2007-10-21 21:24:21 -04:00
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/*P:050 Lguest guests use a very simple method to describe devices. It's a
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* series of device descriptors contained just above the top of normal
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* memory.
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*
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* We use the standard "virtio" device infrastructure, which provides us with a
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* console, a network and a block driver. Each one expects some configuration
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* information and a "virtqueue" mechanism to send and receive data. :*/
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#include <linux/init.h>
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#include <linux/bootmem.h>
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#include <linux/lguest_launcher.h>
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#include <linux/virtio.h>
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#include <linux/virtio_config.h>
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#include <linux/interrupt.h>
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#include <linux/virtio_ring.h>
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#include <linux/err.h>
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#include <asm/io.h>
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#include <asm/paravirt.h>
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#include <asm/lguest_hcall.h>
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/* The pointer to our (page) of device descriptions. */
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static void *lguest_devices;
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/* Unique numbering for lguest devices. */
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static unsigned int dev_index;
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/* For Guests, device memory can be used as normal memory, so we cast away the
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* __iomem to quieten sparse. */
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static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
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{
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return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
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}
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static inline void lguest_unmap(void *addr)
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{
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iounmap((__force void __iomem *)addr);
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}
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/*D:100 Each lguest device is just a virtio device plus a pointer to its entry
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* in the lguest_devices page. */
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struct lguest_device {
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struct virtio_device vdev;
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/* The entry in the lguest_devices page for this device. */
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struct lguest_device_desc *desc;
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};
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/* Since the virtio infrastructure hands us a pointer to the virtio_device all
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* the time, it helps to have a curt macro to get a pointer to the struct
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* lguest_device it's enclosed in. */
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#define to_lgdev(vdev) container_of(vdev, struct lguest_device, vdev)
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/*D:130
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* Device configurations
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*
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* The configuration information for a device consists of a series of fields.
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2007-10-25 01:02:50 -04:00
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* We don't really care what they are: the Launcher set them up, and the driver
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* will look at them during setup.
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2007-10-21 21:24:21 -04:00
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*
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* For us these fields come immediately after that device's descriptor in the
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* lguest_devices page.
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*
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* Each field starts with a "type" byte, a "length" byte, then that number of
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* bytes of configuration information. The device descriptor tells us the
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* total configuration length so we know when we've reached the last field. */
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/* type + length bytes */
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#define FHDR_LEN 2
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/* This finds the first field of a given type for a device's configuration. */
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static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len)
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{
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struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
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int i;
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for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) {
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if (desc->config[i] == type) {
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/* Mark it used, so Host can know we looked at it, and
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* also so we won't find the same one twice. */
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desc->config[i] |= 0x80;
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/* Remember, the second byte is the length. */
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*len = desc->config[i+1];
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/* We return a pointer to the field header. */
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return desc->config + i;
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}
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}
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/* Not found: return NULL for failure. */
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return NULL;
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}
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/* Once they've found a field, getting a copy of it is easy. */
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static void lg_get(struct virtio_device *vdev, void *token,
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void *buf, unsigned len)
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{
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/* Check they didn't ask for more than the length of the field! */
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BUG_ON(len > ((u8 *)token)[1]);
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memcpy(buf, token + FHDR_LEN, len);
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}
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/* Setting the contents is also trivial. */
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static void lg_set(struct virtio_device *vdev, void *token,
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const void *buf, unsigned len)
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{
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BUG_ON(len > ((u8 *)token)[1]);
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memcpy(token + FHDR_LEN, buf, len);
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}
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/* The operations to get and set the status word just access the status field
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* of the device descriptor. */
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static u8 lg_get_status(struct virtio_device *vdev)
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{
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return to_lgdev(vdev)->desc->status;
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}
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static void lg_set_status(struct virtio_device *vdev, u8 status)
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{
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to_lgdev(vdev)->desc->status = status;
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}
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/*
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* Virtqueues
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*
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* The other piece of infrastructure virtio needs is a "virtqueue": a way of
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* the Guest device registering buffers for the other side to read from or
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* write into (ie. send and receive buffers). Each device can have multiple
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2007-10-25 01:02:50 -04:00
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* virtqueues: for example the console driver uses one queue for sending and
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* another for receiving.
