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lguest.c

/*P:100 This is the Launcher code, a simple program which lays out the
 * "physical" memory for the new Guest by mapping the kernel image and the
 * virtual devices, then reads repeatedly from /dev/lguest to run the Guest.
:*/
#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <err.h>
#include <stdint.h>
#include <stdlib.h>
#include <elf.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <stdbool.h>
#include <errno.h>
#include <ctype.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <time.h>
#include <netinet/in.h>
#include <net/if.h>
#include <linux/sockios.h>
#include <linux/if_tun.h>
#include <sys/uio.h>
#include <termios.h>
#include <getopt.h>
#include <zlib.h>
#include <assert.h>
#include <sched.h>
#include "linux/lguest_launcher.h"
#include "linux/virtio_config.h"
#include "linux/virtio_net.h"
#include "linux/virtio_blk.h"
#include "linux/virtio_console.h"
#include "linux/virtio_ring.h"
#include "asm-x86/bootparam.h"
/*L:110 We can ignore the 38 include files we need for this program, but I do
 * want to draw attention to the use of kernel-style types.
 *
 * As Linus said, "C is a Spartan language, and so should your naming be."  I
 * like these abbreviations, so we define them here.  Note that u64 is always
 * unsigned long long, which works on all Linux systems: this means that we can
 * use %llu in printf for any u64. */
typedef unsigned long long u64;
typedef uint32_t u32;
typedef uint16_t u16;
typedef uint8_t u8;
/*:*/

#define PAGE_PRESENT 0x7      /* Present, RW, Execute */
#define NET_PEERNUM 1
#define BRIDGE_PFX "bridge:"
#ifndef SIOCBRADDIF
#define SIOCBRADDIF     0x89a2            /* add interface to bridge      */
#endif
/* We can have up to 256 pages for devices. */
#define DEVICE_PAGES 256
/* This will occupy 2 pages: it must be a power of 2. */
#define VIRTQUEUE_NUM 128

/*L:120 verbose is both a global flag and a macro.  The C preprocessor allows
 * this, and although I wouldn't recommend it, it works quite nicely here. */
static bool verbose;
#define verbose(args...) \
      do { if (verbose) printf(args); } while(0)
/*:*/

/* The pipe to send commands to the waker process */
static int waker_fd;
/* The pointer to the start of guest memory. */
static void *guest_base;
/* The maximum guest physical address allowed, and maximum possible. */
static unsigned long guest_limit, guest_max;

/* This is our list of devices. */
struct device_list
{
      /* Summary information about the devices in our list: ready to pass to
       * select() to ask which need servicing.*/
      fd_set infds;
      int max_infd;

      /* Counter to assign interrupt numbers. */
      unsigned int next_irq;

      /* Counter to print out convenient device numbers. */
      unsigned int device_num;

      /* The descriptor page for the devices. */
      u8 *descpage;

      /* The tail of the last descriptor. */
      unsigned int desc_used;

      /* A single linked list of devices. */
      struct device *dev;
      /* ... And an end pointer so we can easily append new devices */
      struct device **lastdev;
};

/* The list of Guest devices, based on command line arguments. */
static struct device_list devices;

/* The device structure describes a single device. */
00112 struct device
{
      /* The linked-list pointer. */
      struct device *next;

      /* The this device's descriptor, as mapped into the Guest. */
      struct lguest_device_desc *desc;

      /* The name of this device, for --verbose. */
      const char *name;

      /* If handle_input is set, it wants to be called when this file
       * descriptor is ready. */
      int fd;
      bool (*handle_input)(int fd, struct device *me);

      /* Any queues attached to this device */
      struct virtqueue *vq;

      /* Device-specific data. */
      void *priv;
};

/* The virtqueue structure describes a queue attached to a device. */
00136 struct virtqueue
{
      struct virtqueue *next;

      /* Which device owns me. */
      struct device *dev;

      /* The configuration for this queue. */
      struct lguest_vqconfig config;

      /* The actual ring of buffers. */
      struct vring vring;

      /* Last available index we saw. */
      u16 last_avail_idx;

      /* The routine to call when the Guest pings us. */
      void (*handle_output)(int fd, struct virtqueue *me);
};

/* Since guest is UP and we don't run at the same time, we don't need barriers.
 * But I include them in the code in case others copy it. */
#define wmb()

/* Convert an iovec element to the given type.
 *
 * This is a fairly ugly trick: we need to know the size of the type and
 * alignment requirement to check the pointer is kosher.  It's also nice to
 * have the name of the type in case we report failure.
 *
 * Typing those three things all the time is cumbersome and error prone, so we
 * have a macro which sets them all up and passes to the real function. */
#define convert(iov, type) \
      ((type *)_convert((iov), sizeof(type), __alignof__(type), #type))

static void *_convert(struct iovec *iov, size_t size, size_t align,
                  const char *name)
{
      if (iov->iov_len != size)
            errx(1, "Bad iovec size %zu for %s", iov->iov_len, name);
      if ((unsigned long)iov->iov_base % align != 0)
            errx(1, "Bad alignment %p for %s", iov->iov_base, name);
      return iov->iov_base;
}

/* The virtio configuration space is defined to be little-endian.  x86 is
 * little-endian too, but it's nice to be explicit so we have these helpers. */
#define cpu_to_le16(v16) (v16)
#define cpu_to_le32(v32) (v32)
#define cpu_to_le64(v64) (v64)
#define le16_to_cpu(v16) (v16)
#define le32_to_cpu(v32) (v32)
#define le64_to_cpu(v32) (v64)

/*L:100 The Launcher code itself takes us out into userspace, that scary place
 * where pointers run wild and free!  Unfortunately, like most userspace
 * programs, it's quite boring (which is why everyone likes to hack on the
 * kernel!).  Perhaps if you make up an Lguest Drinking Game at this point, it
 * will get you through this section.  Or, maybe not.
 *
 * The Launcher sets up a big chunk of memory to be the Guest's "physical"
 * memory and stores it in "guest_base".  In other words, Guest physical ==
 * Launcher virtual with an offset.
 *
 * This can be tough to get your head around, but usually it just means that we
 * use these trivial conversion functions when the Guest gives us it's
 * "physical" addresses: */
static void *from_guest_phys(unsigned long addr)
{
      return guest_base + addr;
}

static unsigned long to_guest_phys(const void *addr)
{
      return (addr - guest_base);
}

/*L:130
 * Loading the Kernel.
 *
 * We start with couple of simple helper routines.  open_or_die() avoids
 * error-checking code cluttering the callers: */
static int open_or_die(const char *name, int flags)
{
      int fd = open(name, flags);
      if (fd < 0)
            err(1, "Failed to open %s", name);
      return fd;
}

/* map_zeroed_pages() takes a number of pages. */
static void *map_zeroed_pages(unsigned int num)
{
      int fd = open_or_die("/dev/zero", O_RDONLY);
      void *addr;

      /* We use a private mapping (ie. if we write to the page, it will be
       * copied). */
      addr = mmap(NULL, getpagesize() * num,
                PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, fd, 0);
      if (addr == MAP_FAILED)
            err(1, "Mmaping %u pages of /dev/zero", num);

      return addr;
}

/* Get some more pages for a device. */
static void *get_pages(unsigned int num)
{
      void *addr = from_guest_phys(guest_limit);

      guest_limit += num * getpagesize();
      if (guest_limit > guest_max)
            errx(1, "Not enough memory for devices");
      return addr;
}

