linux/tools/lguest/lguest.c
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   1/*P:100
   2 * This is the Launcher code, a simple program which lays out the "physical"
   3 * memory for the new Guest by mapping the kernel image and the virtual
   4 * devices, then opens /dev/lguest to tell the kernel about the Guest and
   5 * control it.
   6:*/
   7#define _LARGEFILE64_SOURCE
   8#define _GNU_SOURCE
   9#include <stdio.h>
  10#include <string.h>
  11#include <unistd.h>
  12#include <err.h>
  13#include <stdint.h>
  14#include <stdlib.h>
  15#include <elf.h>
  16#include <sys/mman.h>
  17#include <sys/param.h>
  18#include <sys/types.h>
  19#include <sys/stat.h>
  20#include <sys/wait.h>
  21#include <sys/eventfd.h>
  22#include <fcntl.h>
  23#include <stdbool.h>
  24#include <errno.h>
  25#include <ctype.h>
  26#include <sys/socket.h>
  27#include <sys/ioctl.h>
  28#include <sys/time.h>
  29#include <time.h>
  30#include <netinet/in.h>
  31#include <net/if.h>
  32#include <linux/sockios.h>
  33#include <linux/if_tun.h>
  34#include <sys/uio.h>
  35#include <termios.h>
  36#include <getopt.h>
  37#include <assert.h>
  38#include <sched.h>
  39#include <limits.h>
  40#include <stddef.h>
  41#include <signal.h>
  42#include <pwd.h>
  43#include <grp.h>
  44
  45#include <linux/virtio_config.h>
  46#include <linux/virtio_net.h>
  47#include <linux/virtio_blk.h>
  48#include <linux/virtio_console.h>
  49#include <linux/virtio_rng.h>
  50#include <linux/virtio_ring.h>
  51#include <asm/bootparam.h>
  52#include "../../include/linux/lguest_launcher.h"
  53/*L:110
  54 * We can ignore the 43 include files we need for this program, but I do want
  55 * to draw attention to the use of kernel-style types.
  56 *
  57 * As Linus said, "C is a Spartan language, and so should your naming be."  I
  58 * like these abbreviations, so we define them here.  Note that u64 is always
  59 * unsigned long long, which works on all Linux systems: this means that we can
  60 * use %llu in printf for any u64.
  61 */
  62typedef unsigned long long u64;
  63typedef uint32_t u32;
  64typedef uint16_t u16;
  65typedef uint8_t u8;
  66/*:*/
  67
  68#define BRIDGE_PFX "bridge:"
  69#ifndef SIOCBRADDIF
  70#define SIOCBRADDIF     0x89a2          /* add interface to bridge      */
  71#endif
  72/* We can have up to 256 pages for devices. */
  73#define DEVICE_PAGES 256
  74/* This will occupy 3 pages: it must be a power of 2. */
  75#define VIRTQUEUE_NUM 256
  76
  77/*L:120
  78 * verbose is both a global flag and a macro.  The C preprocessor allows
  79 * this, and although I wouldn't recommend it, it works quite nicely here.
  80 */
  81static bool verbose;
  82#define verbose(args...) \
  83        do { if (verbose) printf(args); } while(0)
  84/*:*/
  85
  86/* The pointer to the start of guest memory. */
  87static void *guest_base;
  88/* The maximum guest physical address allowed, and maximum possible. */
  89static unsigned long guest_limit, guest_max;
  90/* The /dev/lguest file descriptor. */
  91static int lguest_fd;
  92
  93/* a per-cpu variable indicating whose vcpu is currently running */
  94static unsigned int __thread cpu_id;
  95
  96/* This is our list of devices. */
  97struct device_list {
  98        /* Counter to assign interrupt numbers. */
  99        unsigned int next_irq;
 100
 101        /* Counter to print out convenient device numbers. */
 102        unsigned int device_num;
 103
 104        /* The descriptor page for the devices. */
 105        u8 *descpage;
 106
 107        /* A single linked list of devices. */
 108        struct device *dev;
 109        /* And a pointer to the last device for easy append. */
 110        struct device *lastdev;
 111};
 112
 113/* The list of Guest devices, based on command line arguments. */
 114static struct device_list devices;
 115
 116/* The device structure describes a single device. */
 117struct device {
 118        /* The linked-list pointer. */
 119        struct device *next;
 120
 121        /* The device's descriptor, as mapped into the Guest. */
 122        struct lguest_device_desc *desc;
 123
 124        /* We can't trust desc values once Guest has booted: we use these. */
 125        unsigned int feature_len;
 126        unsigned int num_vq;
 127
 128        /* The name of this device, for --verbose. */
 129        const char *name;
 130
 131        /* Any queues attached to this device */
 132        struct virtqueue *vq;
 133
 134        /* Is it operational */
 135        bool running;
 136
 137        /* Device-specific data. */
 138        void *priv;
 139};
 140
 141/* The virtqueue structure describes a queue attached to a device. */
 142struct virtqueue {
 143        struct virtqueue *next;
 144
 145        /* Which device owns me. */
 146        struct device *dev;
 147
 148        /* The configuration for this queue. */
 149        struct lguest_vqconfig config;
 150
 151        /* The actual ring of buffers. */
 152        struct vring vring;
 153
 154        /* Last available index we saw. */
 155        u16 last_avail_idx;
 156
 157        /* How many are used since we sent last irq? */
 158        unsigned int pending_used;
 159
 160        /* Eventfd where Guest notifications arrive. */
 161        int eventfd;
 162
 163        /* Function for the thread which is servicing this virtqueue. */
 164        void (*service)(struct virtqueue *vq);
 165        pid_t thread;
 166};
 167
 168/* Remember the arguments to the program so we can "reboot" */
 169static char **main_args;
 170
 171/* The original tty settings to restore on exit. */
 172static struct termios orig_term;
 173
 174/*
 175 * We have to be careful with barriers: our devices are all run in separate
 176 * threads and so we need to make sure that changes visible to the Guest happen
 177 * in precise order.
 178 */
 179#define wmb() __asm__ __volatile__("" : : : "memory")
 180#define mb() __asm__ __volatile__("" : : : "memory")
 181
 182/*
 183 * Convert an iovec element to the given type.
 184 *
 185 * This is a fairly ugly trick: we need to know the size of the type and
 186 * alignment requirement to check the pointer is kosher.  It's also nice to
 187 * have the name of the type in case we report failure.
 188 *
 189 * Typing those three things all the time is cumbersome and error prone, so we
 190 * have a macro which sets them all up and passes to the real function.
 191 */
 192#define convert(iov, type) \
 193        ((type *)_convert((iov), sizeof(type), __alignof__(type), #type))
 194
 195static void *_convert(struct iovec *iov, size_t size, size_t align,
 196                      const char *name)
 197{
 198        if (iov->iov_len != size)
 199                errx(1, "Bad iovec size %zu for %s", iov->iov_len, name);
 200        if ((unsigned long)iov->iov_base % align != 0)
 201                errx(1, "Bad alignment %p for %s", iov->iov_base, name);
 202        return iov->iov_base;
 203}
 204
 205/* Wrapper for the last available index.  Makes it easier to change. */
 206#define lg_last_avail(vq)       ((vq)->last_avail_idx)
 207
 208/*
 209 * The virtio configuration space is defined to be little-endian.  x86 is
 210 * little-endian too, but it's nice to be explicit so we have these helpers.
 211 */
 212#define cpu_to_le16(v16) (v16)
 213#define cpu_to_le32(v32) (v32)
 214#define cpu_to_le64(v64) (v64)
 215#define le16_to_cpu(v16) (v16)
 216#define le32_to_cpu(v32) (v32)
 217#define le64_to_cpu(v64) (v64)
 218
 219/* Is this iovec empty? */
 220static bool iov_empty(const struct iovec iov[], unsigned int num_iov)
 221{
 222        unsigned int i;
 223
 224        for (i = 0; i < num_iov; i++)
 225                if (iov[i].iov_len)
 226                        return false;
 227        return true;
 228}
 229
 230/* Take len bytes from the front of this iovec. */
 231static void iov_consume(struct iovec iov[], unsigned num_iov, unsigned len)
 232{
 233        unsigned int i;
 234
 235        for (i = 0; i < num_iov; i++) {
 236                unsigned int used;
 237
 238                used = iov[i].iov_len < len ? iov[i].iov_len : len;
 239                iov[i].iov_base += used;
 240                iov[i].iov_len -= used;
 241                len -= used;
 242        }
 243        assert(len == 0);
 244}
 245
 246/* The device virtqueue descriptors are followed by feature bitmasks. */
 247static u8 *get_feature_bits(struct device *dev)
 248{
 249        return (u8 *)(dev->desc + 1)
 250                + dev->num_vq * sizeof(struct lguest_vqconfig);
 251}
 252
 253/*L:100
 254 * The Launcher code itself takes us out into userspace, that scary place where
 255 * pointers run wild and free!  Unfortunately, like most userspace programs,
 256 * it's quite boring (which is why everyone likes to hack on the kernel!).
 257 * Perhaps if you make up an Lguest Drinking Game at this point, it will get
 258 * you through this section.  Or, maybe not.
 259 *
 260 * The Launcher sets up a big chunk of memory to be the Guest's "physical"
 261 * memory and stores it in "guest_base".  In other words, Guest physical ==
 262 * Launcher virtual with an offset.
