.  Each one expects some configuration
   * information and a "virtqueue" or two to send and receive data.
  :*/
  #include <linux/init.h>
  #include <linux/bootmem.h>
  #include <linux/lguest_launcher.h>
  #include <linux/virtio.h>
  #include <linux/virtio_config.h>
  #include <linux/interrupt.h>
  #include <linux/virtio_ring.h>
  #include <linux/err.h>
  #include <linux/export.h>
  #include <linux/slab.h>
  #include <asm/io.h>
  #include <asm/paravirt.h>
  #include <asm/lguest_hcall.h>
  
  /* The pointer to our (page) of device descriptions. */
  static void *lguest_devices;
  
  /*
   * For Guests, device memory can be used as normal memory, so we cast away the
   * __iomem to quieten sparse.
   */
  static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
  {
  	return (__force void *)ioremap_cache(phys_addr, PAGE_SIZE*pages);
  }
  
  static inline void lguest_unmap(void *addr)
  {
  	iounmap((__force void __iomem *)addr);
  }
  
  /*D:100
   * Each lguest device is just a virtio device plus a pointer to its entry
   * in the lguest_devices page.
   */
  struct lguest_device {
  	struct virtio_device vdev;
  
  	/* The entry in the lguest_devices page for this device. */
  	struct lguest_device_desc *desc;
  };
  
  /*
   * Since the virtio infrastructure hands us a pointer to the virtio_device all
   * the time, it helps to have a curt macro to get a pointer to the struct
   * lguest_device it's enclosed in.
   */
  #define to_lgdev(vd) container_of(vd, struct lguest_device, vdev)
  
  /*D:130
   * Device configurations
   *
   * The configuration information for a device consists of one or more
   * virtqueues, a feature bitmap, and some configuration bytes.  The
   * configuration bytes don't really matter to us: the Launcher sets them up, and
   * the driver will look at them during setup.
   *
   * A convenient routine to return the device's virtqueue config array:
   * immediately after the descriptor.
   */
  static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
  {
  	return (void *)(desc + 1);
  }
  
  /* The features come immediately after the virtqueues. */
  static u8 *lg_features(const struct lguest_device_desc *desc)
  {
  	return (void *)(lg_vq(desc) + desc->num_vq);
  }
  
  /* The config space comes after the two feature bitmasks. */
  static u8 *lg_config(const struct lguest_device_desc *desc)
  {
  	return lg_features(desc) + desc->feature_len * 2;
  }
  
  /* The total size of the config page used by this device (incl. desc) */
  static unsigned desc_size(const struct lguest_device_desc *desc)
  {
  	return sizeof(*desc)
  		+ desc->num_vq * sizeof(struct lguest_vqconfig)
  		+ desc->feature_len * 2
  		+ desc->config_len;
  }
  
  /* This gets the device's feature bits. */
  static u32 lg_get_features(struct virtio_device *vdev)
  {
  	unsigned int i;
  	u32 features = 0;
  	struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  	u8 *in_features = lg_features(desc);
  
  	/* We do this the slow but generic way. */
  	for (i = 0; i < min(desc->feature_len * 8, 32); i++)
  		if (in_features[i / 8] & (1 << (i % 8)))
  			features |= (1 << i);
  
  	return features;
  }
  
  /*
   * To notify on reset or feature finalization, we (ab)use the NOTIFY
   * hypercall, with the descriptor address of the device.
   */
  static void status_notify(struct virtio_device *vdev)
  {
  	unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
  
  	hcall(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset, 0, 0, 0);
  }
  
  /*
   * The virtio core takes the features the Host offers, and copies the ones
   * supported by the driver into the vdev->features array.  Once that's all
   * sorted out, this routine is called so we can tell the Host which features we
   * understand and accept.
   */
  static void lg_finalize_features(struct virtio_device *vdev)
  {
  	unsigned int i, bits;
  	struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  	/* Second half of bitmap is features we accept. */
  	u8 *out_features = lg_features(desc) + desc->feature_len;
  
  	/* Give virtio_ring a chance to accept features. */
  	vring_transport_features(vdev);
  