/* This routine is used to load the kernel or initrd.  It tries mmap, but if
 * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
 * it falls back to reading the memory in. */
static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
{
      ssize_t r;

      /* We map writable even though for some segments are marked read-only.
       * The kernel really wants to be writable: it patches its own
       * instructions.
       *
       * MAP_PRIVATE means that the page won't be copied until a write is
       * done to it.  This allows us to share untouched memory between
       * Guests. */
      if (mmap(addr, len, PROT_READ|PROT_WRITE|PROT_EXEC,
             MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
            return;

      /* pread does a seek and a read in one shot: saves a few lines. */
      r = pread(fd, addr, len, offset);
      if (r != len)
            err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
}

/* This routine takes an open vmlinux image, which is in ELF, and maps it into
 * the Guest memory.  ELF = Embedded Linking Format, which is the format used
 * by all modern binaries on Linux including the kernel.
 *
 * The ELF headers give *two* addresses: a physical address, and a virtual
 * address.  We use the physical address; the Guest will map itself to the
 * virtual address.
 *
 * We return the starting address. */
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
{
      Elf32_Phdr phdr[ehdr->e_phnum];
      unsigned int i;

      /* Sanity checks on the main ELF header: an x86 executable with a
       * reasonable number of correctly-sized program headers. */
      if (ehdr->e_type != ET_EXEC
          || ehdr->e_machine != EM_386
          || ehdr->e_phentsize != sizeof(Elf32_Phdr)
          || ehdr->e_phnum < 1 || ehdr->e_phnum > 65536U/sizeof(Elf32_Phdr))
            errx(1, "Malformed elf header");

      /* An ELF executable contains an ELF header and a number of "program"
       * headers which indicate which parts ("segments") of the program to
       * load where. */

      /* We read in all the program headers at once: */
      if (lseek(elf_fd, ehdr->e_phoff, SEEK_SET) < 0)
            err(1, "Seeking to program headers");
      if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
            err(1, "Reading program headers");

      /* Try all the headers: there are usually only three.  A read-only one,
       * a read-write one, and a "note" section which isn't loadable. */
      for (i = 0; i < ehdr->e_phnum; i++) {
            /* If this isn't a loadable segment, we ignore it */
            if (phdr[i].p_type != PT_LOAD)
                  continue;

            verbose("Section %i: size %i addr %p\n",
                  i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);

            /* We map this section of the file at its physical address. */
            map_at(elf_fd, from_guest_phys(phdr[i].p_paddr),
                   phdr[i].p_offset, phdr[i].p_filesz);
      }

      /* The entry point is given in the ELF header. */
      return ehdr->e_entry;
}

/*L:150 A bzImage, unlike an ELF file, is not meant to be loaded.  You're
 * supposed to jump into it and it will unpack itself.  We used to have to
 * perform some hairy magic because the unpacking code scared me.
 *
 * Fortunately, Jeremy Fitzhardinge convinced me it wasn't that hard and wrote
 * a small patch to jump over the tricky bits in the Guest, so now we just read
 * the funky header so we know where in the file to load, and away we go! */
static unsigned long load_bzimage(int fd)
{
      struct boot_params boot;
      int r;
      /* Modern bzImages get loaded at 1M. */
      void *p = from_guest_phys(0x100000);

      /* Go back to the start of the file and read the header.  It should be
       * a Linux boot header (see Documentation/i386/boot.txt) */
      lseek(fd, 0, SEEK_SET);
      read(fd, &boot, sizeof(boot));

      /* Inside the setup_hdr, we expect the magic "HdrS" */
      if (memcmp(&boot.hdr.header, "HdrS", 4) != 0)
            errx(1, "This doesn't look like a bzImage to me");

      /* Skip over the extra sectors of the header. */
      lseek(fd, (boot.hdr.setup_sects+1) * 512, SEEK_SET);

      /* Now read everything into memory. in nice big chunks. */
      while ((r = read(fd, p, 65536)) > 0)
            p += r;

      /* Finally, code32_start tells us where to enter the kernel. */
      return boot.hdr.code32_start;
}

/*L:140 Loading the kernel is easy when it's a "vmlinux", but most kernels
 * come wrapped up in the self-decompressing "bzImage" format.  With a little
 * work, we can load those, too. */
static unsigned long load_kernel(int fd)
{
      Elf32_Ehdr hdr;

      /* Read in the first few bytes. */
      if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
            err(1, "Reading kernel");

      /* If it's an ELF file, it starts with "\177ELF" */
      if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
            return map_elf(fd, &hdr);

      /* Otherwise we assume it's a bzImage, and try to unpack it */
      return load_bzimage(fd);
}

/* This is a trivial little helper to align pages.  Andi Kleen hated it because
 * it calls getpagesize() twice: "it's dumb code."
 *
 * Kernel guys get really het up about optimization, even when it's not
 * necessary.  I leave this code as a reaction against that. */
static inline unsigned long page_align(unsigned long addr)
{
      /* Add upwards and truncate downwards. */
      return ((addr + getpagesize()-1) & ~(getpagesize()-1));
}

/*L:180 An "initial ram disk" is a disk image loaded into memory along with
 * the kernel which the kernel can use to boot from without needing any
 * drivers.  Most distributions now use this as standard: the initrd contains
 * the code to load the appropriate driver modules for the current machine.
 *
 * Importantly, James Morris works for RedHat, and Fedora uses initrds for its
 * kernels.  He sent me this (and tells me when I break it). */
static unsigned long load_initrd(const char *name, unsigned long mem)
{
      int ifd;
      struct stat st;
      unsigned long len;

      ifd = open_or_die(name, O_RDONLY);
      /* fstat() is needed to get the file size. */
      if (fstat(ifd, &st) < 0)
            err(1, "fstat() on initrd '%s'", name);

      /* We map the initrd at the top of memory, but mmap wants it to be
       * page-aligned, so we round the size up for that. */
      len = page_align(st.st_size);
      map_at(ifd, from_guest_phys(mem - len), 0, st.st_size);
      /* Once a file is mapped, you can close the file descriptor.  It's a
       * little odd, but quite useful. */
      close(ifd);
      verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);

      /* We return the initrd size. */
      return len;
}

/* Once we know how much memory we have, we can construct simple linear page
 * tables which set virtual == physical which will get the Guest far enough
 * into the boot to create its own.
 *
 * We lay them out of the way, just below the initrd (which is why we need to
 * know its size). */
static unsigned long setup_pagetables(unsigned long mem,
                              unsigned long initrd_size)
{
      unsigned long *pgdir, *linear;
      unsigned int mapped_pages, i, linear_pages;
      unsigned int ptes_per_page = getpagesize()/sizeof(void *);

      mapped_pages = mem/getpagesize();

      /* Each PTE page can map ptes_per_page pages: how many do we need? */
      linear_pages = (mapped_pages + ptes_per_page-1)/ptes_per_page;

      /* We put the toplevel page directory page at the top of memory. */
      pgdir = from_guest_phys(mem) - initrd_size - getpagesize();

      /* Now we use the next linear_pages pages as pte pages */
      linear = (void *)pgdir - linear_pages*getpagesize();

      /* Linear mapping is easy: put every page's address into the mapping in
       * order.  PAGE_PRESENT contains the flags Present, Writable and
       * Executable. */
      for (i = 0; i < mapped_pages; i++)
            linear[i] = ((i * getpagesize()) | PAGE_PRESENT);

