lguest: the documentation, example launcher

A brief document describing how to use lguest.  Because lguest doesn't have an
ABI we also include an example launcher in the Documentation directory.

[jmorris@namei.org: Fix up nat example in documentation]
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: James Morris <jmorris@namei.org>
Cc: Matias Zabaljauregui <matias.zabaljauregui@cern.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1012 insertions, 0 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
new file mode 100644
index 000000000000..1432b502a2d9
--- /dev/null
+++ b/Documentation/lguest/lguest.c
@@ -0,0 +1,1012 @@
+/* Simple program to layout "physical" memory for new lguest guest.
+ * Linked high to avoid likely physical memory.  */
+#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/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>
+typedef unsigned long long u64;
+typedef uint32_t u32;
+typedef uint16_t u16;
+typedef uint8_t u8;
+#include "../../include/linux/lguest_launcher.h"
+#include "../../include/asm-i386/e820.h"
+
+#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
+
+static bool verbose;
+#define verbose(args...) \
+        do { if (verbose) printf(args); } while(0)
+static int waker_fd;
+
+struct device_list
+{
+        fd_set infds;
+        int max_infd;
+
+        struct device *dev;
+        struct device **lastdev;
+};
+
+struct device
+{
+        struct device *next;
+        struct lguest_device_desc *desc;
+        void *mem;
+
+        /* Watch this fd if handle_input non-NULL. */
+        int fd;
+        bool (*handle_input)(int fd, struct device *me);
+
+        /* Watch DMA to this key if handle_input non-NULL. */
+        unsigned long watch_key;
+        u32 (*handle_output)(int fd, const struct iovec *iov,
+                             unsigned int num, struct device *me);
+
+        /* Device-specific data. */
+        void *priv;
+};
+
+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;
+}
+
+static void *map_zeroed_pages(unsigned long addr, unsigned int num)
+{
+        static int fd = -1;
+
+        if (fd == -1)
+                fd = open_or_die("/dev/zero", O_RDONLY);
+
+        if (mmap((void *)addr, getpagesize() * num,
+                 PROT_READ|PROT_WRITE|PROT_EXEC, MAP_FIXED|MAP_PRIVATE, fd, 0)
+            != (void *)addr)
+                err(1, "Mmaping %u pages of /dev/zero @%p", num, (void *)addr);
+        return (void *)addr;
+}
+
+/* Find magic string marking entry point, return entry point. */
+static unsigned long entry_point(void *start, void *end,
+                                 unsigned long page_offset)
+{
+        void *p;
+
+        for (p = start; p < end; p++)
+                if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
+                        return (long)p + strlen("GenuineLguest") + page_offset;
+
+        err(1, "Is this image a genuine lguest?");
+}
+
+/* Returns the entry point */
+static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
+                             unsigned long *page_offset)
+{
+        void *addr;
+        Elf32_Phdr phdr[ehdr->e_phnum];
+        unsigned int i;
+        unsigned long start = -1UL, end = 0;
+
+        /* Sanity checks. */
+        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");
+
+        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");
+
+        *page_offset = 0;
+        /* We map the loadable segments at virtual addresses corresponding
+         * to their physical addresses (our virtual == guest physical). */
+        for (i = 0; i < ehdr->e_phnum; i++) {
+                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 expect linear address space. */
+                if (!*page_offset)
+                        *page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
+                else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
+                        errx(1, "Page offset of section %i different", i);
+
+                if (phdr[i].p_paddr < start)