 263 *
 264 * This can be tough to get your head around, but usually it just means that we
 265 * use these trivial conversion functions when the Guest gives us its
 266 * "physical" addresses:
 267 */
 268static void *from_guest_phys(unsigned long addr)
 269{
 270        return guest_base + addr;
 271}
 272
 273static unsigned long to_guest_phys(const void *addr)
 274{
 275        return (addr - guest_base);
 276}
 277
 278/*L:130
 279 * Loading the Kernel.
 280 *
 281 * We start with couple of simple helper routines.  open_or_die() avoids
 282 * error-checking code cluttering the callers:
 283 */
 284static int open_or_die(const char *name, int flags)
 285{
 286        int fd = open(name, flags);
 287        if (fd < 0)
 288                err(1, "Failed to open %s", name);
 289        return fd;
 290}
 291
 292/* map_zeroed_pages() takes a number of pages. */
 293static void *map_zeroed_pages(unsigned int num)
 294{
 295        int fd = open_or_die("/dev/zero", O_RDONLY);
 296        void *addr;
 297
 298        /*
 299         * We use a private mapping (ie. if we write to the page, it will be
 300         * copied). We allocate an extra two pages PROT_NONE to act as guard
 301         * pages against read/write attempts that exceed allocated space.
 302         */
 303        addr = mmap(NULL, getpagesize() * (num+2),
 304                    PROT_NONE, MAP_PRIVATE, fd, 0);
 305
 306        if (addr == MAP_FAILED)
 307                err(1, "Mmapping %u pages of /dev/zero", num);
 308
 309        if (mprotect(addr + getpagesize(), getpagesize() * num,
 310                     PROT_READ|PROT_WRITE) == -1)
 311                err(1, "mprotect rw %u pages failed", num);
 312
 313        /*
 314         * One neat mmap feature is that you can close the fd, and it
 315         * stays mapped.
 316         */
 317        close(fd);
 318
 319        /* Return address after PROT_NONE page */
 320        return addr + getpagesize();
 321}
 322
 323/* Get some more pages for a device. */
 324static void *get_pages(unsigned int num)
 325{
 326        void *addr = from_guest_phys(guest_limit);
 327
 328        guest_limit += num * getpagesize();
 329        if (guest_limit > guest_max)
 330                errx(1, "Not enough memory for devices");
 331        return addr;
 332}
 333
 334/*
 335 * This routine is used to load the kernel or initrd.  It tries mmap, but if
 336 * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
 337 * it falls back to reading the memory in.
 338 */
 339static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
 340{
 341        ssize_t r;
 342
 343        /*
 344         * We map writable even though for some segments are marked read-only.
 345         * The kernel really wants to be writable: it patches its own
 346         * instructions.
 347         *
 348         * MAP_PRIVATE means that the page won't be copied until a write is
 349         * done to it.  This allows us to share untouched memory between
 350         * Guests.
 351         */
 352        if (mmap(addr, len, PROT_READ|PROT_WRITE,
 353                 MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
 354                return;
 355
 356        /* pread does a seek and a read in one shot: saves a few lines. */
 357        r = pread(fd, addr, len, offset);
 358        if (r != len)
 359                err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
 360}
 361
 362/*
 363 * This routine takes an open vmlinux image, which is in ELF, and maps it into
 364 * the Guest memory.  ELF = Embedded Linking Format, which is the format used
 365 * by all modern binaries on Linux including the kernel.
 366 *
 367 * The ELF headers give *two* addresses: a physical address, and a virtual
 368 * address.  We use the physical address; the Guest will map itself to the
 369 * virtual address.
 370 *
 371 * We return the starting address.
 372 */
 373static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
 374{
 375        Elf32_Phdr phdr[ehdr->e_phnum];
 376        unsigned int i;
 377
 378        /*
 379         * Sanity checks on the main ELF header: an x86 executable with a
 380         * reasonable number of correctly-sized program headers.
 381         */
 382        if (ehdr->e_type != ET_EXEC
 383            || ehdr->e_machine != EM_386
 384            || ehdr->e_phentsize != sizeof(Elf32_Phdr)
 385            || ehdr->e_phnum < 1 || ehdr->e_phnum > 65536U/sizeof(Elf32_Phdr))
 386                errx(1, "Malformed elf header");
 387
 388        /*
 389         * An ELF executable contains an ELF header and a number of "program"
 390         * headers which indicate which parts ("segments") of the program to
 391         * load where.
 392         */
 393
 394        /* We read in all the program headers at once: */
 395        if (lseek(elf_fd, ehdr->e_phoff, SEEK_SET) < 0)
 396                err(1, "Seeking to program headers");
 397        if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
 398                err(1, "Reading program headers");
 399
 400        /*
 401         * Try all the headers: there are usually only three.  A read-only one,
 402         * a read-write one, and a "note" section which we don't load.
 403         */
 404        for (i = 0; i < ehdr->e_phnum; i++) {
 405                /* If this isn't a loadable segment, we ignore it */
 406                if (phdr[i].p_type != PT_LOAD)
 407                        continue;
 408
 409                verbose("Section %i: size %i addr %p\n",
 410                        i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
 411
 412                /* We map this section of the file at its physical address. */
 413                map_at(elf_fd, from_guest_phys(phdr[i].p_paddr),
 414                       phdr[i].p_offset, phdr[i].p_filesz);
 415        }
 416
 417        /* The entry point is given in the ELF header. */
 418        return ehdr->e_entry;
 419}
 420
 421/*L:150
 422 * A bzImage, unlike an ELF file, is not meant to be loaded.  You're supposed
 423 * to jump into it and it will unpack itself.  We used to have to perform some
 424 * hairy magic because the unpacking code scared me.
 425 *
 426 * Fortunately, Jeremy Fitzhardinge convinced me it wasn't that hard and wrote
 427 * a small patch to jump over the tricky bits in the Guest, so now we just read
 428 * the funky header so we know where in the file to load, and away we go!
 429 */
 430static unsigned long load_bzimage(int fd)
 431{
 432        struct boot_params boot;
 433        int r;
 434        /* Modern bzImages get loaded at 1M. */
 435        void *p = from_guest_phys(0x100000);
 436
 437        /*
 438         * Go back to the start of the file and read the header.  It should be
 439         * a Linux boot header (see Documentation/x86/boot.txt)
 440         */
 441        lseek(fd, 0, SEEK_SET);
 442        read(fd, &boot, sizeof(boot));
 443
 444        /* Inside the setup_hdr, we expect the magic "HdrS" */
 445        if (memcmp(&boot.hdr.header, "HdrS", 4) != 0)
 446                errx(1, "This doesn't look like a bzImage to me");
 447
 448        /* Skip over the extra sectors of the header. */
 449        lseek(fd, (boot.hdr.setup_sects+1) * 512, SEEK_SET);
 450
 451        /* Now read everything into memory. in nice big chunks. */
 452        while ((r = read(fd, p, 65536)) > 0)
 453                p += r;
 454
 455        /* Finally, code32_start tells us where to enter the kernel. */
 456        return boot.hdr.code32_start;
 457}
 458
 459/*L:140
 460 * Loading the kernel is easy when it's a "vmlinux", but most kernels
 461 * come wrapped up in the self-decompressing "bzImage" format.  With a little
 462 * work, we can load those, too.
 463 */
 464static unsigned long load_kernel(int fd)
 465{
 466        Elf32_Ehdr hdr;
 467
 468        /* Read in the first few bytes. */
 469        if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
 470                err(1, "Reading kernel");
 471
 472        /* If it's an ELF file, it starts with "\177ELF" */
 473        if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
 474                return map_elf(fd, &hdr);
 475
 476        /* Otherwise we assume it's a bzImage, and try to load it. */
 477        return load_bzimage(fd);
 478}
 479
 480/*
 481 * This is a trivial little helper to align pages.  Andi Kleen hated it because
 482 * it calls getpagesize() twice: "it's dumb code."
 483 *
 484 * Kernel guys get really het up about optimization, even when it's not
 485 * necessary.  I leave this code as a reaction against that.
 486 */
 487static inline unsigned long page_align(unsigned long addr)
 488{
 489        /* Add upwards and truncate downwards. */
 490        return ((addr + getpagesize()-1) & ~(getpagesize()-1));
 491}
 492
 493/*L:180
 494 * An "initial ram disk" is a disk image loaded into memory along with the
 495 * kernel which the kernel can use to boot from without needing any drivers.
 496 * Most distributions now use this as standard: the initrd contains the code to
 497 * load the appropriate driver modules for the current machine.
 498 *
 499 * Importantly, James Morris works for RedHat, and Fedora uses initrds for its
 500 * kernels.  He sent me this (and tells me when I break it).
 501 */
 502static unsigned long load_initrd(const char *name, unsigned long mem)
 503{
 504        int ifd;
 505        struct stat st;
 506        unsigned long len;
 507
 508        ifd = open_or_die(name, O_RDONLY);
 509        /* fstat() is needed to get the file size. */
 510        if (fstat(ifd, &st) < 0)
 511                err(1, "fstat() on initrd '%s'", name);
 512
 513        /*
 514         * We map the initrd at the top of memory, but mmap wants it to be
 515         * page-aligned, so we round the size up for that.
 516         */
 517        len = page_align(st.st_size);
 518        map_at(ifd, from_guest_phys(mem - len), 0, st.st_size);
 519        /*
 520         * Once a file is mapped, you can close the file descriptor.  It's a
 521         * little odd, but quite useful.