  	/*
  	 * The vdev->feature array is a Linux bitmask: this isn't the same as a
  	 * the simple array of bits used by lguest devices for features.  So we
  	 * do this slow, manual conversion which is completely general.
  	 */
  	memset(out_features, 0, desc->feature_len);
  	bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
  	for (i = 0; i < bits; i++) {
  		if (test_bit(i, vdev->features))
  			out_features[i / 8] |= (1 << (i % 8));
  	}
  
  	/* Tell Host we've finished with this device's feature negotiation */
  	status_notify(vdev);
  }
  
  /* Once they've found a field, getting a copy of it is easy. */
  static void lg_get(struct virtio_device *vdev, unsigned int offset,
  		   void *buf, unsigned len)
  {
  	struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  
  	/* Check they didn't ask for more than the length of the config! */
  	BUG_ON(offset + len > desc->config_len);
  	memcpy(buf, lg_config(desc) + offset, len);
  }
  
  /* Setting the contents is also trivial. */
  static void lg_set(struct virtio_device *vdev, unsigned int offset,
  		   const void *buf, unsigned len)
  {
  	struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  
  	/* Check they didn't ask for more than the length of the config! */
  	BUG_ON(offset + len > desc->config_len);
  	memcpy(lg_config(desc) + offset, buf, len);
  }
  
  /*
   * The operations to get and set the status word just access the status field
   * of the device descriptor.
   */
  static u8 lg_get_status(struct virtio_device *vdev)
  {
  	return to_lgdev(vdev)->desc->status;
  }
  
  static void lg_set_status(struct virtio_device *vdev, u8 status)
  {
  	BUG_ON(!status);
  	to_lgdev(vdev)->desc->status = status;
  
  	/* Tell Host immediately if we failed. */
  	if (status & VIRTIO_CONFIG_S_FAILED)
  		status_notify(vdev);
  }
  
  static void lg_reset(struct virtio_device *vdev)
  {
  	/* 0 status means "reset" */
  	to_lgdev(vdev)->desc->status = 0;
  	status_notify(vdev);
  }
  
  /*
   * Virtqueues
   *
   * The other piece of infrastructure virtio needs is a "virtqueue": a way of
   * the Guest device registering buffers for the other side to read from or
   * write into (ie. send and receive buffers).  Each device can have multiple
   * virtqueues: for example the console driver uses one queue for sending and
   * another for receiving.
   *
   * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
   * already exists in virtio_ring.c.  We just need to connect it up.
   *
   * We start with the information we need to keep about each virtqueue.
   */
  
  /*D:140 This is the information we remember about each virtqueue. */
  struct lguest_vq_info {
  	/* A copy of the information contained in the device config. */
  	struct lguest_vqconfig config;
  
  	/* The address where we mapped the virtio ring, so we can unmap it. */
  	void *pages;
  };
  
  /*
   * When the virtio_ring code wants to prod the Host, it calls us here and we
   * make a hypercall.  We hand the physical address of the virtqueue so the Host
   * knows which virtqueue we're talking about.
   */
  static bool lg_notify(struct virtqueue *vq)
  {
  	/*
  	 * We store our virtqueue information in the "priv" pointer of the
  	 * virtqueue structure.
  	 */
  	struct lguest_vq_info *lvq = vq->priv;
  
  	hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0, 0);
  	return true;
  }
  
  /* An extern declaration inside a C file is bad form.  Don't do it. */
  extern int lguest_setup_irq(unsigned int irq);
  
  /*
   * This routine finds the Nth virtqueue described in the configuration of
   * this device and sets it up.
   *
   * This is kind of an ugly duckling.  It'd be nicer to have a standard
   * representation of a virtqueue in the configuration space, but it seems that
   * everyone wants to do it differently.  The KVM coders want the Guest to
   * allocate its own pages and tell the Host where they are, but for lguest it's
   * simpler for the Host to simply tell us where the pages are.
   */
  static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
  				    unsigned index,
  				    void (*callback)(struct virtqueue *vq),
  				    const char *name)
  {
  	struct lguest_device *ldev = to_lgdev(vdev);
  	struct lguest_vq_info *lvq;
  	struct virtqueue *vq;
  	int err;
  
  	if (!name)
  		return NULL;
  
  	/* We must have this many virtqueues. */
  	if (index >= ldev->desc->num_vq)
  		return ERR_PTR(-ENOENT);
  
  	lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
  	if (!lvq)
  		return ERR_PTR(-ENOMEM);
  