      /* The top level points to the linear page table pages above. */
      for (i = 0; i < mapped_pages; i += ptes_per_page) {
            pgdir[i/ptes_per_page]
                  = ((to_guest_phys(linear) + i*sizeof(void *))
                     | PAGE_PRESENT);
      }

      verbose("Linear mapping of %u pages in %u pte pages at %#lx\n",
            mapped_pages, linear_pages, to_guest_phys(linear));

      /* We return the top level (guest-physical) address: the kernel needs
       * to know where it is. */
      return to_guest_phys(pgdir);
}
/*:*/

/* Simple routine to roll all the commandline arguments together with spaces
 * between them. */
static void concat(char *dst, char *args[])
{
      unsigned int i, len = 0;

      for (i = 0; args[i]; i++) {
            strcpy(dst+len, args[i]);
            strcat(dst+len, " ");
            len += strlen(args[i]) + 1;
      }
      /* In case it's empty. */
      dst[len] = '\0';
}

/*L:185 This is where we actually tell the kernel to initialize the Guest.  We
 * saw the arguments it expects when we looked at initialize() in lguest_user.c:
 * the base of Guest "physical" memory, the top physical page to allow, the
 * top level pagetable and the entry point for the Guest. */
static int tell_kernel(unsigned long pgdir, unsigned long start)
{
      unsigned long args[] = { LHREQ_INITIALIZE,
                         (unsigned long)guest_base,
                         guest_limit / getpagesize(), pgdir, start };
      int fd;

      verbose("Guest: %p - %p (%#lx)\n",
            guest_base, guest_base + guest_limit, guest_limit);
      fd = open_or_die("/dev/lguest", O_RDWR);
      if (write(fd, args, sizeof(args)) < 0)
            err(1, "Writing to /dev/lguest");

      /* We return the /dev/lguest file descriptor to control this Guest */
      return fd;
}
/*:*/

static void add_device_fd(int fd)
{
      FD_SET(fd, &devices.infds);
      if (fd > devices.max_infd)
            devices.max_infd = fd;
}

/*L:200
 * The Waker.
 *
 * With console, block and network devices, we can have lots of input which we
 * need to process.  We could try to tell the kernel what file descriptors to
 * watch, but handing a file descriptor mask through to the kernel is fairly
 * icky.
 *
 * Instead, we fork off a process which watches the file descriptors and writes
 * the LHREQ_BREAK command to the /dev/lguest file descriptor to tell the Host
 * stop running the Guest.  This causes the Launcher to return from the
 * /dev/lguest read with -EAGAIN, where it will write to /dev/lguest to reset
 * the LHREQ_BREAK and wake us up again.
 *
 * This, of course, is merely a different *kind* of icky.
 */
static void wake_parent(int pipefd, int lguest_fd)
{
      /* Add the pipe from the Launcher to the fdset in the device_list, so
       * we watch it, too. */
      add_device_fd(pipefd);

      for (;;) {
            fd_set rfds = devices.infds;
            unsigned long args[] = { LHREQ_BREAK, 1 };

            /* Wait until input is ready from one of the devices. */
            select(devices.max_infd+1, &rfds, NULL, NULL, NULL);
            /* Is it a message from the Launcher? */
            if (FD_ISSET(pipefd, &rfds)) {
                  int fd;
                  /* If read() returns 0, it means the Launcher has
                   * exited.  We silently follow. */
                  if (read(pipefd, &fd, sizeof(fd)) == 0)
                        exit(0);
                  /* Otherwise it's telling us to change what file
                   * descriptors we're to listen to.  Positive means
                   * listen to a new one, negative means stop
                   * listening. */
                  if (fd >= 0)
                        FD_SET(fd, &devices.infds);
                  else
                        FD_CLR(-fd - 1, &devices.infds);
            } else /* Send LHREQ_BREAK command. */
                  write(lguest_fd, args, sizeof(args));
      }
}

/* This routine just sets up a pipe to the Waker process. */
static int setup_waker(int lguest_fd)
{
      int pipefd[2], child;

      /* We create a pipe to talk to the Waker, and also so it knows when the
       * Launcher dies (and closes pipe). */
      pipe(pipefd);
      child = fork();
      if (child == -1)
            err(1, "forking");

      if (child == 0) {
            /* We are the Waker: close the "writing" end of our copy of the
             * pipe and start waiting for input. */
            close(pipefd[1]);
            wake_parent(pipefd[0], lguest_fd);
      }
      /* Close the reading end of our copy of the pipe. */
      close(pipefd[0]);

      /* Here is the fd used to talk to the waker. */
      return pipefd[1];
}

/*
 * Device Handling.
 *
 * When the Guest gives us a buffer, it sends an array of addresses and sizes.
 * We need to make sure it's not trying to reach into the Launcher itself, so
 * we have a convenient routine which checks it and exits with an error message
 * if something funny is going on:
 */
static void *_check_pointer(unsigned long addr, unsigned int size,
                      unsigned int line)
{
      /* We have to separately check addr and addr+size, because size could
       * be huge and addr + size might wrap around. */
      if (addr >= guest_limit || addr + size >= guest_limit)
            errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
      /* We return a pointer for the caller's convenience, now we know it's
       * safe to use. */
      return from_guest_phys(addr);
}
/* A macro which transparently hands the line number to the real function. */
#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)

/* Each buffer in the virtqueues is actually a chain of descriptors.  This
 * function returns the next descriptor in the chain, or vq->vring.num if we're
 * at the end. */
static unsigned next_desc(struct virtqueue *vq, unsigned int i)
{
      unsigned int next;

      /* If this descriptor says it doesn't chain, we're done. */
      if (!(vq->vring.desc[i].flags & VRING_DESC_F_NEXT))
            return vq->vring.num;

      /* Check they're not leading us off end of descriptors. */
      next = vq->vring.desc[i].next;
      /* Make sure compiler knows to grab that: we don't want it changing! */
      wmb();

      if (next >= vq->vring.num)
            errx(1, "Desc next is %u", next);

      return next;
}

/* This looks in the virtqueue and for the first available buffer, and converts
 * it to an iovec for convenient access.  Since descriptors consist of some
 * number of output then some number of input descriptors, it's actually two
 * iovecs, but we pack them into one and note how many of each there were.
 *
 * This function returns the descriptor number found, or vq->vring.num (which
 * is never a valid descriptor number) if none was found. */
static unsigned get_vq_desc(struct virtqueue *vq,
                      struct iovec iov[],
                      unsigned int *out_num, unsigned int *in_num)
{
      unsigned int i, head;

      /* Check it isn't doing very strange things with descriptor numbers. */
      if ((u16)(vq->vring.avail->idx - vq->last_avail_idx) > vq->vring.num)
            errx(1, "Guest moved used index from %u to %u",
                 vq->last_avail_idx, vq->vring.avail->idx);

      /* If there's nothing new since last we looked, return invalid. */
      if (vq->vring.avail->idx == vq->last_avail_idx)
            return vq->vring.num;

      /* Grab the next descriptor number they're advertising, and increment
       * the index we've seen. */
      head = vq->vring.avail->ring[vq->last_avail_idx++ % vq->vring.num];

      /* If their number is silly, that's a fatal mistake. */
      if (head >= vq->vring.num)
            errx(1, "Guest says index %u is available", head);