 522         */
 523        close(ifd);
 524        verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);
 525
 526        /* We return the initrd size. */
 527        return len;
 528}
 529/*:*/
 530
 531/*
 532 * Simple routine to roll all the commandline arguments together with spaces
 533 * between them.
 534 */
 535static void concat(char *dst, char *args[])
 536{
 537        unsigned int i, len = 0;
 538
 539        for (i = 0; args[i]; i++) {
 540                if (i) {
 541                        strcat(dst+len, " ");
 542                        len++;
 543                }
 544                strcpy(dst+len, args[i]);
 545                len += strlen(args[i]);
 546        }
 547        /* In case it's empty. */
 548        dst[len] = '\0';
 549}
 550
 551/*L:185
 552 * This is where we actually tell the kernel to initialize the Guest.  We
 553 * saw the arguments it expects when we looked at initialize() in lguest_user.c:
 554 * the base of Guest "physical" memory, the top physical page to allow and the
 555 * entry point for the Guest.
 556 */
 557static void tell_kernel(unsigned long start)
 558{
 559        unsigned long args[] = { LHREQ_INITIALIZE,
 560                                 (unsigned long)guest_base,
 561                                 guest_limit / getpagesize(), start };
 562        verbose("Guest: %p - %p (%#lx)\n",
 563                guest_base, guest_base + guest_limit, guest_limit);
 564        lguest_fd = open_or_die("/dev/lguest", O_RDWR);
 565        if (write(lguest_fd, args, sizeof(args)) < 0)
 566                err(1, "Writing to /dev/lguest");
 567}
 568/*:*/
 569
 570/*L:200
 571 * Device Handling.
 572 *
 573 * When the Guest gives us a buffer, it sends an array of addresses and sizes.
 574 * We need to make sure it's not trying to reach into the Launcher itself, so
 575 * we have a convenient routine which checks it and exits with an error message
 576 * if something funny is going on:
 577 */
 578static void *_check_pointer(unsigned long addr, unsigned int size,
 579                            unsigned int line)
 580{
 581        /*
 582         * Check if the requested address and size exceeds the allocated memory,
 583         * or addr + size wraps around.
 584         */
 585        if ((addr + size) > guest_limit || (addr + size) < addr)
 586                errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
 587        /*
 588         * We return a pointer for the caller's convenience, now we know it's
 589         * safe to use.
 590         */
 591        return from_guest_phys(addr);
 592}
 593/* A macro which transparently hands the line number to the real function. */
 594#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
 595
 596/*
 597 * Each buffer in the virtqueues is actually a chain of descriptors.  This
 598 * function returns the next descriptor in the chain, or vq->vring.num if we're
 599 * at the end.
 600 */
 601static unsigned next_desc(struct vring_desc *desc,
 602                          unsigned int i, unsigned int max)
 603{
 604        unsigned int next;
 605
 606        /* If this descriptor says it doesn't chain, we're done. */
 607        if (!(desc[i].flags & VRING_DESC_F_NEXT))
 608                return max;
 609
 610        /* Check they're not leading us off end of descriptors. */
 611        next = desc[i].next;
 612        /* Make sure compiler knows to grab that: we don't want it changing! */
 613        wmb();
 614
 615        if (next >= max)
 616                errx(1, "Desc next is %u", next);
 617
 618        return next;
 619}
 620
 621/*
 622 * This actually sends the interrupt for this virtqueue, if we've used a
 623 * buffer.
 624 */
 625static void trigger_irq(struct virtqueue *vq)
 626{
 627        unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
 628
 629        /* Don't inform them if nothing used. */
 630        if (!vq->pending_used)
 631                return;
 632        vq->pending_used = 0;
 633
 634        /* If they don't want an interrupt, don't send one... */
 635        if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT) {
 636                return;
 637        }
 638
 639        /* Send the Guest an interrupt tell them we used something up. */
 640        if (write(lguest_fd, buf, sizeof(buf)) != 0)
 641                err(1, "Triggering irq %i", vq->config.irq);
 642}
 643
 644/*
 645 * This looks in the virtqueue for the first available buffer, and converts
 646 * it to an iovec for convenient access.  Since descriptors consist of some
 647 * number of output then some number of input descriptors, it's actually two
 648 * iovecs, but we pack them into one and note how many of each there were.
 649 *
 650 * This function waits if necessary, and returns the descriptor number found.
 651 */
 652static unsigned wait_for_vq_desc(struct virtqueue *vq,
 653                                 struct iovec iov[],
 654                                 unsigned int *out_num, unsigned int *in_num)
 655{
 656        unsigned int i, head, max;
 657        struct vring_desc *desc;
 658        u16 last_avail = lg_last_avail(vq);
 659
 660        /* There's nothing available? */
 661        while (last_avail == vq->vring.avail->idx) {
 662                u64 event;
 663
 664                /*
 665                 * Since we're about to sleep, now is a good time to tell the
 666                 * Guest about what we've used up to now.
 667                 */
 668                trigger_irq(vq);
 669
 670                /* OK, now we need to know about added descriptors. */
 671                vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;
 672
 673                /*
 674                 * They could have slipped one in as we were doing that: make
 675                 * sure it's written, then check again.
 676                 */
 677                mb();
 678                if (last_avail != vq->vring.avail->idx) {
 679                        vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
 680                        break;
 681                }
 682
 683                /* Nothing new?  Wait for eventfd to tell us they refilled. */
 684                if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event))
 685                        errx(1, "Event read failed?");
 686
 687                /* We don't need to be notified again. */
 688                vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
 689        }
 690
 691        /* Check it isn't doing very strange things with descriptor numbers. */
 692        if ((u16)(vq->vring.avail->idx - last_avail) > vq->vring.num)
 693                errx(1, "Guest moved used index from %u to %u",
 694                     last_avail, vq->vring.avail->idx);
 695
 696        /*
 697         * Grab the next descriptor number they're advertising, and increment
 698         * the index we've seen.
 699         */
 700        head = vq->vring.avail->ring[last_avail % vq->vring.num];
 701        lg_last_avail(vq)++;
 702
 703        /* If their number is silly, that's a fatal mistake. */
 704        if (head >= vq->vring.num)
 705                errx(1, "Guest says index %u is available", head);
 706
 707        /* When we start there are none of either input nor output. */
 708        *out_num = *in_num = 0;
 709
 710        max = vq->vring.num;
 711        desc = vq->vring.desc;
 712        i = head;
 713
 714        /*
 715         * If this is an indirect entry, then this buffer contains a descriptor
 716         * table which we handle as if it's any normal descriptor chain.
 717         */
 718        if (desc[i].flags & VRING_DESC_F_INDIRECT) {
 719                if (desc[i].len % sizeof(struct vring_desc))
 720                        errx(1, "Invalid size for indirect buffer table");
 721
 722                max = desc[i].len / sizeof(struct vring_desc);
 723                desc = check_pointer(desc[i].addr, desc[i].len);
 724                i = 0;
 725        }
 726
 727        do {
 728                /* Grab the first descriptor, and check it's OK. */
 729                iov[*out_num + *in_num].iov_len = desc[i].len;
 730                iov[*out_num + *in_num].iov_base
 731                        = check_pointer(desc[i].addr, desc[i].len);
 732                /* If this is an input descriptor, increment that count. */
 733                if (desc[i].flags & VRING_DESC_F_WRITE)
 734                        (*in_num)++;
 735                else {
 736                        /*
 737                         * If it's an output descriptor, they're all supposed
 738                         * to come before any input descriptors.
 739                         */
 740                        if (*in_num)
 741                                errx(1, "Descriptor has out after in");
 742                        (*out_num)++;
 743                }
 744
 745                /* If we've got too many, that implies a descriptor loop. */
 746                if (*out_num + *in_num > max)
 747                        errx(1, "Looped descriptor");
 748        } while ((i = next_desc(desc, i, max)) != max);
 749
 750        return head;
 751}
 752
 753/*
 754 * After we've used one of their buffers, we tell the Guest about it.  Sometime
 755 * later we'll want to send them an interrupt using trigger_irq(); note that
 756 * wait_for_vq_desc() does that for us if it has to wait.
 757 */
 758static void add_used(struct virtqueue *vq, unsigned int head, int len)
 759{
 760        struct vring_used_elem *used;
 761
 762        /*
 763         * The virtqueue contains a ring of used buffers.  Get a pointer to the
 764         * next entry in that used ring.
 765         */
 766        used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
 767        used->id = head;
 768        used->len = len;
 769        /* Make sure buffer is written before we update index. */
 770        wmb();
 771        vq->vring.used->idx++;
 772        vq->pending_used++;
 773}
 774
 775/* And here's the combo meal deal.  Supersize me! */
 776static void add_used_and_trigger(struct virtqueue *vq, unsigned head, int len)
 777{
 778        add_used(vq, head, len);
 779        trigger_irq(vq);
 780}
 781
 782/*
 783 * The Console
 784 *
 785 * We associate some data with the console for our exit hack.