  	/*
  	 * Make a copy of the "struct lguest_vqconfig" entry, which sits after
  	 * the descriptor.  We need a copy because the config space might not
  	 * be aligned correctly.
  	 */
  	memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
  
  	printk("Mapping virtqueue %i addr %lx
  ", index,
  	       (unsigned long)lvq->config.pfn << PAGE_SHIFT);
  	/* Figure out how many pages the ring will take, and map that memory */
  	lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
  				DIV_ROUND_UP(vring_size(lvq->config.num,
  							LGUEST_VRING_ALIGN),
  					     PAGE_SIZE));
  	if (!lvq->pages) {
  		err = -ENOMEM;
  		goto free_lvq;
  	}
  
  	/*
  	 * OK, tell virtio_ring.c to set up a virtqueue now we know its size
  	 * and we've got a pointer to its pages.  Note that we set weak_barriers
  	 * to 'true': the host just a(nother) SMP CPU, so we only need inter-cpu
  	 * barriers.
  	 */
  	vq = vring_new_virtqueue(index, lvq->config.num, LGUEST_VRING_ALIGN, vdev,
  				 true, lvq->pages, lg_notify, callback, name);
  	if (!vq) {
  		err = -ENOMEM;
  		goto unmap;
  	}
  
  	/* Make sure the interrupt is allocated. */
  	err = lguest_setup_irq(lvq->config.irq);
  	if (err)
  		goto destroy_vring;
  
  	/*
  	 * Tell the interrupt for this virtqueue to go to the virtio_ring
  	 * interrupt handler.
  	 *
  	 * FIXME: We used to have a flag for the Host to tell us we could use
  	 * the interrupt as a source of randomness: it'd be nice to have that
  	 * back.
  	 */
  	err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
  			  dev_name(&vdev->dev), vq);
  	if (err)
  		goto free_desc;
  
  	/*
  	 * Last of all we hook up our 'struct lguest_vq_info" to the
  	 * virtqueue's priv pointer.
  	 */
  	vq->priv = lvq;
  	return vq;
  
  free_desc:
  	irq_free_desc(lvq->config.irq);
  destroy_vring:
  	vring_del_virtqueue(vq);
  unmap:
  	lguest_unmap(lvq->pages);
  free_lvq:
  	kfree(lvq);
  	return ERR_PTR(err);
  }
  /*:*/
  
  /* Cleaning up a virtqueue is easy */
  static void lg_del_vq(struct virtqueue *vq)
  {
  	struct lguest_vq_info *lvq = vq->priv;
  
  	/* Release the interrupt */
  	free_irq(lvq->config.irq, vq);
  	/* Tell virtio_ring.c to free the virtqueue. */
  	vring_del_virtqueue(vq);
  	/* Unmap the pages containing the ring. */
  	lguest_unmap(lvq->pages);
  	/* Free our own queue information. */
  	kfree(lvq);
  }
  
  static void lg_del_vqs(struct virtio_device *vdev)
  {
  	struct virtqueue *vq, *n;
  
  	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
  		lg_del_vq(vq);
  }
  
  static int lg_find_vqs(struct virtio_device *vdev, unsigned nvqs,
  		       struct virtqueue *vqs[],
  		       vq_callback_t *callbacks[],
  		       const char *names[])
  {
  	struct lguest_device *ldev = to_lgdev(vdev);
  	int i;
  
  	/* We must have this many virtqueues. */
  	if (nvqs > ldev->desc->num_vq)
  		return -ENOENT;
  
  	for (i = 0; i < nvqs; ++i) {
  		vqs[i] = lg_find_vq(vdev, i, callbacks[i], names[i]);
  		if (IS_ERR(vqs[i]))
  			goto error;
  	}
  	return 0;
  
  error:
  	lg_del_vqs(vdev);
  	return PTR_ERR(vqs[i]);
  }
  
  static const char *lg_bus_name(struct virtio_device *vdev)
  {
  	return "";
  }
  
  /* The ops structure which hooks everything together. */
  static const struct virtio_config_ops lguest_config_ops = {
  	.get_features = lg_get_features,
  	.finalize_features = lg_finalize_features,
  	.get = lg_get,
  	.set = lg_set,
  	.get_status = lg_get_status,
  	.set_status = lg_set_status,
  	.reset = lg_reset,
  	.find_vqs = lg_find_vqs,
  	.del_vqs = lg_del_vqs,
  	.bus_name = lg_bus_name,
  };
  