      /* When we start there are none of either input nor output. */
      *out_num = *in_num = 0;

      i = head;
      do {
            /* Grab the first descriptor, and check it's OK. */
            iov[*out_num + *in_num].iov_len = vq->vring.desc[i].len;
            iov[*out_num + *in_num].iov_base
                  = check_pointer(vq->vring.desc[i].addr,
                              vq->vring.desc[i].len);
            /* If this is an input descriptor, increment that count. */
            if (vq->vring.desc[i].flags & VRING_DESC_F_WRITE)
                  (*in_num)++;
            else {
                  /* If it's an output descriptor, they're all supposed
                   * to come before any input descriptors. */
                  if (*in_num)
                        errx(1, "Descriptor has out after in");
                  (*out_num)++;
            }

            /* If we've got too many, that implies a descriptor loop. */
            if (*out_num + *in_num > vq->vring.num)
                  errx(1, "Looped descriptor");
      } while ((i = next_desc(vq, i)) != vq->vring.num);

      return head;
}

/* After we've used one of their buffers, we tell them about it.  We'll then
 * want to send them an interrupt, using trigger_irq(). */
static void add_used(struct virtqueue *vq, unsigned int head, int len)
{
      struct vring_used_elem *used;

      /* The virtqueue contains a ring of used buffers.  Get a pointer to the
       * next entry in that used ring. */
      used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
      used->id = head;
      used->len = len;
      /* Make sure buffer is written before we update index. */
      wmb();
      vq->vring.used->idx++;
}

/* This actually sends the interrupt for this virtqueue */
static void trigger_irq(int fd, struct virtqueue *vq)
{
      unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };

      /* If they don't want an interrupt, don't send one. */
      if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
            return;

      /* Send the Guest an interrupt tell them we used something up. */
      if (write(fd, buf, sizeof(buf)) != 0)
            err(1, "Triggering irq %i", vq->config.irq);
}

/* And here's the combo meal deal.  Supersize me! */
static void add_used_and_trigger(int fd, struct virtqueue *vq,
                         unsigned int head, int len)
{
      add_used(vq, head, len);
      trigger_irq(fd, vq);
}

/*
 * The Console
 *
 * Here is the input terminal setting we save, and the routine to restore them
 * on exit so the user gets their terminal back. */
static struct termios orig_term;
static void restore_term(void)
{
      tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
}

/* We associate some data with the console for our exit hack. */
struct console_abort
{
      /* How many times have they hit ^C? */
      int count;
      /* When did they start? */
      struct timeval start;
};

/* This is the routine which handles console input (ie. stdin). */
static bool handle_console_input(int fd, struct device *dev)
{
      int len;
      unsigned int head, in_num, out_num;
      struct iovec iov[dev->vq->vring.num];
      struct console_abort *abort = dev->priv;

      /* First we need a console buffer from the Guests's input virtqueue. */
      head = get_vq_desc(dev->vq, iov, &out_num, &in_num);

      /* If they're not ready for input, stop listening to this file
       * descriptor.  We'll start again once they add an input buffer. */
      if (head == dev->vq->vring.num)
            return false;

      if (out_num)
            errx(1, "Output buffers in console in queue?");

      /* This is why we convert to iovecs: the readv() call uses them, and so
       * it reads straight into the Guest's buffer. */
      len = readv(dev->fd, iov, in_num);
      if (len <= 0) {
            /* This implies that the console is closed, is /dev/null, or
             * something went terribly wrong. */
            warnx("Failed to get console input, ignoring console.");
            /* Put the input terminal back. */
            restore_term();
            /* Remove callback from input vq, so it doesn't restart us. */
            dev->vq->handle_output = NULL;
            /* Stop listening to this fd: don't call us again. */
            return false;
      }

      /* Tell the Guest about the new input. */
      add_used_and_trigger(fd, dev->vq, head, len);

      /* Three ^C within one second?  Exit.
       *
       * This is such a hack, but works surprisingly well.  Each ^C has to be
       * in a buffer by itself, so they can't be too fast.  But we check that
       * we get three within about a second, so they can't be too slow. */
      if (len == 1 && ((char *)iov[0].iov_base)[0] == 3) {
            if (!abort->count++)
                  gettimeofday(&abort->start, NULL);
            else if (abort->count == 3) {
                  struct timeval now;
                  gettimeofday(&now, NULL);
                  if (now.tv_sec <= abort->start.tv_sec+1) {
                        unsigned long args[] = { LHREQ_BREAK, 0 };
                        /* Close the fd so Waker will know it has to
                         * exit. */
                        close(waker_fd);
                        /* Just in case waker is blocked in BREAK, send
                         * unbreak now. */
                        write(fd, args, sizeof(args));
                        exit(2);
                  }
                  abort->count = 0;
            }
      } else
            /* Any other key resets the abort counter. */
            abort->count = 0;

      /* Everything went OK! */
      return true;
}

/* Handling output for console is simple: we just get all the output buffers
 * and write them to stdout. */
static void handle_console_output(int fd, struct virtqueue *vq)
{
      unsigned int head, out, in;
      int len;
      struct iovec iov[vq->vring.num];

      /* Keep getting output buffers from the Guest until we run out. */
      while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
            if (in)
                  errx(1, "Input buffers in output queue?");
            len = writev(STDOUT_FILENO, iov, out);
            add_used_and_trigger(fd, vq, head, len);
      }
}

/*
 * The Network
 *
 * Handling output for network is also simple: we get all the output buffers
 * and write them (ignoring the first element) to this device's file descriptor
 * (stdout). */
static void handle_net_output(int fd, struct virtqueue *vq)
{
      unsigned int head, out, in;
      int len;
      struct iovec iov[vq->vring.num];

      /* Keep getting output buffers from the Guest until we run out. */
      while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
            if (in)
                  errx(1, "Input buffers in output queue?");
            /* Check header, but otherwise ignore it (we told the Guest we
             * supported no features, so it shouldn't have anything
             * interesting). */
            (void)convert(&iov[0], struct virtio_net_hdr);
            len = writev(vq->dev->fd, iov+1, out-1);
            add_used_and_trigger(fd, vq, head, len);
      }
}

/* This is where we handle a packet coming in from the tun device to our
 * Guest. */
static bool handle_tun_input(int fd, struct device *dev)
{
      unsigned int head, in_num, out_num;
      int len;
      struct iovec iov[dev->vq->vring.num];
      struct virtio_net_hdr *hdr;

      /* First we need a network buffer from the Guests's recv virtqueue. */
      head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
      if (head == dev->vq->vring.num) {
            /* Now, it's expected that if we try to send a packet too
             * early, the Guest won't be ready yet.  Wait until the device
             * status says it's ready. */
            /* FIXME: Actually want DRIVER_ACTIVE here. */
            if (dev->desc->status & VIRTIO_CONFIG_S_DRIVER_OK)
                  warn("network: no dma buffer!");
            /* We'll turn this back on if input buffers are registered. */
            return false;
      } else if (out_num)
            errx(1, "Output buffers in network recv queue?");

      /* First element is the header: we set it to 0 (no features). */
      hdr = convert(&iov[0], struct virtio_net_hdr);
      hdr->flags = 0;
      hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;

      /* Read the packet from the device directly into the Guest's buffer. */
      len = readv(dev->fd, iov+1, in_num-1);
      if (len <= 0)
            err(1, "reading network");