+                        start = phdr[i].p_paddr;
+                if (phdr[i].p_paddr + phdr[i].p_filesz > end)
+                        end = phdr[i].p_paddr + phdr[i].p_filesz;
+
+                /* We map everything private, writable. */
+                addr = mmap((void *)phdr[i].p_paddr,
+                            phdr[i].p_filesz,
+                            PROT_READ|PROT_WRITE|PROT_EXEC,
+                            MAP_FIXED|MAP_PRIVATE,
+                            elf_fd, phdr[i].p_offset);
+                if (addr != (void *)phdr[i].p_paddr)
+                        err(1, "Mmaping vmlinux seg %i gave %p not %p",
+                            i, addr, (void *)phdr[i].p_paddr);
+        }
+
+        return entry_point((void *)start, (void *)end, *page_offset);
+}
+
+/* This is amazingly reliable. */
+static unsigned long intuit_page_offset(unsigned char *img, unsigned long len)
+{
+        unsigned int i, possibilities[256] = { 0 };
+
+        for (i = 0; i + 4 < len; i++) {
+                /* mov 0xXXXXXXXX,%eax */
+                if (img[i] == 0xA1 && ++possibilities[img[i+4]] > 3)
+                        return (unsigned long)img[i+4] << 24;
+        }
+        errx(1, "could not determine page offset");
+}
+
+static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
+{
+        gzFile f;
+        int ret, len = 0;
+        void *img = (void *)0x100000;
+
+        f = gzdopen(fd, "rb");
+        while ((ret = gzread(f, img + len, 65536)) > 0)
+                len += ret;
+        if (ret < 0)
+                err(1, "reading image from bzImage");
+
+        verbose("Unpacked size %i addr %p\n", len, img);
+        *page_offset = intuit_page_offset(img, len);
+
+        return entry_point(img, img + len, *page_offset);
+}
+
+static unsigned long load_bzimage(int fd, unsigned long *page_offset)
+{
+        unsigned char c;
+        int state = 0;
+
+        /* Ugly brute force search for gzip header. */
+        while (read(fd, &c, 1) == 1) {
+                switch (state) {
+                case 0:
+                        if (c == 0x1F)
+                                state++;
+                        break;
+                case 1:
+                        if (c == 0x8B)
+                                state++;
+                        else
+                                state = 0;
+                        break;
+                case 2 ... 8:
+                        state++;
+                        break;
+                case 9:
+                        lseek(fd, -10, SEEK_CUR);
+                        if (c != 0x03) /* Compressed under UNIX. */
+                                state = -1;
+                        else
+                                return unpack_bzimage(fd, page_offset);
+                }
+        }
+        errx(1, "Could not find kernel in bzImage");
+}
+
+static unsigned long load_kernel(int fd, unsigned long *page_offset)
+{
+        Elf32_Ehdr hdr;
+
+        if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
+                err(1, "Reading kernel");
+
+        if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
+                return map_elf(fd, &hdr, page_offset);
+
+        return load_bzimage(fd, page_offset);
+}
+
+static inline unsigned long page_align(unsigned long addr)
+{
+        return ((addr + getpagesize()-1) & ~(getpagesize()-1));
+}
+
+/* initrd gets loaded at top of memory: return length. */
+static unsigned long load_initrd(const char *name, unsigned long mem)
+{
+        int ifd;
+        struct stat st;
+        unsigned long len;
+        void *iaddr;
+
+        ifd = open_or_die(name, O_RDONLY);
+        if (fstat(ifd, &st) < 0)
+                err(1, "fstat() on initrd '%s'", name);
+
+        len = page_align(st.st_size);
+        iaddr = mmap((void *)mem - len, st.st_size,
+                     PROT_READ|PROT_EXEC|PROT_WRITE,
+                     MAP_FIXED|MAP_PRIVATE, ifd, 0);
+        if (iaddr != (void *)mem - len)
+                err(1, "Mmaping initrd '%s' returned %p not %p",