 786 */
 787struct console_abort {
 788        /* How many times have they hit ^C? */
 789        int count;
 790        /* When did they start? */
 791        struct timeval start;
 792};
 793
 794/* This is the routine which handles console input (ie. stdin). */
 795static void console_input(struct virtqueue *vq)
 796{
 797        int len;
 798        unsigned int head, in_num, out_num;
 799        struct console_abort *abort = vq->dev->priv;
 800        struct iovec iov[vq->vring.num];
 801
 802        /* Make sure there's a descriptor available. */
 803        head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
 804        if (out_num)
 805                errx(1, "Output buffers in console in queue?");
 806
 807        /* Read into it.  This is where we usually wait. */
 808        len = readv(STDIN_FILENO, iov, in_num);
 809        if (len <= 0) {
 810                /* Ran out of input? */
 811                warnx("Failed to get console input, ignoring console.");
 812                /*
 813                 * For simplicity, dying threads kill the whole Launcher.  So
 814                 * just nap here.
 815                 */
 816                for (;;)
 817                        pause();
 818        }
 819
 820        /* Tell the Guest we used a buffer. */
 821        add_used_and_trigger(vq, head, len);
 822
 823        /*
 824         * Three ^C within one second?  Exit.
 825         *
 826         * This is such a hack, but works surprisingly well.  Each ^C has to
 827         * be in a buffer by itself, so they can't be too fast.  But we check
 828         * that we get three within about a second, so they can't be too
 829         * slow.
 830         */
 831        if (len != 1 || ((char *)iov[0].iov_base)[0] != 3) {
 832                abort->count = 0;
 833                return;
 834        }
 835
 836        abort->count++;
 837        if (abort->count == 1)
 838                gettimeofday(&abort->start, NULL);
 839        else if (abort->count == 3) {
 840                struct timeval now;
 841                gettimeofday(&now, NULL);
 842                /* Kill all Launcher processes with SIGINT, like normal ^C */
 843                if (now.tv_sec <= abort->start.tv_sec+1)
 844                        kill(0, SIGINT);
 845                abort->count = 0;
 846        }
 847}
 848
 849/* This is the routine which handles console output (ie. stdout). */
 850static void console_output(struct virtqueue *vq)
 851{
 852        unsigned int head, out, in;
 853        struct iovec iov[vq->vring.num];
 854
 855        /* We usually wait in here, for the Guest to give us something. */
 856        head = wait_for_vq_desc(vq, iov, &out, &in);
 857        if (in)
 858                errx(1, "Input buffers in console output queue?");
 859
 860        /* writev can return a partial write, so we loop here. */
 861        while (!iov_empty(iov, out)) {
 862                int len = writev(STDOUT_FILENO, iov, out);
 863                if (len <= 0) {
 864                        warn("Write to stdout gave %i (%d)", len, errno);
 865                        break;
 866                }
 867                iov_consume(iov, out, len);
 868        }
 869
 870        /*
 871         * We're finished with that buffer: if we're going to sleep,
 872         * wait_for_vq_desc() will prod the Guest with an interrupt.
 873         */
 874        add_used(vq, head, 0);
 875}
 876
 877/*
 878 * The Network
 879 *
 880 * Handling output for network is also simple: we get all the output buffers
 881 * and write them to /dev/net/tun.
 882 */
 883struct net_info {
 884        int tunfd;
 885};
 886
 887static void net_output(struct virtqueue *vq)
 888{
 889        struct net_info *net_info = vq->dev->priv;
 890        unsigned int head, out, in;
 891        struct iovec iov[vq->vring.num];
 892
 893        /* We usually wait in here for the Guest to give us a packet. */
 894        head = wait_for_vq_desc(vq, iov, &out, &in);
 895        if (in)
 896                errx(1, "Input buffers in net output queue?");
 897        /*
 898         * Send the whole thing through to /dev/net/tun.  It expects the exact
 899         * same format: what a coincidence!
 900         */
 901        if (writev(net_info->tunfd, iov, out) < 0)
 902                warnx("Write to tun failed (%d)?", errno);
 903
 904        /*
 905         * Done with that one; wait_for_vq_desc() will send the interrupt if
 906         * all packets are processed.
 907         */
 908        add_used(vq, head, 0);
 909}
 910
 911/*
 912 * Handling network input is a bit trickier, because I've tried to optimize it.
 913 *
 914 * First we have a helper routine which tells is if from this file descriptor
 915 * (ie. the /dev/net/tun device) will block:
 916 */
 917static bool will_block(int fd)
 918{
 919        fd_set fdset;
 920        struct timeval zero = { 0, 0 };
 921        FD_ZERO(&fdset);
 922        FD_SET(fd, &fdset);
 923        return select(fd+1, &fdset, NULL, NULL, &zero) != 1;
 924}
 925
 926/*
 927 * This handles packets coming in from the tun device to our Guest.  Like all
 928 * service routines, it gets called again as soon as it returns, so you don't
 929 * see a while(1) loop here.
 930 */
 931static void net_input(struct virtqueue *vq)
 932{
 933        int len;
 934        unsigned int head, out, in;
 935        struct iovec iov[vq->vring.num];
 936        struct net_info *net_info = vq->dev->priv;
 937
 938        /*
 939         * Get a descriptor to write an incoming packet into.  This will also
 940         * send an interrupt if they're out of descriptors.
 941         */
 942        head = wait_for_vq_desc(vq, iov, &out, &in);
 943        if (out)
 944                errx(1, "Output buffers in net input queue?");
 945
 946        /*
 947         * If it looks like we'll block reading from the tun device, send them
 948         * an interrupt.
 949         */
 950        if (vq->pending_used && will_block(net_info->tunfd))
 951                trigger_irq(vq);
 952
 953        /*
 954         * Read in the packet.  This is where we normally wait (when there's no
 955         * incoming network traffic).
 956         */
 957        len = readv(net_info->tunfd, iov, in);
 958        if (len <= 0)
 959                warn("Failed to read from tun (%d).", errno);
 960
 961        /*
 962         * Mark that packet buffer as used, but don't interrupt here.  We want
 963         * to wait until we've done as much work as we can.
 964         */
 965        add_used(vq, head, len);
 966}
 967/*:*/
 968
 969/* This is the helper to create threads: run the service routine in a loop. */
 970static int do_thread(void *_vq)
 971{
 972        struct virtqueue *vq = _vq;
 973
 974        for (;;)
 975                vq->service(vq);
 976        return 0;
 977}
 978
 979/*
 980 * When a child dies, we kill our entire process group with SIGTERM.  This
 981 * also has the side effect that the shell restores the console for us!
 982 */
 983static void kill_launcher(int signal)
 984{
 985        kill(0, SIGTERM);
 986}
 987
 988static void reset_device(struct device *dev)
 989{
 990        struct virtqueue *vq;
 991
 992        verbose("Resetting device %s\n", dev->name);
 993
 994        /* Clear any features they've acked. */
 995        memset(get_feature_bits(dev) + dev->feature_len, 0, dev->feature_len);
 996
 997        /* We're going to be explicitly killing threads, so ignore them. */
 998        signal(SIGCHLD, SIG_IGN);
 999
1000        /* Zero out the virtqueues, get rid of their threads */
1001        for (vq = dev->vq; vq; vq = vq->next) {
1002                if (vq->thread != (pid_t)-1) {
1003                        kill(vq->thread, SIGTERM);
1004                        waitpid(vq->thread, NULL, 0);
1005                        vq->thread = (pid_t)-1;
1006                }
1007                memset(vq->vring.desc, 0,
1008                       vring_size(vq->config.num, LGUEST_VRING_ALIGN));
1009                lg_last_avail(vq) = 0;
1010        }
1011        dev->running = false;
1012
1013        /* Now we care if threads die. */
1014        signal(SIGCHLD, (void *)kill_launcher);
1015}
1016
1017/*L:216
1018 * This actually creates the thread which services the virtqueue for a device.
1019 */
1020static void create_thread(struct virtqueue *vq)
1021{
1022        /*
1023         * Create stack for thread.  Since the stack grows upwards, we point
1024         * the stack pointer to the end of this region.
1025         */
1026        char *stack = malloc(32768);
1027        unsigned long args[] = { LHREQ_EVENTFD,
1028                                 vq->config.pfn*getpagesize(), 0 };
1029
1030        /* Create a zero-initialized eventfd. */
1031        vq->eventfd = eventfd(0, 0);
1032        if (vq->eventfd < 0)
1033                err(1, "Creating eventfd");
1034        args[2] = vq->eventfd;
1035
1036        /*
1037         * Attach an eventfd to this virtqueue: it will go off when the Guest
1038         * does an LHCALL_NOTIFY for this vq.
1039         */
1040        if (write(lguest_fd, &args, sizeof(args)) != 0)
1041                err(1, "Attaching eventfd");
1042
1043        /*
1044         * CLONE_VM: because it has to access the Guest memory, and SIGCHLD so
1045         * we get a signal if it dies.