      /* Tell the Guest about the new packet. */
      add_used_and_trigger(fd, dev->vq, head, sizeof(*hdr) + len);

      verbose("tun input packet len %i [%02x %02x] (%s)\n", len,
            ((u8 *)iov[1].iov_base)[0], ((u8 *)iov[1].iov_base)[1],
            head != dev->vq->vring.num ? "sent" : "discarded");

      /* All good. */
      return true;
}

/*L:215 This is the callback attached to the network and console input
 * virtqueues: it ensures we try again, in case we stopped console or net
 * delivery because Guest didn't have any buffers. */
static void enable_fd(int fd, struct virtqueue *vq)
{
      add_device_fd(vq->dev->fd);
      /* Tell waker to listen to it again */
      write(waker_fd, &vq->dev->fd, sizeof(vq->dev->fd));
}

/* This is the generic routine we call when the Guest uses LHCALL_NOTIFY. */
static void handle_output(int fd, unsigned long addr)
{
      struct device *i;
      struct virtqueue *vq;

      /* Check each virtqueue. */
      for (i = devices.dev; i; i = i->next) {
            for (vq = i->vq; vq; vq = vq->next) {
                  if (vq->config.pfn == addr/getpagesize()
                      && vq->handle_output) {
                        verbose("Output to %s\n", vq->dev->name);
                        vq->handle_output(fd, vq);
                        return;
                  }
            }
      }

      /* Early console write is done using notify on a nul-terminated string
       * in Guest memory. */
      if (addr >= guest_limit)
            errx(1, "Bad NOTIFY %#lx", addr);

      write(STDOUT_FILENO, from_guest_phys(addr),
            strnlen(from_guest_phys(addr), guest_limit - addr));
}

/* This is called when the Waker wakes us up: check for incoming file
 * descriptors. */
static void handle_input(int fd)
{
      /* select() wants a zeroed timeval to mean "don't wait". */
      struct timeval poll = { .tv_sec = 0, .tv_usec = 0 };

      for (;;) {
            struct device *i;
            fd_set fds = devices.infds;

            /* If nothing is ready, we're done. */
            if (select(devices.max_infd+1, &fds, NULL, NULL, &poll) == 0)
                  break;

            /* Otherwise, call the device(s) which have readable
             * file descriptors and a method of handling them.  */
            for (i = devices.dev; i; i = i->next) {
                  if (i->handle_input && FD_ISSET(i->fd, &fds)) {
                        int dev_fd;
                        if (i->handle_input(fd, i))
                              continue;

                        /* If handle_input() returns false, it means we
                         * should no longer service it.  Networking and
                         * console do this when there's no input
                         * buffers to deliver into.  Console also uses
                         * it when it discovers that stdin is
                         * closed. */
                        FD_CLR(i->fd, &devices.infds);
                        /* Tell waker to ignore it too, by sending a
                         * negative fd number (-1, since 0 is a valid
                         * FD number). */
                        dev_fd = -i->fd - 1;
                        write(waker_fd, &dev_fd, sizeof(dev_fd));
                  }
            }
      }
}

/*L:190
 * Device Setup
 *
 * All devices need a descriptor so the Guest knows it exists, and a "struct
 * device" so the Launcher can keep track of it.  We have common helper
 * routines to allocate them.
 *
 * This routine allocates a new "struct lguest_device_desc" from descriptor
 * table just above the Guest's normal memory.  It returns a pointer to that
 * descriptor. */
static struct lguest_device_desc *new_dev_desc(u16 type)
{
      struct lguest_device_desc *d;

      /* We only have one page for all the descriptors. */
      if (devices.desc_used + sizeof(*d) > getpagesize())
            errx(1, "Too many devices");

      /* We don't need to set config_len or status: page is 0 already. */
      d = (void *)devices.descpage + devices.desc_used;
      d->type = type;
      devices.desc_used += sizeof(*d);

      return d;
}

/* Each device descriptor is followed by some configuration information.
 * Each configuration field looks like: u8 type, u8 len, [... len bytes...].
 *
 * This routine adds a new field to an existing device's descriptor.  It only
 * works for the last device, but that's OK because that's how we use it. */
static void add_desc_field(struct device *dev, u8 type, u8 len, const void *c)
{
      /* This is the last descriptor, right? */
      assert(devices.descpage + devices.desc_used
             == (u8 *)(dev->desc + 1) + dev->desc->config_len);

      /* We only have one page of device descriptions. */
      if (devices.desc_used + 2 + len > getpagesize())
            errx(1, "Too many devices");

      /* Copy in the new config header: type then length. */
      devices.descpage[devices.desc_used++] = type;
      devices.descpage[devices.desc_used++] = len;
      memcpy(devices.descpage + devices.desc_used, c, len);
      devices.desc_used += len;

      /* Update the device descriptor length: two byte head then data. */
      dev->desc->config_len += 2 + len;
}

/* This routine adds a virtqueue to a device.  We specify how many descriptors
 * the virtqueue is to have. */
static void add_virtqueue(struct device *dev, unsigned int num_descs,
                    void (*handle_output)(int fd, struct virtqueue *me))
{
      unsigned int pages;
      struct virtqueue **i, *vq = malloc(sizeof(*vq));
      void *p;

      /* First we need some pages for this virtqueue. */
      pages = (vring_size(num_descs, getpagesize()) + getpagesize() - 1)
            / getpagesize();
      p = get_pages(pages);

      /* Initialize the virtqueue */
      vq->next = NULL;
      vq->last_avail_idx = 0;
      vq->dev = dev;

      /* Initialize the configuration. */
      vq->config.num = num_descs;
      vq->config.irq = devices.next_irq++;
      vq->config.pfn = to_guest_phys(p) / getpagesize();

      /* Initialize the vring. */
      vring_init(&vq->vring, num_descs, p, getpagesize());

      /* Add the configuration information to this device's descriptor. */
      add_desc_field(dev, VIRTIO_CONFIG_F_VIRTQUEUE,
                   sizeof(vq->config), &vq->config);

      /* Add to tail of list, so dev->vq is first vq, dev->vq->next is
       * second.  */
      for (i = &dev->vq; *i; i = &(*i)->next);
      *i = vq;

      /* Set the routine to call when the Guest does something to this
       * virtqueue. */
      vq->handle_output = handle_output;

      /* Set the "Don't Notify Me" flag if we don't have a handler */
      if (!handle_output)
            vq->vring.used->flags = VRING_USED_F_NO_NOTIFY;
}

/* This routine does all the creation and setup of a new device, including
 * calling new_dev_desc() to allocate the descriptor and device memory. */
static struct device *new_device(const char *name, u16 type, int fd,
                         bool (*handle_input)(int, struct device *))
{
      struct device *dev = malloc(sizeof(*dev));

      /* Append to device list.  Prepending to a single-linked list is
       * easier, but the user expects the devices to be arranged on the bus
       * in command-line order.  The first network device on the command line
       * is eth0, the first block device /dev/vda, etc. */
      *devices.lastdev = dev;
      dev->next = NULL;
      devices.lastdev = &dev->next;

      /* Now we populate the fields one at a time. */
      dev->fd = fd;
      /* If we have an input handler for this file descriptor, then we add it
       * to the device_list's fdset and maxfd. */
      if (handle_input)
            add_device_fd(dev->fd);
      dev->desc = new_dev_desc(type);
      dev->handle_input = handle_input;
      dev->name = name;
      dev->vq = NULL;
      return dev;
}