+                    name, iaddr, (void *)mem - len);
+        close(ifd);
+        verbose("mapped initrd %s size=%lu @ %p\n", name, st.st_size, iaddr);
+        return len;
+}
+
+static unsigned long setup_pagetables(unsigned long mem,
+                                      unsigned long initrd_size,
+                                      unsigned long page_offset)
+{
+        u32 *pgdir, *linear;
+        unsigned int mapped_pages, i, linear_pages;
+        unsigned int ptes_per_page = getpagesize()/sizeof(u32);
+
+        /* If we can map all of memory above page_offset, we do so. */
+        if (mem <= -page_offset)
+                mapped_pages = mem/getpagesize();
+        else
+                mapped_pages = -page_offset/getpagesize();
+
+        /* Each linear PTE page can map ptes_per_page pages. */
+        linear_pages = (mapped_pages + ptes_per_page-1)/ptes_per_page;
+
+        /* We lay out top-level then linear mapping immediately below initrd */
+        pgdir = (void *)mem - initrd_size - getpagesize();
+        linear = (void *)pgdir - linear_pages*getpagesize();
+
+        for (i = 0; i < mapped_pages; i++)
+                linear[i] = ((i * getpagesize()) | PAGE_PRESENT);
+
+        /* Now set up pgd so that this memory is at page_offset */
+        for (i = 0; i < mapped_pages; i += ptes_per_page) {
+                pgdir[(i + page_offset/getpagesize())/ptes_per_page]
+                        = (((u32)linear + i*sizeof(u32)) | PAGE_PRESENT);
+        }
+
+        verbose("Linear mapping of %u pages in %u pte pages at %p\n",
+                mapped_pages, linear_pages, linear);
+
+        return (unsigned long)pgdir;
+}
+
+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';
+}
+
+static int tell_kernel(u32 pgdir, u32 start, u32 page_offset)
+{
+        u32 args[] = { LHREQ_INITIALIZE,
+                       LGUEST_GUEST_TOP/getpagesize(), /* Just below us */
+                       pgdir, start, page_offset };
+        int fd;
+
+        fd = open_or_die("/dev/lguest", O_RDWR);
+        if (write(fd, args, sizeof(args)) < 0)
+                err(1, "Writing to /dev/lguest");
+        return fd;
+}
+
+static void set_fd(int fd, struct device_list *devices)
+{
+        FD_SET(fd, &devices->infds);
+        if (fd > devices->max_infd)
+                devices->max_infd = fd;
+}
+
+/* When input arrives, we tell the kernel to kick lguest out with -EAGAIN. */
+static void wake_parent(int pipefd, int lguest_fd, struct device_list *devices)
+{
+        set_fd(pipefd, devices);
+
+        for (;;) {
+                fd_set rfds = devices->infds;
+                u32 args[] = { LHREQ_BREAK, 1 };
+
+                select(devices->max_infd+1, &rfds, NULL, NULL, NULL);
+                if (FD_ISSET(pipefd, &rfds)) {
+                        int ignorefd;
+                        if (read(pipefd, &ignorefd, sizeof(ignorefd)) == 0)
+                                exit(0);
+                        FD_CLR(ignorefd, &devices->infds);
+                } else
+                        write(lguest_fd, args, sizeof(args));
+        }
+}
+
+static int setup_waker(int lguest_fd, struct device_list *device_list)
+{
+        int pipefd[2], child;
+
+        pipe(pipefd);
+        child = fork();
+        if (child == -1)
+                err(1, "forking");
+
+        if (child == 0) {
+                close(pipefd[1]);
+                wake_parent(pipefd[0], lguest_fd, device_list);
+        }
+        close(pipefd[0]);
+
+        return pipefd[1];
+}
+
+static void *_check_pointer(unsigned long addr, unsigned int size,
+                            unsigned int line)
+{
+        if (addr >= LGUEST_GUEST_TOP || addr + size >= LGUEST_GUEST_TOP)
+                errx(1, "%s:%i: Invalid address %li", __FILE__, line, addr);
+        return (void *)addr;
+}
+#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
+
+/* Returns pointer to dma->used_len */
+static u32 *dma2iov(unsigned long dma, struct iovec iov[], unsigned *num)
+{