1046         */
1047        vq->thread = clone(do_thread, stack + 32768, CLONE_VM | SIGCHLD, vq);
1048        if (vq->thread == (pid_t)-1)
1049                err(1, "Creating clone");
1050
1051        /* We close our local copy now the child has it. */
1052        close(vq->eventfd);
1053}
1054
1055static void start_device(struct device *dev)
1056{
1057        unsigned int i;
1058        struct virtqueue *vq;
1059
1060        verbose("Device %s OK: offered", dev->name);
1061        for (i = 0; i < dev->feature_len; i++)
1062                verbose(" %02x", get_feature_bits(dev)[i]);
1063        verbose(", accepted");
1064        for (i = 0; i < dev->feature_len; i++)
1065                verbose(" %02x", get_feature_bits(dev)
1066                        [dev->feature_len+i]);
1067
1068        for (vq = dev->vq; vq; vq = vq->next) {
1069                if (vq->service)
1070                        create_thread(vq);
1071        }
1072        dev->running = true;
1073}
1074
1075static void cleanup_devices(void)
1076{
1077        struct device *dev;
1078
1079        for (dev = devices.dev; dev; dev = dev->next)
1080                reset_device(dev);
1081
1082        /* If we saved off the original terminal settings, restore them now. */
1083        if (orig_term.c_lflag & (ISIG|ICANON|ECHO))
1084                tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
1085}
1086
1087/* When the Guest tells us they updated the status field, we handle it. */
1088static void update_device_status(struct device *dev)
1089{
1090        /* A zero status is a reset, otherwise it's a set of flags. */
1091        if (dev->desc->status == 0)
1092                reset_device(dev);
1093        else if (dev->desc->status & VIRTIO_CONFIG_S_FAILED) {
1094                warnx("Device %s configuration FAILED", dev->name);
1095                if (dev->running)
1096                        reset_device(dev);
1097        } else {
1098                if (dev->running)
1099                        err(1, "Device %s features finalized twice", dev->name);
1100                start_device(dev);
1101        }
1102}
1103
1104/*L:215
1105 * This is the generic routine we call when the Guest uses LHCALL_NOTIFY.  In
1106 * particular, it's used to notify us of device status changes during boot.
1107 */
1108static void handle_output(unsigned long addr)
1109{
1110        struct device *i;
1111
1112        /* Check each device. */
1113        for (i = devices.dev; i; i = i->next) {
1114                struct virtqueue *vq;
1115
1116                /*
1117                 * Notifications to device descriptors mean they updated the
1118                 * device status.
1119                 */
1120                if (from_guest_phys(addr) == i->desc) {
1121                        update_device_status(i);
1122                        return;
1123                }
1124
1125                /* Devices should not be used before features are finalized. */
1126                for (vq = i->vq; vq; vq = vq->next) {
1127                        if (addr != vq->config.pfn*getpagesize())
1128                                continue;
1129                        errx(1, "Notification on %s before setup!", i->name);
1130                }
1131        }
1132
1133        /*
1134         * Early console write is done using notify on a nul-terminated string
1135         * in Guest memory.  It's also great for hacking debugging messages
1136         * into a Guest.
1137         */
1138        if (addr >= guest_limit)
1139                errx(1, "Bad NOTIFY %#lx", addr);
1140
1141        write(STDOUT_FILENO, from_guest_phys(addr),
1142              strnlen(from_guest_phys(addr), guest_limit - addr));
1143}
1144
1145/*L:190
1146 * Device Setup
1147 *
1148 * All devices need a descriptor so the Guest knows it exists, and a "struct
1149 * device" so the Launcher can keep track of it.  We have common helper
1150 * routines to allocate and manage them.
1151 */
1152
1153/*
1154 * The layout of the device page is a "struct lguest_device_desc" followed by a
1155 * number of virtqueue descriptors, then two sets of feature bits, then an
1156 * array of configuration bytes.  This routine returns the configuration
1157 * pointer.
1158 */
1159static u8 *device_config(const struct device *dev)
1160{
1161        return (void *)(dev->desc + 1)
1162                + dev->num_vq * sizeof(struct lguest_vqconfig)
1163                + dev->feature_len * 2;
1164}
1165
1166/*
1167 * This routine allocates a new "struct lguest_device_desc" from descriptor
1168 * table page just above the Guest's normal memory.  It returns a pointer to
1169 * that descriptor.
1170 */
1171static struct lguest_device_desc *new_dev_desc(u16 type)
1172{
1173        struct lguest_device_desc d = { .type = type };
1174        void *p;
1175
1176        /* Figure out where the next device config is, based on the last one. */
1177        if (devices.lastdev)
1178                p = device_config(devices.lastdev)
1179                        + devices.lastdev->desc->config_len;
1180        else
1181                p = devices.descpage;
1182
1183        /* We only have one page for all the descriptors. */
1184        if (p + sizeof(d) > (void *)devices.descpage + getpagesize())
1185                errx(1, "Too many devices");
1186
1187        /* p might not be aligned, so we memcpy in. */
1188        return memcpy(p, &d, sizeof(d));
1189}
1190
1191/*
1192 * Each device descriptor is followed by the description of its virtqueues.  We
1193 * specify how many descriptors the virtqueue is to have.
1194 */
1195static void add_virtqueue(struct device *dev, unsigned int num_descs,
1196                          void (*service)(struct virtqueue *))
1197{
1198        unsigned int pages;
1199        struct virtqueue **i, *vq = malloc(sizeof(*vq));
1200        void *p;
1201
1202        /* First we need some memory for this virtqueue. */
1203        pages = (vring_size(num_descs, LGUEST_VRING_ALIGN) + getpagesize() - 1)
1204                / getpagesize();
1205        p = get_pages(pages);
1206
1207        /* Initialize the virtqueue */
1208        vq->next = NULL;
1209        vq->last_avail_idx = 0;
1210        vq->dev = dev;
1211
1212        /*
1213         * This is the routine the service thread will run, and its Process ID
1214         * once it's running.
1215         */
1216        vq->service = service;
1217        vq->thread = (pid_t)-1;
1218
1219        /* Initialize the configuration. */
1220        vq->config.num = num_descs;
1221        vq->config.irq = devices.next_irq++;
1222        vq->config.pfn = to_guest_phys(p) / getpagesize();
1223
1224        /* Initialize the vring. */
1225        vring_init(&vq->vring, num_descs, p, LGUEST_VRING_ALIGN);
1226
1227        /*
1228         * Append virtqueue to this device's descriptor.  We use
1229         * device_config() to get the end of the device's current virtqueues;
1230         * we check that we haven't added any config or feature information
1231         * yet, otherwise we'd be overwriting them.
1232         */
1233        assert(dev->desc->config_len == 0 && dev->desc->feature_len == 0);
1234        memcpy(device_config(dev), &vq->config, sizeof(vq->config));
1235        dev->num_vq++;
1236        dev->desc->num_vq++;
1237
1238        verbose("Virtqueue page %#lx\n", to_guest_phys(p));
1239
1240        /*
1241         * Add to tail of list, so dev->vq is first vq, dev->vq->next is
1242         * second.
1243         */
1244        for (i = &dev->vq; *i; i = &(*i)->next);
1245        *i = vq;
1246}
1247
1248/*
1249 * The first half of the feature bitmask is for us to advertise features.  The
1250 * second half is for the Guest to accept features.
1251 */
1252static void add_feature(struct device *dev, unsigned bit)
1253{
1254        u8 *features = get_feature_bits(dev);
1255
1256        /* We can't extend the feature bits once we've added config bytes */
1257        if (dev->desc->feature_len <= bit / CHAR_BIT) {
1258                assert(dev->desc->config_len == 0);
1259                dev->feature_len = dev->desc->feature_len = (bit/CHAR_BIT) + 1;
1260        }
1261
1262        features[bit / CHAR_BIT] |= (1 << (bit % CHAR_BIT));
1263}
1264
1265/*
1266 * This routine sets the configuration fields for an existing device's
1267 * descriptor.  It only works for the last device, but that's OK because that's
1268 * how we use it.
1269 */
1270static void set_config(struct device *dev, unsigned len, const void *conf)
1271{
1272        /* Check we haven't overflowed our single page. */
1273        if (device_config(dev) + len > devices.descpage + getpagesize())
1274                errx(1, "Too many devices");
1275
1276        /* Copy in the config information, and store the length. */
1277        memcpy(device_config(dev), conf, len);
1278        dev->desc->config_len = len;
1279
1280        /* Size must fit in config_len field (8 bits)! */
1281        assert(dev->desc->config_len == len);
1282}
1283
1284/*
1285 * This routine does all the creation and setup of a new device, including
1286 * calling new_dev_desc() to allocate the descriptor and device memory.  We
1287 * don't actually start the service threads until later.
1288 *
1289 * See what I mean about userspace being boring?
1290 */
1291static struct device *new_device(const char *name, u16 type)
1292{
1293        struct device *dev = malloc(sizeof(*dev));
1294
1295        /* Now we populate the fields one at a time. */
1296        dev->desc = new_dev_desc(type);
1297        dev->name = name;
1298        dev->vq = NULL;
1299        dev->feature_len = 0;
1300        dev->num_vq = 0;
1301        dev->running = false;
1302
1303        /*
1304         * Append to device list.  Prepending to a single-linked list is
1305         * easier, but the user expects the devices to be arranged on the bus
1306         * in command-line order.  The first network device on the command line
1307         * is eth0, the first block device /dev/vda, etc.
1308         */
1309        if (devices.lastdev)
1310                devices.lastdev->next = dev;
1311        else
1312                devices.dev = dev;
1313        devices.lastdev = dev;
1314
1315        return dev;
1316}
1317
1318/*
1319 * Our first setup routine is the console.  It's a fairly simple device, but
1320 * UNIX tty handling makes it uglier than it could be.
1321 */
1322static void setup_console(void)
1323{
1324        struct device *dev;
1325
1326        /* If we can save the initial standard input settings... */
1327        if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
1328                struct termios term = orig_term;
1329                /*
1330                 * Then we turn off echo, line buffering and ^C etc: We want a
1331                 * raw input stream to the Guest.