/* Our first setup routine is the console.  It's a fairly simple device, but
 * UNIX tty handling makes it uglier than it could be. */
static void setup_console(void)
{
      struct device *dev;

      /* If we can save the initial standard input settings... */
      if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
            struct termios term = orig_term;
            /* Then we turn off echo, line buffering and ^C etc.  We want a
             * raw input stream to the Guest. */
            term.c_lflag &= ~(ISIG|ICANON|ECHO);
            tcsetattr(STDIN_FILENO, TCSANOW, &term);
            /* If we exit gracefully, the original settings will be
             * restored so the user can see what they're typing. */
            atexit(restore_term);
      }

      dev = new_device("console", VIRTIO_ID_CONSOLE,
                   STDIN_FILENO, handle_console_input);
      /* We store the console state in dev->priv, and initialize it. */
      dev->priv = malloc(sizeof(struct console_abort));
      ((struct console_abort *)dev->priv)->count = 0;

      /* The console needs two virtqueues: the input then the output.  When
       * they put something the input queue, we make sure we're listening to
       * stdin.  When they put something in the output queue, we write it to
       * stdout. */
      add_virtqueue(dev, VIRTQUEUE_NUM, enable_fd);
      add_virtqueue(dev, VIRTQUEUE_NUM, handle_console_output);

      verbose("device %u: console\n", devices.device_num++);
}
/*:*/

/*M:010 Inter-guest networking is an interesting area.  Simplest is to have a
 * --sharenet=<name> option which opens or creates a named pipe.  This can be
 * used to send packets to another guest in a 1:1 manner.
 *
 * More sopisticated is to use one of the tools developed for project like UML
 * to do networking.
 *
 * Faster is to do virtio bonding in kernel.  Doing this 1:1 would be
 * completely generic ("here's my vring, attach to your vring") and would work
 * for any traffic.  Of course, namespace and permissions issues need to be
 * dealt with.  A more sophisticated "multi-channel" virtio_net.c could hide
 * multiple inter-guest channels behind one interface, although it would
 * require some manner of hotplugging new virtio channels.
 *
 * Finally, we could implement a virtio network switch in the kernel. :*/

static u32 str2ip(const char *ipaddr)
{
      unsigned int byte[4];

      sscanf(ipaddr, "%u.%u.%u.%u", &byte[0], &byte[1], &byte[2], &byte[3]);
      return (byte[0] << 24) | (byte[1] << 16) | (byte[2] << 8) | byte[3];
}

/* This code is "adapted" from libbridge: it attaches the Host end of the
 * network device to the bridge device specified by the command line.
 *
 * This is yet another James Morris contribution (I'm an IP-level guy, so I
 * dislike bridging), and I just try not to break it. */
static void add_to_bridge(int fd, const char *if_name, const char *br_name)
{
      int ifidx;
      struct ifreq ifr;

      if (!*br_name)
            errx(1, "must specify bridge name");

      ifidx = if_nametoindex(if_name);
      if (!ifidx)
            errx(1, "interface %s does not exist!", if_name);

      strncpy(ifr.ifr_name, br_name, IFNAMSIZ);
      ifr.ifr_ifindex = ifidx;
      if (ioctl(fd, SIOCBRADDIF, &ifr) < 0)
            err(1, "can't add %s to bridge %s", if_name, br_name);
}

/* This sets up the Host end of the network device with an IP address, brings
 * it up so packets will flow, the copies the MAC address into the hwaddr
 * pointer. */
static void configure_device(int fd, const char *devname, u32 ipaddr,
                       unsigned char hwaddr[6])
{
      struct ifreq ifr;
      struct sockaddr_in *sin = (struct sockaddr_in *)&ifr.ifr_addr;

      /* Don't read these incantations.  Just cut & paste them like I did! */
      memset(&ifr, 0, sizeof(ifr));
      strcpy(ifr.ifr_name, devname);
      sin->sin_family = AF_INET;
      sin->sin_addr.s_addr = htonl(ipaddr);
      if (ioctl(fd, SIOCSIFADDR, &ifr) != 0)
            err(1, "Setting %s interface address", devname);
      ifr.ifr_flags = IFF_UP;
      if (ioctl(fd, SIOCSIFFLAGS, &ifr) != 0)
            err(1, "Bringing interface %s up", devname);

      /* SIOC stands for Socket I/O Control.  G means Get (vs S for Set
       * above).  IF means Interface, and HWADDR is hardware address.
       * Simple! */
      if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
            err(1, "getting hw address for %s", devname);
      memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);
}

/*L:195 Our network is a Host<->Guest network.  This can either use bridging or
 * routing, but the principle is the same: it uses the "tun" device to inject
 * packets into the Host as if they came in from a normal network card.  We
 * just shunt packets between the Guest and the tun device. */
static void setup_tun_net(const char *arg)
{
      struct device *dev;
      struct ifreq ifr;
      int netfd, ipfd;
      u32 ip;
      const char *br_name = NULL;
      u8 hwaddr[6];

      /* We open the /dev/net/tun device and tell it we want a tap device.  A
       * tap device is like a tun device, only somehow different.  To tell
       * the truth, I completely blundered my way through this code, but it
       * works now! */
      netfd = open_or_die("/dev/net/tun", O_RDWR);
      memset(&ifr, 0, sizeof(ifr));
      ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
      strcpy(ifr.ifr_name, "tap%d");
      if (ioctl(netfd, TUNSETIFF, &ifr) != 0)
            err(1, "configuring /dev/net/tun");
      /* We don't need checksums calculated for packets coming in this
       * device: trust us! */
      ioctl(netfd, TUNSETNOCSUM, 1);

      /* First we create a new network device. */
      dev = new_device("net", VIRTIO_ID_NET, netfd, handle_tun_input);

      /* Network devices need a receive and a send queue, just like
       * console. */
      add_virtqueue(dev, VIRTQUEUE_NUM, enable_fd);
      add_virtqueue(dev, VIRTQUEUE_NUM, handle_net_output);

      /* We need a socket to perform the magic network ioctls to bring up the
       * tap interface, connect to the bridge etc.  Any socket will do! */
      ipfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
      if (ipfd < 0)
            err(1, "opening IP socket");

      /* If the command line was --tunnet=bridge:<name> do bridging. */
      if (!strncmp(BRIDGE_PFX, arg, strlen(BRIDGE_PFX))) {
            ip = INADDR_ANY;
            br_name = arg + strlen(BRIDGE_PFX);
            add_to_bridge(ipfd, ifr.ifr_name, br_name);
      } else /* It is an IP address to set up the device with */
            ip = str2ip(arg);

      /* Set up the tun device, and get the mac address for the interface. */
      configure_device(ipfd, ifr.ifr_name, ip, hwaddr);

      /* Tell Guest what MAC address to use. */
      add_desc_field(dev, VIRTIO_CONFIG_NET_MAC_F, sizeof(hwaddr), hwaddr);

      /* We don't seed the socket any more; setup is done. */
      close(ipfd);

      verbose("device %u: tun net %u.%u.%u.%u\n",
            devices.device_num++,
            (u8)(ip>>24),(u8)(ip>>16),(u8)(ip>>8),(u8)ip);
      if (br_name)
            verbose("attached to bridge: %s\n", br_name);
}