  /*
   * The root device for the lguest virtio devices.  This makes them appear as
   * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2.
   */
  static struct device *lguest_root;
  
  /*D:120
   * This is the core of the lguest bus: actually adding a new device.
   * It's a separate function because it's neater that way, and because an
   * earlier version of the code supported hotplug and unplug.  They were removed
   * early on because they were never used.
   *
   * As Andrew Tridgell says, "Untested code is buggy code".
   *
   * It's worth reading this carefully: we start with a pointer to the new device
   * descriptor in the "lguest_devices" page, and the offset into the device
   * descriptor page so we can uniquely identify it if things go badly wrong.
   */
  static void add_lguest_device(struct lguest_device_desc *d,
  			      unsigned int offset)
  {
  	struct lguest_device *ldev;
  
  	/* Start with zeroed memory; Linux's device layer counts on it. */
  	ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
  	if (!ldev) {
  		printk(KERN_EMERG "Cannot allocate lguest dev %u type %u
  ",
  		       offset, d->type);
  		return;
  	}
  
  	/* This devices' parent is the lguest/ dir. */
  	ldev->vdev.dev.parent = lguest_root;
  	/*
  	 * The device type comes straight from the descriptor.  There's also a
  	 * device vendor field in the virtio_device struct, which we leave as
  	 * 0.
  	 */
  	ldev->vdev.id.device = d->type;
  	/*
  	 * We have a simple set of routines for querying the device's
  	 * configuration information and setting its status.
  	 */
  	ldev->vdev.config = &lguest_config_ops;
  	/* And we remember the device's descriptor for lguest_config_ops. */
  	ldev->desc = d;
  
  	/*
  	 * register_virtio_device() sets up the generic fields for the struct
  	 * virtio_device and calls device_register().  This makes the bus
  	 * infrastructure look for a matching driver.
  	 */
  	if (register_virtio_device(&ldev->vdev) != 0) {
  		printk(KERN_ERR "Failed to register lguest dev %u type %u
  ",
  		       offset, d->type);
  		kfree(ldev);
  	}
  }
  
  /*D:110
   * scan_devices() simply iterates through the device page.  The type 0 is
   * reserved to mean "end of devices".
   */
  static void scan_devices(void)
  {
  	unsigned int i;
  	struct lguest_device_desc *d;
  
  	/* We start at the page beginning, and skip over each entry. */
  	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
  		d = lguest_devices + i;
  
  		/* Once we hit a zero, stop. */
  		if (d->type == 0)
  			break;
  
  		printk("Device at %i has size %u
  ", i, desc_size(d));
  		add_lguest_device(d, i);
  	}
  }
  
  /*D:105
   * Fairly early in boot, lguest_devices_init() is called to set up the
   * lguest device infrastructure.  We check that we are a Guest by checking
   * pv_info.name: there are other ways of checking, but this seems most
   * obvious to me.
   *
   * So we can access the "struct lguest_device_desc"s easily, we map that memory
   * and store the pointer in the global "lguest_devices".  Then we register a
   * root device from which all our devices will hang (this seems to be the
   * correct sysfs incantation).
   *
   * Finally we call scan_devices() which adds all the devices found in the
   * lguest_devices page.
   */
  static int __init lguest_devices_init(void)
  {
  	if (strcmp(pv_info.name, "lguest") != 0)
  		return 0;
  
  	lguest_root = root_device_register("lguest");
  	if (IS_ERR(lguest_root))
  		panic("Could not register lguest root");
  
  	/* Devices are in a single page above top of "normal" mem */
  	lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
  
  	scan_devices();
  	return 0;
  }
  /* We do this after core stuff, but before the drivers. */
  postcore_initcall(lguest_devices_init);
  
  /*D:150
   * At this point in the journey we used to now wade through the lguest
   * devices themselves: net, block and console.  Since they're all now virtio
   * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
   * they're kind of boring.  But this does mean you'll never experience the
   * thrill of reading the forbidden love scene buried deep in the block driver.
   *
   * "make Launcher" beckons, where we answer questions like "Where do Guests
   * come from?", and "What do you do when someone asks for optimization?".
   */