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2007-10-21 21:24:21 -04:00
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*
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* Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
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* already exists in virtio_ring.c. We just need to connect it up.
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*
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* We start with the information we need to keep about each virtqueue.
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*/
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/*D:140 This is the information we remember about each virtqueue. */
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struct lguest_vq_info
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{
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/* A copy of the information contained in the device config. */
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struct lguest_vqconfig config;
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/* The address where we mapped the virtio ring, so we can unmap it. */
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void *pages;
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};
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/* When the virtio_ring code wants to prod the Host, it calls us here and we
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* make a hypercall. We hand the page number of the virtqueue so the Host
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* knows which virtqueue we're talking about. */
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static void lg_notify(struct virtqueue *vq)
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{
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/* We store our virtqueue information in the "priv" pointer of the
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* virtqueue structure. */
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struct lguest_vq_info *lvq = vq->priv;
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hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
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}
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/* This routine finds the first virtqueue described in the configuration of
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* this device and sets it up.
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*
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* This is kind of an ugly duckling. It'd be nicer to have a standard
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* representation of a virtqueue in the configuration space, but it seems that
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2007-10-25 01:02:50 -04:00
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* everyone wants to do it differently. The KVM coders want the Guest to
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2007-10-21 21:24:21 -04:00
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* allocate its own pages and tell the Host where they are, but for lguest it's
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* simpler for the Host to simply tell us where the pages are.
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*
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* So we provide devices with a "find virtqueue and set it up" function. */
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static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
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bool (*callback)(struct virtqueue *vq))
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{
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struct lguest_vq_info *lvq;
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struct virtqueue *vq;
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unsigned int len;
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void *token;
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int err;
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/* Look for a field of the correct type to mark a virtqueue. Note that
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* if this succeeds, then the type will be changed so it won't be found
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* again, and future lg_find_vq() calls will find the next
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* virtqueue (if any). */
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token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len);
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if (!token)
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return ERR_PTR(-ENOENT);
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lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
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if (!lvq)
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return ERR_PTR(-ENOMEM);
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/* Note: we could use a configuration space inside here, just like we
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* do for the device. This would allow expansion in future, because
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* our configuration system is designed to be expansible. But this is
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* way easier. */
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if (len != sizeof(lvq->config)) {
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dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len);
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err = -EIO;
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goto free_lvq;
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}
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/* Make a copy of the "struct lguest_vqconfig" field. We need a copy
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* because the config space might not be aligned correctly. */
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vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config));
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/* Figure out how many pages the ring will take, and map that memory */
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lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
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2007-11-11 21:39:18 -05:00
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DIV_ROUND_UP(vring_size(lvq->config.num,
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PAGE_SIZE),
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2007-10-21 21:24:21 -04:00
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PAGE_SIZE));
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if (!lvq->pages) {
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err = -ENOMEM;
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goto free_lvq;
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}
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/* OK, tell virtio_ring.c to set up a virtqueue now we know its size
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* and we've got a pointer to its pages. */
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vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages,
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lg_notify, callback);
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if (!vq) {
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err = -ENOMEM;
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goto unmap;
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}
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/* Tell the interrupt for this virtqueue to go to the virtio_ring
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* interrupt handler. */
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/* FIXME: We used to have a flag for the Host to tell us we could use
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* the interrupt as a source of randomness: it'd be nice to have that
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* back.. */
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err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
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vdev->dev.bus_id, vq);
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if (err)
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goto destroy_vring;
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/* Last of all we hook up our 'struct lguest_vq_info" to the
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* virtqueue's priv pointer. */
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vq->priv = lvq;
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return vq;
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destroy_vring:
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vring_del_virtqueue(vq);
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unmap:
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lguest_unmap(lvq->pages);
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free_lvq:
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kfree(lvq);
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return ERR_PTR(err);
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}
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/*:*/
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/* Cleaning up a virtqueue is easy */
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static void lg_del_vq(struct virtqueue *vq)
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{
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struct lguest_vq_info *lvq = vq->priv;
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/* Tell virtio_ring.c to free the virtqueue. */
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vring_del_virtqueue(vq);
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/* Unmap the pages containing the ring. */
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lguest_unmap(lvq->pages);
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/* Free our own queue information. */
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kfree(lvq);
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}
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/* The ops structure which hooks everything together. */
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static struct virtio_config_ops lguest_config_ops = {
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.find = lg_find,
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.get = lg_get,
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.set = lg_set,
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.get_status = lg_get_status,
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.set_status = lg_set_status,
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.find_vq = lg_find_vq,
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.del_vq = lg_del_vq,
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};
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/* The root device for the lguest virtio devices. This makes them appear as
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* /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
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static struct device lguest_root = {
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.parent = NULL,
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.bus_id = "lguest",
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};
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/*D:120 This is the core of the lguest bus: actually adding a new device.