/* Our block (disk) device should be really simple: the Guest asks for a block
 * number and we read or write that position in the file.  Unfortunately, that
 * was amazingly slow: the Guest waits until the read is finished before
 * running anything else, even if it could have been doing useful work.
 *
 * We could use async I/O, except it's reputed to suck so hard that characters
 * actually go missing from your code when you try to use it.
 *
 * So we farm the I/O out to thread, and communicate with it via a pipe. */

/* This hangs off device->priv. */
struct vblk_info
{
      /* The size of the file. */
      off64_t len;

      /* The file descriptor for the file. */
      int fd;

      /* IO thread listens on this file descriptor [0]. */
      int workpipe[2];

      /* IO thread writes to this file descriptor to mark it done, then
       * Launcher triggers interrupt to Guest. */
      int done_fd;
};
/*:*/

/*L:210
 * The Disk
 *
 * Remember that the block device is handled by a separate I/O thread.  We head
 * straight into the core of that thread here:
 */
static bool service_io(struct device *dev)
{
      struct vblk_info *vblk = dev->priv;
      unsigned int head, out_num, in_num, wlen;
      int ret;
      struct virtio_blk_inhdr *in;
      struct virtio_blk_outhdr *out;
      struct iovec iov[dev->vq->vring.num];
      off64_t off;

      /* See if there's a request waiting.  If not, nothing to do. */
      head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
      if (head == dev->vq->vring.num)
            return false;

      /* Every block request should contain at least one output buffer
       * (detailing the location on disk and the type of request) and one
       * input buffer (to hold the result). */
      if (out_num == 0 || in_num == 0)
            errx(1, "Bad virtblk cmd %u out=%u in=%u",
                 head, out_num, in_num);

      out = convert(&iov[0], struct virtio_blk_outhdr);
      in = convert(&iov[out_num+in_num-1], struct virtio_blk_inhdr);
      off = out->sector * 512;

      /* The block device implements "barriers", where the Guest indicates
       * that it wants all previous writes to occur before this write.  We
       * don't have a way of asking our kernel to do a barrier, so we just
       * synchronize all the data in the file.  Pretty poor, no? */
      if (out->type & VIRTIO_BLK_T_BARRIER)
            fdatasync(vblk->fd);

      /* In general the virtio block driver is allowed to try SCSI commands.
       * It'd be nice if we supported eject, for example, but we don't. */
      if (out->type & VIRTIO_BLK_T_SCSI_CMD) {
            fprintf(stderr, "Scsi commands unsupported\n");
            in->status = VIRTIO_BLK_S_UNSUPP;
            wlen = sizeof(*in);
      } else if (out->type & VIRTIO_BLK_T_OUT) {
            /* Write */

            /* Move to the right location in the block file.  This can fail
             * if they try to write past end. */
            if (lseek64(vblk->fd, off, SEEK_SET) != off)
                  err(1, "Bad seek to sector %llu", out->sector);

            ret = writev(vblk->fd, iov+1, out_num-1);
            verbose("WRITE to sector %llu: %i\n", out->sector, ret);

            /* Grr... Now we know how long the descriptor they sent was, we
             * make sure they didn't try to write over the end of the block
             * file (possibly extending it). */
            if (ret > 0 && off + ret > vblk->len) {
                  /* Trim it back to the correct length */
                  ftruncate64(vblk->fd, vblk->len);
                  /* Die, bad Guest, die. */
                  errx(1, "Write past end %llu+%u", off, ret);
            }
            wlen = sizeof(*in);
            in->status = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
      } else {
            /* Read */

            /* Move to the right location in the block file.  This can fail
             * if they try to read past end. */
            if (lseek64(vblk->fd, off, SEEK_SET) != off)
                  err(1, "Bad seek to sector %llu", out->sector);

            ret = readv(vblk->fd, iov+1, in_num-1);
            verbose("READ from sector %llu: %i\n", out->sector, ret);
            if (ret >= 0) {
                  wlen = sizeof(*in) + ret;
                  in->status = VIRTIO_BLK_S_OK;
            } else {
                  wlen = sizeof(*in);
                  in->status = VIRTIO_BLK_S_IOERR;
            }
      }

      /* We can't trigger an IRQ, because we're not the Launcher.  It does
       * that when we tell it we're done. */
      add_used(dev->vq, head, wlen);
      return true;
}

/* This is the thread which actually services the I/O. */
static int io_thread(void *_dev)
{
      struct device *dev = _dev;
      struct vblk_info *vblk = dev->priv;
      char c;

      /* Close other side of workpipe so we get 0 read when main dies. */
      close(vblk->workpipe[1]);
      /* Close the other side of the done_fd pipe. */
      close(dev->fd);

      /* When this read fails, it means Launcher died, so we follow. */
      while (read(vblk->workpipe[0], &c, 1) == 1) {
            /* We acknowledge each request immediately to reduce latency,
             * rather than waiting until we've done them all.  I haven't
             * measured to see if it makes any difference. */
            while (service_io(dev))
                  write(vblk->done_fd, &c, 1);
      }
      return 0;
}

/* Now we've seen the I/O thread, we return to the Launcher to see what happens
 * when the thread tells us it's completed some I/O. */
static bool handle_io_finish(int fd, struct device *dev)
{
      char c;

      /* If the I/O thread died, presumably it printed the error, so we
       * simply exit. */
      if (read(dev->fd, &c, 1) != 1)
            exit(1);

      /* It did some work, so trigger the irq. */
      trigger_irq(fd, dev->vq);
      return true;
}

/* When the Guest submits some I/O, we just need to wake the I/O thread. */
static void handle_virtblk_output(int fd, struct virtqueue *vq)
{
      struct vblk_info *vblk = vq->dev->priv;
      char c = 0;

      /* Wake up I/O thread and tell it to go to work! */
      if (write(vblk->workpipe[1], &c, 1) != 1)
            /* Presumably it indicated why it died. */
            exit(1);
}

/*L:198 This actually sets up a virtual block device. */
static void setup_block_file(const char *filename)
{
      int p[2];
      struct device *dev;
      struct vblk_info *vblk;
      void *stack;
      u64 cap;
      unsigned int val;

      /* This is the pipe the I/O thread will use to tell us I/O is done. */
      pipe(p);

      /* The device responds to return from I/O thread. */
      dev = new_device("block", VIRTIO_ID_BLOCK, p[0], handle_io_finish);

      /* The device has one virtqueue, where the Guest places requests. */
      add_virtqueue(dev, VIRTQUEUE_NUM, handle_virtblk_output);

      /* Allocate the room for our own bookkeeping */
      vblk = dev->priv = malloc(sizeof(*vblk));

      /* First we open the file and store the length. */
      vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
      vblk->len = lseek64(vblk->fd, 0, SEEK_END);

      /* Tell Guest how many sectors this device has. */
      cap = cpu_to_le64(vblk->len / 512);
      add_desc_field(dev, VIRTIO_CONFIG_BLK_F_CAPACITY, sizeof(cap), &cap);

      /* Tell Guest not to put in too many descriptors at once: two are used
       * for the in and out elements. */
      val = cpu_to_le32(VIRTQUEUE_NUM - 2);
      add_desc_field(dev, VIRTIO_CONFIG_BLK_F_SEG_MAX, sizeof(val), &val);

      /* The I/O thread writes to this end of the pipe when done. */
      vblk->done_fd = p[1];

      /* This is the second pipe, which is how we tell the I/O thread about
       * more work. */
      pipe(vblk->workpipe);

