lguest: documentation I: Preparation

[deliverable/linux.git] / Documentation / lguest / 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.
 *
 * The only trick: the Makefile links it at a high address so it will be clear
 * of the guest memory region.  It means that each Guest cannot have more than
 * about 2.5G of memory on a normally configured Host. :*/
#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;
static u32 top;

struct device_list
{
        fd_set infds;
        int max_infd;

        struct lguest_device_desc *descs;
        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,
                       top/getpagesize(), 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 >= top || addr + size >= 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(struct lguest_device_desc *descs,
             u16 type, u16 features, u16 num_pages)
{
        unsigned int i;

        for (i = 0; i < LGUEST_MAX_DEVICES; i++) {
                if (!descs[i].type) {
                        descs[i].type = type;
                        descs[i].features = features;
                        descs[i].num_pages = num_pages;
                        if (num_pages) {
                                map_zeroed_pages(top, num_pages);
                                descs[i].pfn = top/getpagesize();
                                top += num_pages*getpagesize();
                        }
                        return &descs[i];
                }
        }
        errx(1, "too many devices");
}

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(devices->descs, 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);
}

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 = 0, pgdir, start, page_offset, initrd_size = 0;
        int i, 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);

        /* We need to know how much memory so we can allocate devices. */
        for (i = 1; i < argc; i++) {
                if (argv[i][0] != '-') {
                        mem = top = atoi(argv[i]) * 1024 * 1024;
                        device_list.descs = map_zeroed_pages(top, 1);
                        top += getpagesize();
                        break;
                }
        }
        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. */
        map_zeroed_pages(0, mem / getpagesize());

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

        /* 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);
}