+        unsigned int i;
+        struct lguest_dma *udma;
+
+        udma = check_pointer(dma, sizeof(*udma));
+        for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
+                if (!udma->len[i])
+                        break;
+
+                iov[i].iov_base = check_pointer(udma->addr[i], udma->len[i]);
+                iov[i].iov_len = udma->len[i];
+        }
+        *num = i;
+        return &udma->used_len;
+}
+
+static u32 *get_dma_buffer(int fd, void *key,
+                           struct iovec iov[], unsigned int *num, u32 *irq)
+{
+        u32 buf[] = { LHREQ_GETDMA, (u32)key };
+        unsigned long udma;
+        u32 *res;
+
+        udma = write(fd, buf, sizeof(buf));
+        if (udma == (unsigned long)-1)
+                return NULL;
+
+        /* Kernel stashes irq in ->used_len. */
+        res = dma2iov(udma, iov, num);
+        *irq = *res;
+        return res;
+}
+
+static void trigger_irq(int fd, u32 irq)
+{
+        u32 buf[] = { LHREQ_IRQ, irq };
+        if (write(fd, buf, sizeof(buf)) != 0)
+                err(1, "Triggering irq %i", irq);
+}
+
+static void discard_iovec(struct iovec *iov, unsigned int *num)
+{
+        static char discard_buf[1024];
+        *num = 1;
+        iov->iov_base = discard_buf;
+        iov->iov_len = sizeof(discard_buf);
+}
+
+static struct termios orig_term;
+static void restore_term(void)
+{
+        tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
+}
+
+struct console_abort
+{
+        int count;
+        struct timeval start;
+};
+
+/* We DMA input to buffer bound at start of console page. */
+static bool handle_console_input(int fd, struct device *dev)
+{
+        u32 irq = 0, *lenp;
+        int len;
+        unsigned int num;
+        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
+        struct console_abort *abort = dev->priv;
+
+        lenp = get_dma_buffer(fd, dev->mem, iov, &num, &irq);
+        if (!lenp) {
+                warn("console: no dma buffer!");
+                discard_iovec(iov, &num);
+        }
+
+        len = readv(dev->fd, iov, num);
+        if (len <= 0) {
+                warnx("Failed to get console input, ignoring console.");
+                len = 0;
+        }
+
+        if (lenp) {
+                *lenp = len;
+                trigger_irq(fd, irq);
+        }
+
+        /* Three ^C within one second?  Exit. */
+        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) {
+                                /* Make sure waker is not blocked in BREAK */
+                                u32 args[] = { LHREQ_BREAK, 0 };
+                                close(waker_fd);
+                                write(fd, args, sizeof(args));
+                                exit(2);
+                        }
+                        abort->count = 0;
+                }
+        } else
+                abort->count = 0;
+
+        if (!len) {
+                restore_term();
+                return false;
+        }
+        return true;
+}
+
+static u32 handle_console_output(int fd, const struct iovec *iov,
+                                 unsigned num, struct device*dev)
+{
+        return writev(STDOUT_FILENO, iov, num);
+}
+
+static u32 handle_tun_output(int fd, const struct iovec *iov,
+                             unsigned num, struct device *dev)
+{
+        /* Now we've seen output, we should warn if we can't get buffers. */
+        *(bool *)dev->priv = true;
+        return writev(dev->fd, iov, num);
+}
+
+static unsigned long peer_offset(unsigned int peernum)
+{
+        return 4 * peernum;
+}
+
+static bool handle_tun_input(int fd, struct device *dev)
+{
+        u32 irq = 0, *lenp;
+        int len;
+        unsigned num;
+        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
+
+        lenp = get_dma_buffer(fd, dev->mem+peer_offset(NET_PEERNUM), iov, &num,
+                              &irq);
+        if (!lenp) {
+                if (*(bool *)dev->priv)
+                        warn("network: no dma buffer!");