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* It's a separate function because it's neater that way, and because an
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* earlier version of the code supported hotplug and unplug. They were removed
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* early on because they were never used.
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*
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* As Andrew Tridgell says, "Untested code is buggy code".
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*
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* It's worth reading this carefully: we start with a pointer to the new device
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* descriptor in the "lguest_devices" page. */
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static void add_lguest_device(struct lguest_device_desc *d)
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{
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struct lguest_device *ldev;
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|
2007-10-25 01:02:50 -04:00
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/* Start with zeroed memory; Linux's device layer seems to count on
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* it. */
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2007-10-21 21:24:21 -04:00
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ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
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if (!ldev) {
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printk(KERN_EMERG "Cannot allocate lguest dev %u\n",
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dev_index++);
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return;
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}
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/* This devices' parent is the lguest/ dir. */
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ldev->vdev.dev.parent = &lguest_root;
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/* We have a unique device index thanks to the dev_index counter. */
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ldev->vdev.index = dev_index++;
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/* The device type comes straight from the descriptor. There's also a
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* device vendor field in the virtio_device struct, which we leave as
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* 0. */
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ldev->vdev.id.device = d->type;
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/* We have a simple set of routines for querying the device's
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* configuration information and setting its status. */
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ldev->vdev.config = &lguest_config_ops;
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/* And we remember the device's descriptor for lguest_config_ops. */
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ldev->desc = d;
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/* register_virtio_device() sets up the generic fields for the struct
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* virtio_device and calls device_register(). This makes the bus
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* infrastructure look for a matching driver. */
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if (register_virtio_device(&ldev->vdev) != 0) {
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printk(KERN_ERR "Failed to register lguest device %u\n",
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ldev->vdev.index);
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kfree(ldev);
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}
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}
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/*D:110 scan_devices() simply iterates through the device page. The type 0 is
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* reserved to mean "end of devices". */
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static void scan_devices(void)
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{
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unsigned int i;
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struct lguest_device_desc *d;
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/* We start at the page beginning, and skip over each entry. */
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for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) {
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d = lguest_devices + i;
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/* Once we hit a zero, stop. */
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if (d->type == 0)
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break;
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add_lguest_device(d);
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}
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}
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/*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
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* lguest device infrastructure. We check that we are a Guest by checking
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* pv_info.name: there are other ways of checking, but this seems most
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* obvious to me.
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*
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* So we can access the "struct lguest_device_desc"s easily, we map that memory
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* and store the pointer in the global "lguest_devices". Then we register a
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* root device from which all our devices will hang (this seems to be the
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* correct sysfs incantation).
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*
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* Finally we call scan_devices() which adds all the devices found in the
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* lguest_devices page. */
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static int __init lguest_devices_init(void)
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{
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if (strcmp(pv_info.name, "lguest") != 0)
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return 0;
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if (device_register(&lguest_root) != 0)
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panic("Could not register lguest root");
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/* Devices are in a single page above top of "normal" mem */
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lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
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scan_devices();
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return 0;
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}
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/* We do this after core stuff, but before the drivers. */
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postcore_initcall(lguest_devices_init);
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/*D:150 At this point in the journey we used to now wade through the lguest
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* devices themselves: net, block and console. Since they're all now virtio
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* devices rather than lguest-specific, I've decided to ignore them. Mostly,
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* they're kind of boring. But this does mean you'll never experience the
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* thrill of reading the forbidden love scene buried deep in the block driver.
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*
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* "make Launcher" beckons, where we answer questions like "Where do Guests
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* come from?", and "What do you do when someone asks for optimization?". */
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