1332                 */
1333                term.c_lflag &= ~(ISIG|ICANON|ECHO);
1334                tcsetattr(STDIN_FILENO, TCSANOW, &term);
1335        }
1336
1337        dev = new_device("console", VIRTIO_ID_CONSOLE);
1338
1339        /* We store the console state in dev->priv, and initialize it. */
1340        dev->priv = malloc(sizeof(struct console_abort));
1341        ((struct console_abort *)dev->priv)->count = 0;
1342
1343        /*
1344         * The console needs two virtqueues: the input then the output.  When
1345         * they put something the input queue, we make sure we're listening to
1346         * stdin.  When they put something in the output queue, we write it to
1347         * stdout.
1348         */
1349        add_virtqueue(dev, VIRTQUEUE_NUM, console_input);
1350        add_virtqueue(dev, VIRTQUEUE_NUM, console_output);
1351
1352        verbose("device %u: console\n", ++devices.device_num);
1353}
1354/*:*/
1355
1356/*M:010
1357 * Inter-guest networking is an interesting area.  Simplest is to have a
1358 * --sharenet=<name> option which opens or creates a named pipe.  This can be
1359 * used to send packets to another guest in a 1:1 manner.
1360 *
1361 * More sophisticated is to use one of the tools developed for project like UML
1362 * to do networking.
1363 *
1364 * Faster is to do virtio bonding in kernel.  Doing this 1:1 would be
1365 * completely generic ("here's my vring, attach to your vring") and would work
1366 * for any traffic.  Of course, namespace and permissions issues need to be
1367 * dealt with.  A more sophisticated "multi-channel" virtio_net.c could hide
1368 * multiple inter-guest channels behind one interface, although it would
1369 * require some manner of hotplugging new virtio channels.
1370 *
1371 * Finally, we could use a virtio network switch in the kernel, ie. vhost.
1372:*/
1373
1374static u32 str2ip(const char *ipaddr)
1375{
1376        unsigned int b[4];
1377
1378        if (sscanf(ipaddr, "%u.%u.%u.%u", &b[0], &b[1], &b[2], &b[3]) != 4)
1379                errx(1, "Failed to parse IP address '%s'", ipaddr);
1380        return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | b[3];
1381}
1382
1383static void str2mac(const char *macaddr, unsigned char mac[6])
1384{
1385        unsigned int m[6];
1386        if (sscanf(macaddr, "%02x:%02x:%02x:%02x:%02x:%02x",
1387                   &m[0], &m[1], &m[2], &m[3], &m[4], &m[5]) != 6)
1388                errx(1, "Failed to parse mac address '%s'", macaddr);
1389        mac[0] = m[0];
1390        mac[1] = m[1];
1391        mac[2] = m[2];
1392        mac[3] = m[3];
1393        mac[4] = m[4];
1394        mac[5] = m[5];
1395}
1396
1397/*
1398 * This code is "adapted" from libbridge: it attaches the Host end of the
1399 * network device to the bridge device specified by the command line.
1400 *
1401 * This is yet another James Morris contribution (I'm an IP-level guy, so I
1402 * dislike bridging), and I just try not to break it.
1403 */
1404static void add_to_bridge(int fd, const char *if_name, const char *br_name)
1405{
1406        int ifidx;
1407        struct ifreq ifr;
1408
1409        if (!*br_name)
1410                errx(1, "must specify bridge name");
1411
1412        ifidx = if_nametoindex(if_name);
1413        if (!ifidx)
1414                errx(1, "interface %s does not exist!", if_name);
1415
1416        strncpy(ifr.ifr_name, br_name, IFNAMSIZ);
1417        ifr.ifr_name[IFNAMSIZ-1] = '\0';
1418        ifr.ifr_ifindex = ifidx;
1419        if (ioctl(fd, SIOCBRADDIF, &ifr) < 0)
1420                err(1, "can't add %s to bridge %s", if_name, br_name);
1421}
1422
1423/*
1424 * This sets up the Host end of the network device with an IP address, brings
1425 * it up so packets will flow, the copies the MAC address into the hwaddr
1426 * pointer.
1427 */
1428static void configure_device(int fd, const char *tapif, u32 ipaddr)
1429{
1430        struct ifreq ifr;
1431        struct sockaddr_in sin;
1432
1433        memset(&ifr, 0, sizeof(ifr));
1434        strcpy(ifr.ifr_name, tapif);
1435
1436        /* Don't read these incantations.  Just cut & paste them like I did! */
1437        sin.sin_family = AF_INET;
1438        sin.sin_addr.s_addr = htonl(ipaddr);
1439        memcpy(&ifr.ifr_addr, &sin, sizeof(sin));
1440        if (ioctl(fd, SIOCSIFADDR, &ifr) != 0)
1441                err(1, "Setting %s interface address", tapif);
1442        ifr.ifr_flags = IFF_UP;
1443        if (ioctl(fd, SIOCSIFFLAGS, &ifr) != 0)
1444                err(1, "Bringing interface %s up", tapif);
1445}
1446
1447static int get_tun_device(char tapif[IFNAMSIZ])
1448{
1449        struct ifreq ifr;
1450        int netfd;
1451
1452        /* Start with this zeroed.  Messy but sure. */
1453        memset(&ifr, 0, sizeof(ifr));
1454
1455        /*
1456         * We open the /dev/net/tun device and tell it we want a tap device.  A
1457         * tap device is like a tun device, only somehow different.  To tell
1458         * the truth, I completely blundered my way through this code, but it
1459         * works now!
1460         */
1461        netfd = open_or_die("/dev/net/tun", O_RDWR);
1462        ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
1463        strcpy(ifr.ifr_name, "tap%d");
1464        if (ioctl(netfd, TUNSETIFF, &ifr) != 0)
1465                err(1, "configuring /dev/net/tun");
1466
1467        if (ioctl(netfd, TUNSETOFFLOAD,
1468                  TUN_F_CSUM|TUN_F_TSO4|TUN_F_TSO6|TUN_F_TSO_ECN) != 0)
1469                err(1, "Could not set features for tun device");
1470
1471        /*
1472         * We don't need checksums calculated for packets coming in this
1473         * device: trust us!
1474         */
1475        ioctl(netfd, TUNSETNOCSUM, 1);
1476
1477        memcpy(tapif, ifr.ifr_name, IFNAMSIZ);
1478        return netfd;
1479}
1480
1481/*L:195
1482 * Our network is a Host<->Guest network.  This can either use bridging or
1483 * routing, but the principle is the same: it uses the "tun" device to inject
1484 * packets into the Host as if they came in from a normal network card.  We
1485 * just shunt packets between the Guest and the tun device.
1486 */
1487static void setup_tun_net(char *arg)
1488{
1489        struct device *dev;
1490        struct net_info *net_info = malloc(sizeof(*net_info));
1491        int ipfd;
1492        u32 ip = INADDR_ANY;
1493        bool bridging = false;
1494        char tapif[IFNAMSIZ], *p;
1495        struct virtio_net_config conf;
1496
1497        net_info->tunfd = get_tun_device(tapif);
1498
1499        /* First we create a new network device. */
1500        dev = new_device("net", VIRTIO_ID_NET);
1501        dev->priv = net_info;
1502
1503        /* Network devices need a recv and a send queue, just like console. */
1504        add_virtqueue(dev, VIRTQUEUE_NUM, net_input);
1505        add_virtqueue(dev, VIRTQUEUE_NUM, net_output);
1506
1507        /*
1508         * We need a socket to perform the magic network ioctls to bring up the
1509         * tap interface, connect to the bridge etc.  Any socket will do!
1510         */
1511        ipfd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
1512        if (ipfd < 0)
1513                err(1, "opening IP socket");
1514
1515        /* If the command line was --tunnet=bridge:<name> do bridging. */
1516        if (!strncmp(BRIDGE_PFX, arg, strlen(BRIDGE_PFX))) {
1517                arg += strlen(BRIDGE_PFX);
1518                bridging = true;
1519        }
1520
1521        /* A mac address may follow the bridge name or IP address */
1522        p = strchr(arg, ':');
1523        if (p) {
1524                str2mac(p+1, conf.mac);
1525                add_feature(dev, VIRTIO_NET_F_MAC);
1526                *p = '\0';
1527        }
1528
1529        /* arg is now either an IP address or a bridge name */
1530        if (bridging)
1531                add_to_bridge(ipfd, tapif, arg);
1532        else
1533                ip = str2ip(arg);
1534
1535        /* Set up the tun device. */
1536        configure_device(ipfd, tapif, ip);
1537
1538        /* Expect Guest to handle everything except UFO */
1539        add_feature(dev, VIRTIO_NET_F_CSUM);
1540        add_feature(dev, VIRTIO_NET_F_GUEST_CSUM);
1541        add_feature(dev, VIRTIO_NET_F_GUEST_TSO4);
1542        add_feature(dev, VIRTIO_NET_F_GUEST_TSO6);
1543        add_feature(dev, VIRTIO_NET_F_GUEST_ECN);
1544        add_feature(dev, VIRTIO_NET_F_HOST_TSO4);
1545        add_feature(dev, VIRTIO_NET_F_HOST_TSO6);
1546        add_feature(dev, VIRTIO_NET_F_HOST_ECN);
1547        /* We handle indirect ring entries */
1548        add_feature(dev, VIRTIO_RING_F_INDIRECT_DESC);
1549        set_config(dev, sizeof(conf), &conf);
1550
1551        /* We don't need the socket any more; setup is done. */
1552        close(ipfd);
1553
1554        devices.device_num++;
1555
1556        if (bridging)
1557                verbose("device %u: tun %s attached to bridge: %s\n",
1558                        devices.device_num, tapif, arg);
1559        else
1560                verbose("device %u: tun %s: %s\n",
1561                        devices.device_num, tapif, arg);
1562}
1563/*:*/
1564
1565/* This hangs off device->priv. */
1566struct vblk_info {
1567        /* The size of the file. */
1568        off64_t len;
1569
1570        /* The file descriptor for the file. */
1571        int fd;
1572
1573};
1574
1575/*L:210
1576 * The Disk
1577 *
1578 * The disk only has one virtqueue, so it only has one thread.  It is really
1579 * simple: the Guest asks for a block number and we read or write that position
1580 * in the file.