+                discard_iovec(iov, &num);
+        }
+
+        len = readv(dev->fd, iov, num);
+        if (len <= 0)
+                err(1, "reading network");
+        if (lenp) {
+                *lenp = len;
+                trigger_irq(fd, irq);
+        }
+        verbose("tun input packet len %i [%02x %02x] (%s)\n", len,
+                ((u8 *)iov[0].iov_base)[0], ((u8 *)iov[0].iov_base)[1],
+                lenp ? "sent" : "discarded");
+        return true;
+}
+
+static u32 handle_block_output(int fd, const struct iovec *iov,
+                               unsigned num, struct device *dev)
+{
+        struct lguest_block_page *p = dev->mem;
+        u32 irq, *lenp;
+        unsigned int len, reply_num;
+        struct iovec reply[LGUEST_MAX_DMA_SECTIONS];
+        off64_t device_len, off = (off64_t)p->sector * 512;
+
+        device_len = *(off64_t *)dev->priv;
+
+        if (off >= device_len)
+                err(1, "Bad offset %llu vs %llu", off, device_len);
+        if (lseek64(dev->fd, off, SEEK_SET) != off)
+                err(1, "Bad seek to sector %i", p->sector);
+
+        verbose("Block: %s at offset %llu\n", p->type ? "WRITE" : "READ", off);
+
+        lenp = get_dma_buffer(fd, dev->mem, reply, &reply_num, &irq);
+        if (!lenp)
+                err(1, "Block request didn't give us a dma buffer");
+
+        if (p->type) {
+                len = writev(dev->fd, iov, num);
+                if (off + len > device_len) {
+                        ftruncate(dev->fd, device_len);
+                        errx(1, "Write past end %llu+%u", off, len);
+                }
+                *lenp = 0;
+        } else {
+                len = readv(dev->fd, reply, reply_num);
+                *lenp = len;
+        }
+
+        p->result = 1 + (p->bytes != len);
+        trigger_irq(fd, irq);
+        return 0;
+}
+
+static void handle_output(int fd, unsigned long dma, unsigned long key,
+                          struct device_list *devices)
+{
+        struct device *i;
+        u32 *lenp;
+        struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
+        unsigned num = 0;
+
+        lenp = dma2iov(dma, iov, &num);
+        for (i = devices->dev; i; i = i->next) {
+                if (i->handle_output && key == i->watch_key) {
+                        *lenp = i->handle_output(fd, iov, num, i);
+                        return;
+                }
+        }
+        warnx("Pending dma %p, key %p", (void *)dma, (void *)key);
+}
+
+static void handle_input(int fd, struct device_list *devices)
+{
+        struct timeval poll = { .tv_sec = 0, .tv_usec = 0 };
+
+        for (;;) {
+                struct device *i;
+                fd_set fds = devices->infds;
+
+                if (select(devices->max_infd+1, &fds, NULL, NULL, &poll) == 0)
+                        break;
+
+                for (i = devices->dev; i; i = i->next) {
+                        if (i->handle_input && FD_ISSET(i->fd, &fds)) {
+                                if (!i->handle_input(fd, i)) {
+                                        FD_CLR(i->fd, &devices->infds);
+                                        /* Tell waker to ignore it too... */
+                                        write(waker_fd, &i->fd, sizeof(i->fd));
+                                }
+                        }
+                }
+        }
+}
+
+static struct lguest_device_desc *new_dev_desc(u16 type, u16 features,
+                                               u16 num_pages)
+{
+        static unsigned long top = LGUEST_GUEST_TOP;
+        struct lguest_device_desc *desc;
+
+        desc = malloc(sizeof(*desc));
+        desc->type = type;
+        desc->num_pages = num_pages;
+        desc->features = features;
+        desc->status = 0;
+        if (num_pages) {
+                top -= num_pages*getpagesize();
+                map_zeroed_pages(top, num_pages);
+                desc->pfn = top / getpagesize();
+        } else
+                desc->pfn = 0;
+        return desc;
+}
+