      /* Create stack for thread and run it */
      stack = malloc(32768);
      if (clone(io_thread, stack + 32768, CLONE_VM, dev) == -1)
            err(1, "Creating clone");

      /* We don't need to keep the I/O thread's end of the pipes open. */
      close(vblk->done_fd);
      close(vblk->workpipe[0]);

      verbose("device %u: virtblock %llu sectors\n",
            devices.device_num, cap);
}
/* That's the end of device setup. */

/*L:220 Finally we reach the core of the Launcher, which runs the Guest, serves
 * its input and output, and finally, lays it to rest. */
static void __attribute__((noreturn)) run_guest(int lguest_fd)
{
      for (;;) {
            unsigned long args[] = { LHREQ_BREAK, 0 };
            unsigned long notify_addr;
            int readval;

            /* We read from the /dev/lguest device to run the Guest. */
            readval = read(lguest_fd, &notify_addr, sizeof(notify_addr));

            /* One unsigned long means the Guest did HCALL_NOTIFY */
            if (readval == sizeof(notify_addr)) {
                  verbose("Notify on address %#lx\n", notify_addr);
                  handle_output(lguest_fd, notify_addr);
                  continue;
            /* ENOENT means the Guest died.  Reading tells us why. */
            } else if (errno == ENOENT) {
                  char reason[1024] = { 0 };
                  read(lguest_fd, reason, sizeof(reason)-1);
                  errx(1, "%s", reason);
            /* EAGAIN means the Waker wanted us to look at some input.
             * Anything else means a bug or incompatible change. */
            } else if (errno != EAGAIN)
                  err(1, "Running guest failed");

            /* Service input, then unset the BREAK to release the Waker. */
            handle_input(lguest_fd);
            if (write(lguest_fd, args, sizeof(args)) < 0)
                  err(1, "Resetting break");
      }
}
/*
 * This is the end of the Launcher.  The good news: we are over halfway
 * through!  The bad news: the most fiendish part of the code still lies ahead
 * of us.
 *
 * Are you ready?  Take a deep breath and join me in the core of the Host, in
 * "make Host".
 :*/

static struct option opts[] = {
      { "verbose", 0, NULL, 'v' },
      { "tunnet", 1, NULL, 't' },
      { "block", 1, NULL, 'b' },
      { "initrd", 1, NULL, 'i' },
      { NULL },
};
static void usage(void)
{
      errx(1, "Usage: lguest [--verbose] "
           "[--tunnet=(<ipaddr>|bridge:<bridgename>)\n"
           "|--block=<filename>|--initrd=<filename>]...\n"
           "<mem-in-mb> vmlinux [args...]");
}

/*L:105 The main routine is where the real work begins: */
int main(int argc, char *argv[])
{
      /* Memory, top-level pagetable, code startpoint and size of the
       * (optional) initrd. */
      unsigned long mem = 0, pgdir, start, initrd_size = 0;
      /* Two temporaries and the /dev/lguest file descriptor. */
      int i, c, lguest_fd;
      /* The boot information for the Guest. */
      struct boot_params *boot;
      /* If they specify an initrd file to load. */
      const char *initrd_name = NULL;

      /* First we initialize the device list.  Since console and network
       * device receive input from a file descriptor, we keep an fdset
       * (infds) and the maximum fd number (max_infd) with the head of the
       * list.  We also keep a pointer to the last device, for easy appending
       * to the list.  Finally, we keep the next interrupt number to hand out
       * (1: remember that 0 is used by the timer). */
      FD_ZERO(&devices.infds);
      devices.max_infd = -1;
      devices.lastdev = &devices.dev;
      devices.next_irq = 1;

      /* We need to know how much memory so we can set up the device
       * descriptor and memory pages for the devices as we parse the command
       * line.  So we quickly look through the arguments to find the amount
       * of memory now. */
      for (i = 1; i < argc; i++) {
            if (argv[i][0] != '-') {
                  mem = atoi(argv[i]) * 1024 * 1024;
                  /* We start by mapping anonymous pages over all of
                   * guest-physical memory range.  This fills it with 0,
                   * and ensures that the Guest won't be killed when it
                   * tries to access it. */
                  guest_base = map_zeroed_pages(mem / getpagesize()
                                          + DEVICE_PAGES);
                  guest_limit = mem;
                  guest_max = mem + DEVICE_PAGES*getpagesize();
                  devices.descpage = get_pages(1);
                  break;
            }
      }

      /* The options are fairly straight-forward */
      while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
            switch (c) {
            case 'v':
                  verbose = true;
                  break;
            case 't':
                  setup_tun_net(optarg);
                  break;
            case 'b':
                  setup_block_file(optarg);
                  break;
            case 'i':
                  initrd_name = optarg;
                  break;
            default:
                  warnx("Unknown argument %s", argv[optind]);
                  usage();
            }
      }
      /* After the other arguments we expect memory and kernel image name,
       * followed by command line arguments for the kernel. */
      if (optind + 2 > argc)
            usage();

      verbose("Guest base is at %p\n", guest_base);

      /* We always have a console device */
      setup_console();

      /* Now we load the kernel */
      start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));

      /* Boot information is stashed at physical address 0 */
      boot = from_guest_phys(0);

      /* Map the initrd image if requested (at top of physical memory) */
      if (initrd_name) {
            initrd_size = load_initrd(initrd_name, mem);
            /* These are the location in the Linux boot header where the
             * start and size of the initrd are expected to be found. */
            boot->hdr.ramdisk_image = mem - initrd_size;
            boot->hdr.ramdisk_size = initrd_size;
            /* The bootloader type 0xFF means "unknown"; that's OK. */
            boot->hdr.type_of_loader = 0xFF;
      }

      /* Set up the initial linear pagetables, starting below the initrd. */
      pgdir = setup_pagetables(mem, initrd_size);

      /* The Linux boot header contains an "E820" memory map: ours is a
       * simple, single region. */
      boot->e820_entries = 1;
      boot->e820_map[0] = ((struct e820entry) { 0, mem, E820_RAM });
      /* The boot header contains a command line pointer: we put the command
       * line after the boot header. */
      boot->hdr.cmd_line_ptr = to_guest_phys(boot + 1);
      /* We use a simple helper to copy the arguments separated by spaces. */
      concat((char *)(boot + 1), argv+optind+2);

      /* Boot protocol version: 2.07 supports the fields for lguest. */
      boot->hdr.version = 0x207;

      /* The hardware_subarch value of "1" tells the Guest it's an lguest. */
      boot->hdr.hardware_subarch = 1;

      /* Tell the entry path not to try to reload segment registers. */
      boot->hdr.loadflags |= KEEP_SEGMENTS;

      /* We tell the kernel to initialize the Guest: this returns the open
       * /dev/lguest file descriptor. */
      lguest_fd = tell_kernel(pgdir, start);

      /* We fork off a child process, which wakes the Launcher whenever one
       * of the input file descriptors needs attention.  Otherwise we would
       * run the Guest until it tries to output something. */
      waker_fd = setup_waker(lguest_fd);

      /* Finally, run the Guest.  This doesn't return. */
      run_guest(lguest_fd);
}
/*:*/

/*M:999
 * Mastery is done: you now know everything I do.
 *
 * But surely you have seen code, features and bugs in your wanderings which
 * you now yearn to attack?  That is the real game, and I look forward to you
 * patching and forking lguest into the Your-Name-Here-visor.
 *
 * Farewell, and good coding!
 * Rusty Russell.
 */

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