1581 *
1582 * Before we serviced each virtqueue in a separate thread, that was unacceptably
1583 * slow: the Guest waits until the read is finished before running anything
1584 * else, even if it could have been doing useful work.
1585 *
1586 * We could have used async I/O, except it's reputed to suck so hard that
1587 * characters actually go missing from your code when you try to use it.
1588 */
1589static void blk_request(struct virtqueue *vq)
1590{
1591        struct vblk_info *vblk = vq->dev->priv;
1592        unsigned int head, out_num, in_num, wlen;
1593        int ret;
1594        u8 *in;
1595        struct virtio_blk_outhdr *out;
1596        struct iovec iov[vq->vring.num];
1597        off64_t off;
1598
1599        /*
1600         * Get the next request, where we normally wait.  It triggers the
1601         * interrupt to acknowledge previously serviced requests (if any).
1602         */
1603        head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
1604
1605        /*
1606         * Every block request should contain at least one output buffer
1607         * (detailing the location on disk and the type of request) and one
1608         * input buffer (to hold the result).
1609         */
1610        if (out_num == 0 || in_num == 0)
1611                errx(1, "Bad virtblk cmd %u out=%u in=%u",
1612                     head, out_num, in_num);
1613
1614        out = convert(&iov[0], struct virtio_blk_outhdr);
1615        in = convert(&iov[out_num+in_num-1], u8);
1616        /*
1617         * For historical reasons, block operations are expressed in 512 byte
1618         * "sectors".
1619         */
1620        off = out->sector * 512;
1621
1622        /*
1623         * In general the virtio block driver is allowed to try SCSI commands.
1624         * It'd be nice if we supported eject, for example, but we don't.
1625         */
1626        if (out->type & VIRTIO_BLK_T_SCSI_CMD) {
1627                fprintf(stderr, "Scsi commands unsupported\n");
1628                *in = VIRTIO_BLK_S_UNSUPP;
1629                wlen = sizeof(*in);
1630        } else if (out->type & VIRTIO_BLK_T_OUT) {
1631                /*
1632                 * Write
1633                 *
1634                 * Move to the right location in the block file.  This can fail
1635                 * if they try to write past end.
1636                 */
1637                if (lseek64(vblk->fd, off, SEEK_SET) != off)
1638                        err(1, "Bad seek to sector %llu", out->sector);
1639
1640                ret = writev(vblk->fd, iov+1, out_num-1);
1641                verbose("WRITE to sector %llu: %i\n", out->sector, ret);
1642
1643                /*
1644                 * Grr... Now we know how long the descriptor they sent was, we
1645                 * make sure they didn't try to write over the end of the block
1646                 * file (possibly extending it).
1647                 */
1648                if (ret > 0 && off + ret > vblk->len) {
1649                        /* Trim it back to the correct length */
1650                        ftruncate64(vblk->fd, vblk->len);
1651                        /* Die, bad Guest, die. */
1652                        errx(1, "Write past end %llu+%u", off, ret);
1653                }
1654
1655                wlen = sizeof(*in);
1656                *in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
1657        } else if (out->type & VIRTIO_BLK_T_FLUSH) {
1658                /* Flush */
1659                ret = fdatasync(vblk->fd);
1660                verbose("FLUSH fdatasync: %i\n", ret);
1661                wlen = sizeof(*in);
1662                *in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
1663        } else {
1664                /*
1665                 * Read
1666                 *
1667                 * Move to the right location in the block file.  This can fail
1668                 * if they try to read past end.
1669                 */
1670                if (lseek64(vblk->fd, off, SEEK_SET) != off)
1671                        err(1, "Bad seek to sector %llu", out->sector);
1672
1673                ret = readv(vblk->fd, iov+1, in_num-1);
1674                verbose("READ from sector %llu: %i\n", out->sector, ret);
1675                if (ret >= 0) {
1676                        wlen = sizeof(*in) + ret;
1677                        *in = VIRTIO_BLK_S_OK;
1678                } else {
1679                        wlen = sizeof(*in);
1680                        *in = VIRTIO_BLK_S_IOERR;
1681                }
1682        }
1683
1684        /* Finished that request. */
1685        add_used(vq, head, wlen);
1686}
1687
1688/*L:198 This actually sets up a virtual block device. */
1689static void setup_block_file(const char *filename)
1690{
1691        struct device *dev;
1692        struct vblk_info *vblk;
1693        struct virtio_blk_config conf;
1694
1695        /* Creat the device. */
1696        dev = new_device("block", VIRTIO_ID_BLOCK);
1697
1698        /* The device has one virtqueue, where the Guest places requests. */
1699        add_virtqueue(dev, VIRTQUEUE_NUM, blk_request);
1700
1701        /* Allocate the room for our own bookkeeping */
1702        vblk = dev->priv = malloc(sizeof(*vblk));
1703
1704        /* First we open the file and store the length. */
1705        vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
1706        vblk->len = lseek64(vblk->fd, 0, SEEK_END);
1707
1708        /* We support FLUSH. */
1709        add_feature(dev, VIRTIO_BLK_F_FLUSH);
1710
1711        /* Tell Guest how many sectors this device has. */
1712        conf.capacity = cpu_to_le64(vblk->len / 512);
1713
1714        /*
1715         * Tell Guest not to put in too many descriptors at once: two are used
1716         * for the in and out elements.
1717         */
1718        add_feature(dev, VIRTIO_BLK_F_SEG_MAX);
1719        conf.seg_max = cpu_to_le32(VIRTQUEUE_NUM - 2);
1720
1721        /* Don't try to put whole struct: we have 8 bit limit. */
1722        set_config(dev, offsetof(struct virtio_blk_config, geometry), &conf);
1723
1724        verbose("device %u: virtblock %llu sectors\n",
1725                ++devices.device_num, le64_to_cpu(conf.capacity));
1726}
1727
1728/*L:211
1729 * Our random number generator device reads from /dev/random into the Guest's
1730 * input buffers.  The usual case is that the Guest doesn't want random numbers
1731 * and so has no buffers although /dev/random is still readable, whereas
1732 * console is the reverse.
1733 *
1734 * The same logic applies, however.
1735 */
1736struct rng_info {
1737        int rfd;
1738};
1739
1740static void rng_input(struct virtqueue *vq)
1741{
1742        int len;
1743        unsigned int head, in_num, out_num, totlen = 0;
1744        struct rng_info *rng_info = vq->dev->priv;
1745        struct iovec iov[vq->vring.num];
1746
1747        /* First we need a buffer from the Guests's virtqueue. */
1748        head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
1749        if (out_num)
1750                errx(1, "Output buffers in rng?");
1751
1752        /*
1753         * Just like the console write, we loop to cover the whole iovec.
1754         * In this case, short reads actually happen quite a bit.
1755         */
1756        while (!iov_empty(iov, in_num)) {
1757                len = readv(rng_info->rfd, iov, in_num);
1758                if (len <= 0)
1759                        err(1, "Read from /dev/random gave %i", len);
1760                iov_consume(iov, in_num, len);
1761                totlen += len;
1762        }
1763
1764        /* Tell the Guest about the new input. */
1765        add_used(vq, head, totlen);
1766}
1767
1768/*L:199
1769 * This creates a "hardware" random number device for the Guest.
1770 */
1771static void setup_rng(void)
1772{
1773        struct device *dev;
1774        struct rng_info *rng_info = malloc(sizeof(*rng_info));
1775
1776        /* Our device's privat info simply contains the /dev/random fd. */
1777        rng_info->rfd = open_or_die("/dev/random", O_RDONLY);
1778
1779        /* Create the new device. */
1780        dev = new_device("rng", VIRTIO_ID_RNG);
1781        dev->priv = rng_info;
1782
1783        /* The device has one virtqueue, where the Guest places inbufs. */
1784        add_virtqueue(dev, VIRTQUEUE_NUM, rng_input);
1785
1786        verbose("device %u: rng\n", devices.device_num++);
1787}
1788/* That's the end of device setup. */
1789
1790/*L:230 Reboot is pretty easy: clean up and exec() the Launcher afresh. */
1791static void __attribute__((noreturn)) restart_guest(void)
1792{
1793        unsigned int i;
1794
1795        /*
1796         * Since we don't track all open fds, we simply close everything beyond
1797         * stderr.
1798         */
1799        for (i = 3; i < FD_SETSIZE; i++)
1800                close(i);
1801
1802        /* Reset all the devices (kills all threads). */
1803        cleanup_devices();
1804
1805        execv(main_args[0], main_args);
1806        err(1, "Could not exec %s", main_args[0]);
1807}
1808
1809/*L:220
1810 * Finally we reach the core of the Launcher which runs the Guest, serves
1811 * its input and output, and finally, lays it to rest.