+static struct device *new_device(struct device_list *devices,
+                                 u16 type, u16 num_pages, u16 features,
+                                 int fd,
+                                 bool (*handle_input)(int, struct device *),
+                                 unsigned long watch_off,
+                                 u32 (*handle_output)(int,
+                                                      const struct iovec *,
+                                                      unsigned,
+                                                      struct device *))
+{
+        struct device *dev = malloc(sizeof(*dev));
+
+        /* Append to device list. */
+        *devices->lastdev = dev;
+        dev->next = NULL;
+        devices->lastdev = &dev->next;
+
+        dev->fd = fd;
+        if (handle_input)
+                set_fd(dev->fd, devices);
+        dev->desc = new_dev_desc(type, features, num_pages);
+        dev->mem = (void *)(dev->desc->pfn * getpagesize());
+        dev->handle_input = handle_input;
+        dev->watch_key = (unsigned long)dev->mem + watch_off;
+        dev->handle_output = handle_output;
+        return dev;
+}
+
+static void setup_console(struct device_list *devices)
+{
+        struct device *dev;
+
+        if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
+                struct termios term = orig_term;
+                term.c_lflag &= ~(ISIG|ICANON|ECHO);
+                tcsetattr(STDIN_FILENO, TCSANOW, &term);
+                atexit(restore_term);
+        }
+
+        /* We don't currently require a page for the console. */
+        dev = new_device(devices, LGUEST_DEVICE_T_CONSOLE, 0, 0,
+                         STDIN_FILENO, handle_console_input,
+                         LGUEST_CONSOLE_DMA_KEY, handle_console_output);
+        dev->priv = malloc(sizeof(struct console_abort));
+        ((struct console_abort *)dev->priv)->count = 0;
+        verbose("device %p: console\n",
+                (void *)(dev->desc->pfn * getpagesize()));
+}
+
+static void setup_block_file(const char *filename, struct device_list *devices)
+{
+        int fd;
+        struct device *dev;
+        off64_t *device_len;
+        struct lguest_block_page *p;
+
+        fd = open_or_die(filename, O_RDWR|O_LARGEFILE|O_DIRECT);
+        dev = new_device(devices, LGUEST_DEVICE_T_BLOCK, 1,
+                         LGUEST_DEVICE_F_RANDOMNESS,
+                         fd, NULL, 0, handle_block_output);
+        device_len = dev->priv = malloc(sizeof(*device_len));
+        *device_len = lseek64(fd, 0, SEEK_END);
+        p = dev->mem;
+
+        p->num_sectors = *device_len/512;
+        verbose("device %p: block %i sectors\n",
+                (void *)(dev->desc->pfn * getpagesize()), p->num_sectors);
+}
+
+/* We use fnctl locks to reserve network slots (autocleanup!) */
+static unsigned int find_slot(int netfd, const char *filename)
+{
+        struct flock fl;
+
+        fl.l_type = F_WRLCK;
+        fl.l_whence = SEEK_SET;
+        fl.l_len = 1;
+        for (fl.l_start = 0;
+             fl.l_start < getpagesize()/sizeof(struct lguest_net);
+             fl.l_start++) {
+                if (fcntl(netfd, F_SETLK, &fl) == 0)
+                        return fl.l_start;
+        }
+        errx(1, "No free slots in network file %s", filename);
+}
+
+static void setup_net_file(const char *filename,
+                           struct device_list *devices)
+{
+        int netfd;
+        struct device *dev;
+
+        netfd = open(filename, O_RDWR, 0);
+        if (netfd < 0) {
+                if (errno == ENOENT) {
+                        netfd = open(filename, O_RDWR|O_CREAT, 0600);
+                        if (netfd >= 0) {
+                                char page[getpagesize()];
+                                memset(page, 0, sizeof(page));
+                                write(netfd, page, sizeof(page));
+                        }
+                }
+                if (netfd < 0)
+                        err(1, "cannot open net file '%s'", filename);
+        }
+
+        dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
+                         find_slot(netfd, filename)|LGUEST_NET_F_NOCSUM,
+                         -1, NULL, 0, NULL);
+
+        /* We overwrite the /dev/zero mapping with the actual file. */
+        if (mmap(dev->mem, getpagesize(), PROT_READ|PROT_WRITE,
+                         MAP_FIXED|MAP_SHARED, netfd, 0) != dev->mem)
+                        err(1, "could not mmap '%s'", filename);
+        verbose("device %p: shared net %s, peer %i\n",
+                (void *)(dev->desc->pfn * getpagesize()), filename,
+                dev->desc->features & ~LGUEST_NET_F_NOCSUM);
+}
+
+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];
+}
+
+/* adapted from libbridge */
+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);
+}
+
+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;
+
+        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);
+
+        if (ioctl(fd, SIOCGIFHWADDR, &ifr) != 0)
+                err(1, "getting hw address for %s", devname);
+
+        memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);
+}
+
+static void setup_tun_net(const char *arg, struct device_list *devices)
+{
+        struct device *dev;
+        struct ifreq ifr;
+        int netfd, ipfd;
+        u32 ip;
+        const char *br_name = NULL;
+
+        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");
+        ioctl(netfd, TUNSETNOCSUM, 1);
+
+        /* You will be peer 1: we should create enough jitter to randomize */
+        dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
+                         NET_PEERNUM|LGUEST_DEVICE_F_RANDOMNESS, netfd,
+                         handle_tun_input, peer_offset(0), handle_tun_output);
+        dev->priv = malloc(sizeof(bool));
+        *(bool *)dev->priv = false;
+
+        ipfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
+        if (ipfd < 0)
+                err(1, "opening IP socket");
+
+        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
+                ip = str2ip(arg);
+
+        /* We are peer 0, ie. first slot. */
+        configure_device(ipfd, ifr.ifr_name, ip, dev->mem);
+
+        /* Set "promisc" bit: we want every single packet. */
+        *((u8 *)dev->mem) |= 0x1;
+
+        close(ipfd);
+
+        verbose("device %p: tun net %u.%u.%u.%u\n",
+                (void *)(dev->desc->pfn * getpagesize()),
+                (u8)(ip>>24), (u8)(ip>>16), (u8)(ip>>8), (u8)ip);
+        if (br_name)
+                verbose("attached to bridge: %s\n", br_name);
+}
+
+/* Now we know how much memory we have, we copy in device descriptors */
+static void map_device_descriptors(struct device_list *devs, unsigned long mem)
+{
+        struct device *i;
+        unsigned int num;
+        struct lguest_device_desc *descs;
+
+        /* Device descriptor array sits just above top of normal memory */
+        descs = map_zeroed_pages(mem, 1);
+
+        for (i = devs->dev, num = 0; i; i = i->next, num++) {
+                if (num == LGUEST_MAX_DEVICES)
+                        errx(1, "too many devices");
+                verbose("Device %i: %s\n", num,
+                        i->desc->type == LGUEST_DEVICE_T_NET ? "net"
+                        : i->desc->type == LGUEST_DEVICE_T_CONSOLE ? "console"
+                        : i->desc->type == LGUEST_DEVICE_T_BLOCK ? "block"
+                        : "unknown");
+                descs[num] = *i->desc;
+                free(i->desc);
+                i->desc = &descs[num];
+        }
+}
+
+static void __attribute__((noreturn))
+run_guest(int lguest_fd, struct device_list *device_list)
+{
+        for (;;) {
+                u32 args[] = { LHREQ_BREAK, 0 };
+                unsigned long arr[2];
+                int readval;
+
+                /* We read from the /dev/lguest device to run the Guest. */
+                readval = read(lguest_fd, arr, sizeof(arr));
+
+                if (readval == sizeof(arr)) {