1812 */
1813static void __attribute__((noreturn)) run_guest(void)
1814{
1815        for (;;) {
1816                unsigned long notify_addr;
1817                int readval;
1818
1819                /* We read from the /dev/lguest device to run the Guest. */
1820                readval = pread(lguest_fd, &notify_addr,
1821                                sizeof(notify_addr), cpu_id);
1822
1823                /* One unsigned long means the Guest did HCALL_NOTIFY */
1824                if (readval == sizeof(notify_addr)) {
1825                        verbose("Notify on address %#lx\n", notify_addr);
1826                        handle_output(notify_addr);
1827                /* ENOENT means the Guest died.  Reading tells us why. */
1828                } else if (errno == ENOENT) {
1829                        char reason[1024] = { 0 };
1830                        pread(lguest_fd, reason, sizeof(reason)-1, cpu_id);
1831                        errx(1, "%s", reason);
1832                /* ERESTART means that we need to reboot the guest */
1833                } else if (errno == ERESTART) {
1834                        restart_guest();
1835                /* Anything else means a bug or incompatible change. */
1836                } else
1837                        err(1, "Running guest failed");
1838        }
1839}
1840/*L:240
1841 * This is the end of the Launcher.  The good news: we are over halfway
1842 * through!  The bad news: the most fiendish part of the code still lies ahead
1843 * of us.
1844 *
1845 * Are you ready?  Take a deep breath and join me in the core of the Host, in
1846 * "make Host".
1847:*/
1848
1849static struct option opts[] = {
1850        { "verbose", 0, NULL, 'v' },
1851        { "tunnet", 1, NULL, 't' },
1852        { "block", 1, NULL, 'b' },
1853        { "rng", 0, NULL, 'r' },
1854        { "initrd", 1, NULL, 'i' },
1855        { "username", 1, NULL, 'u' },
1856        { "chroot", 1, NULL, 'c' },
1857        { NULL },
1858};
1859static void usage(void)
1860{
1861        errx(1, "Usage: lguest [--verbose] "
1862             "[--tunnet=(<ipaddr>:<macaddr>|bridge:<bridgename>:<macaddr>)\n"
1863             "|--block=<filename>|--initrd=<filename>]...\n"
1864             "<mem-in-mb> vmlinux [args...]");
1865}
1866
1867/*L:105 The main routine is where the real work begins: */
1868int main(int argc, char *argv[])
1869{
1870        /* Memory, code startpoint and size of the (optional) initrd. */
1871        unsigned long mem = 0, start, initrd_size = 0;
1872        /* Two temporaries. */
1873        int i, c;
1874        /* The boot information for the Guest. */
1875        struct boot_params *boot;
1876        /* If they specify an initrd file to load. */
1877        const char *initrd_name = NULL;
1878
1879        /* Password structure for initgroups/setres[gu]id */
1880        struct passwd *user_details = NULL;
1881
1882        /* Directory to chroot to */
1883        char *chroot_path = NULL;
1884
1885        /* Save the args: we "reboot" by execing ourselves again. */
1886        main_args = argv;
1887
1888        /*
1889         * First we initialize the device list.  We keep a pointer to the last
1890         * device, and the next interrupt number to use for devices (1:
1891         * remember that 0 is used by the timer).
1892         */
1893        devices.lastdev = NULL;
1894        devices.next_irq = 1;
1895
1896        /* We're CPU 0.  In fact, that's the only CPU possible right now. */
1897        cpu_id = 0;
1898
1899        /*
1900         * We need to know how much memory so we can set up the device
1901         * descriptor and memory pages for the devices as we parse the command
1902         * line.  So we quickly look through the arguments to find the amount
1903         * of memory now.
1904         */
1905        for (i = 1; i < argc; i++) {
1906                if (argv[i][0] != '-') {
1907                        mem = atoi(argv[i]) * 1024 * 1024;
1908                        /*
1909                         * We start by mapping anonymous pages over all of
1910                         * guest-physical memory range.  This fills it with 0,
1911                         * and ensures that the Guest won't be killed when it
1912                         * tries to access it.
1913                         */
1914                        guest_base = map_zeroed_pages(mem / getpagesize()
1915                                                      + DEVICE_PAGES);
1916                        guest_limit = mem;
1917                        guest_max = mem + DEVICE_PAGES*getpagesize();
1918                        devices.descpage = get_pages(1);
1919                        break;
1920                }
1921        }
1922
1923        /* The options are fairly straight-forward */
1924        while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
1925                switch (c) {
1926                case 'v':
1927                        verbose = true;
1928                        break;
1929                case 't':
1930                        setup_tun_net(optarg);
1931                        break;
1932                case 'b':
1933                        setup_block_file(optarg);
1934                        break;
1935                case 'r':
1936                        setup_rng();
1937                        break;
1938                case 'i':
1939                        initrd_name = optarg;
1940                        break;
1941                case 'u':
1942                        user_details = getpwnam(optarg);
1943                        if (!user_details)
1944                                err(1, "getpwnam failed, incorrect username?");
1945                        break;
1946                case 'c':
1947                        chroot_path = optarg;
1948                        break;
1949                default:
1950                        warnx("Unknown argument %s", argv[optind]);
1951                        usage();
1952                }
1953        }
1954        /*
1955         * After the other arguments we expect memory and kernel image name,
1956         * followed by command line arguments for the kernel.
1957         */
1958        if (optind + 2 > argc)
1959                usage();
1960
1961        verbose("Guest base is at %p\n", guest_base);
1962
1963        /* We always have a console device */
1964        setup_console();
1965
1966        /* Now we load the kernel */
1967        start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));
1968
1969        /* Boot information is stashed at physical address 0 */
1970        boot = from_guest_phys(0);
1971
1972        /* Map the initrd image if requested (at top of physical memory) */
1973        if (initrd_name) {
1974                initrd_size = load_initrd(initrd_name, mem);
1975                /*
1976                 * These are the location in the Linux boot header where the
1977                 * start and size of the initrd are expected to be found.
1978                 */
1979                boot->hdr.ramdisk_image = mem - initrd_size;
1980                boot->hdr.ramdisk_size = initrd_size;
1981                /* The bootloader type 0xFF means "unknown"; that's OK. */
1982                boot->hdr.type_of_loader = 0xFF;
1983        }
1984
1985        /*
1986         * The Linux boot header contains an "E820" memory map: ours is a
1987         * simple, single region.
1988         */
1989        boot->e820_entries = 1;
1990        boot->e820_map[0] = ((struct e820entry) { 0, mem, E820_RAM });
1991        /*
1992         * The boot header contains a command line pointer: we put the command
1993         * line after the boot header.
1994         */
1995        boot->hdr.cmd_line_ptr = to_guest_phys(boot + 1);
1996        /* We use a simple helper to copy the arguments separated by spaces. */
1997        concat((char *)(boot + 1), argv+optind+2);
1998
1999        /* Set kernel alignment to 16M (CONFIG_PHYSICAL_ALIGN) */
2000        boot->hdr.kernel_alignment = 0x1000000;
2001
2002        /* Boot protocol version: 2.07 supports the fields for lguest. */
2003        boot->hdr.version = 0x207;
2004
2005        /* The hardware_subarch value of "1" tells the Guest it's an lguest. */
2006        boot->hdr.hardware_subarch = 1;
2007
2008        /* Tell the entry path not to try to reload segment registers. */
2009        boot->hdr.loadflags |= KEEP_SEGMENTS;
2010
2011        /* We tell the kernel to initialize the Guest. */
2012        tell_kernel(start);
2013
2014        /* Ensure that we terminate if a device-servicing child dies. */
2015        signal(SIGCHLD, kill_launcher);
2016
2017        /* If we exit via err(), this kills all the threads, restores tty. */
2018        atexit(cleanup_devices);
2019
2020        /* If requested, chroot to a directory */
2021        if (chroot_path) {
2022                if (chroot(chroot_path) != 0)
2023                        err(1, "chroot(\"%s\") failed", chroot_path);
2024
2025                if (chdir("/") != 0)
2026                        err(1, "chdir(\"/\") failed");
2027
2028                verbose("chroot done\n");
2029        }
2030
2031        /* If requested, drop privileges */
2032        if (user_details) {
2033                uid_t u;
2034                gid_t g;
2035
2036                u = user_details->pw_uid;
2037                g = user_details->pw_gid;
2038
2039                if (initgroups(user_details->pw_name, g) != 0)
2040                        err(1, "initgroups failed");
2041
2042                if (setresgid(g, g, g) != 0)
2043                        err(1, "setresgid failed");
2044
2045                if (setresuid(u, u, u) != 0)
2046                        err(1, "setresuid failed");
2047
2048                verbose("Dropping privileges completed\n");
2049        }
2050
2051        /* Finally, run the Guest.  This doesn't return. */
2052        run_guest();
2053}
2054/*:*/
2055
2056/*M:999
2057 * Mastery is done: you now know everything I do.
2058 *
2059 * But surely you have seen code, features and bugs in your wanderings which
2060 * you now yearn to attack?  That is the real game, and I look forward to you
2061 * patching and forking lguest into the Your-Name-Here-visor.
2062 *
2063 * Farewell, and good coding!
2064 * Rusty Russell.
2065 */
2066
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