+                        handle_output(lguest_fd, arr[0], arr[1], device_list);
+                        continue;
+                } else if (errno == ENOENT) {
+                        char reason[1024] = { 0 };
+                        read(lguest_fd, reason, sizeof(reason)-1);
+                        errx(1, "%s", reason);
+                } else if (errno != EAGAIN)
+                        err(1, "Running guest failed");
+                handle_input(lguest_fd, device_list);
+                if (write(lguest_fd, args, sizeof(args)) < 0)
+                        err(1, "Resetting break");
+        }
+}
+
+static struct option opts[] = {
+        { "verbose", 0, NULL, 'v' },
+        { "sharenet", 1, NULL, 's' },
+        { "tunnet", 1, NULL, 't' },
+        { "block", 1, NULL, 'b' },
+        { "initrd", 1, NULL, 'i' },
+        { NULL },
+};
+static void usage(void)
+{
+        errx(1, "Usage: lguest [--verbose] "
+             "[--sharenet=<filename>|--tunnet=(<ipaddr>|bridge:<bridgename>)\n"
+             "|--block=<filename>|--initrd=<filename>]...\n"
+             "<mem-in-mb> vmlinux [args...]");
+}
+
+int main(int argc, char *argv[])
+{
+        unsigned long mem, pgdir, start, page_offset, initrd_size = 0;
+        int c, lguest_fd;
+        struct device_list device_list;
+        void *boot = (void *)0;
+        const char *initrd_name = NULL;
+
+        device_list.max_infd = -1;
+        device_list.dev = NULL;
+        device_list.lastdev = &device_list.dev;
+        FD_ZERO(&device_list.infds);
+
+        while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
+                switch (c) {
+                case 'v':
+                        verbose = true;
+                        break;
+                case 's':
+                        setup_net_file(optarg, &device_list);
+                        break;
+                case 't':
+                        setup_tun_net(optarg, &device_list);
+                        break;
+                case 'b':
+                        setup_block_file(optarg, &device_list);
+                        break;
+                case 'i':
+                        initrd_name = optarg;
+                        break;
+                default:
+                        warnx("Unknown argument %s", argv[optind]);
+                        usage();
+                }
+        }
+        if (optind + 2 > argc)
+                usage();
+
+        /* We need a console device */
+        setup_console(&device_list);
+
+        /* First we map /dev/zero over all of guest-physical memory. */
+        mem = atoi(argv[optind]) * 1024 * 1024;
+        map_zeroed_pages(0, mem / getpagesize());
+
+        /* Now we load the kernel */
+        start = load_kernel(open_or_die(argv[optind+1], O_RDONLY),
+                            &page_offset);
+
+        /* Write the device descriptors into memory. */
+        map_device_descriptors(&device_list, mem);
+
+        /* Map the initrd image if requested */
+        if (initrd_name) {
+                initrd_size = load_initrd(initrd_name, mem);
+                *(unsigned long *)(boot+0x218) = mem - initrd_size;
+                *(unsigned long *)(boot+0x21c) = initrd_size;
+                *(unsigned char *)(boot+0x210) = 0xFF;
+        }
+
+        /* Set up the initial linar pagetables. */
+        pgdir = setup_pagetables(mem, initrd_size, page_offset);
+
+        /* E820 memory map: ours is a simple, single region. */
+        *(char*)(boot+E820NR) = 1;
+        *((struct e820entry *)(boot+E820MAP))
+                = ((struct e820entry) { 0, mem, E820_RAM });
+        /* Command line pointer and command line (at 4096) */
+        *(void **)(boot + 0x228) = boot + 4096;
+        concat(boot + 4096, argv+optind+2);
+        /* Paravirt type: 1 == lguest */
+        *(int *)(boot + 0x23c) = 1;
+
+        lguest_fd = tell_kernel(pgdir, start, page_offset);
+        waker_fd = setup_waker(lguest_fd, &device_list);
+
+        run_guest(lguest_fd, &device_list);
+}