blob: 32cf2ce15d69bcfca9c24da9ad318fc1a2e84eb2 [file] [log] [blame]
* 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 opens /dev/lguest to tell the kernel about the Guest and
* control it.
#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <err.h>
#include <stdint.h>
#include <stdlib.h>
#include <elf.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/eventfd.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 <assert.h>
#include <sched.h>
#include <limits.h>
#include <stddef.h>
#include <signal.h>
#include <pwd.h>
#include <grp.h>
* We can ignore the 43 include files we need for this program, but I do want
* to draw attention to the use of kernel-style types.
* As Linus said, "C is a Spartan language, and so should your naming be." I
* like these abbreviations, so we define them here. Note that u64 is always
* unsigned long long, which works on all Linux systems: this means that we can
* use %llu in printf for any u64.
typedef unsigned long long u64;
typedef uint32_t u32;
typedef uint16_t u16;
typedef uint8_t u8;
#include <linux/virtio_config.h>
#include <linux/virtio_net.h>
#include <linux/virtio_blk.h>
#include <linux/virtio_console.h>
#include <linux/virtio_rng.h>
#include <linux/virtio_ring.h>
#include <asm/bootparam.h>
#include "../../include/linux/lguest_launcher.h"
#define BRIDGE_PFX "bridge:"
#define SIOCBRADDIF 0x89a2 /* add interface to bridge */
/* We can have up to 256 pages for devices. */
#define DEVICE_PAGES 256
/* This will occupy 3 pages: it must be a power of 2. */
#define VIRTQUEUE_NUM 256
* verbose is both a global flag and a macro. The C preprocessor allows
* this, and although I wouldn't recommend it, it works quite nicely here.
static bool verbose;
#define verbose(args...) \
do { if (verbose) printf(args); } while(0)
/* The pointer to the start of guest memory. */
static void *guest_base;
/* The maximum guest physical address allowed, and maximum possible. */
static unsigned long guest_limit, guest_max;
/* The /dev/lguest file descriptor. */
static int lguest_fd;
/* a per-cpu variable indicating whose vcpu is currently running */
static unsigned int __thread cpu_id;
/* This is our list of devices. */
struct device_list {
/* Counter to assign interrupt numbers. */
unsigned int next_irq;
/* Counter to print out convenient device numbers. */
unsigned int device_num;
/* The descriptor page for the devices. */
u8 *descpage;
/* A single linked list of devices. */
struct device *dev;
/* And a pointer to the last device for easy append. */
struct device *lastdev;
/* The list of Guest devices, based on command line arguments. */
static struct device_list devices;
/* The device structure describes a single device. */
struct device {
/* The linked-list pointer. */
struct device *next;
/* The device's descriptor, as mapped into the Guest. */
struct lguest_device_desc *desc;
/* We can't trust desc values once Guest has booted: we use these. */
unsigned int feature_len;
unsigned int num_vq;
/* The name of this device, for --verbose. */
const char *name;
/* Any queues attached to this device */
struct virtqueue *vq;
/* Is it operational */
bool running;
/* Device-specific data. */
void *priv;
/* The virtqueue structure describes a queue attached to a device. */
struct virtqueue {
struct virtqueue *next;
/* Which device owns me. */
struct device *dev;
/* The configuration for this queue. */
struct lguest_vqconfig config;
/* The actual ring of buffers. */
struct vring vring;
/* Last available index we saw. */
u16 last_avail_idx;
/* How many are used since we sent last irq? */
unsigned int pending_used;
/* Eventfd where Guest notifications arrive. */
int eventfd;
/* Function for the thread which is servicing this virtqueue. */
void (*service)(struct virtqueue *vq);
pid_t thread;
/* Remember the arguments to the program so we can "reboot" */
static char **main_args;
/* The original tty settings to restore on exit. */
static struct termios orig_term;
* We have to be careful with barriers: our devices are all run in separate
* threads and so we need to make sure that changes visible to the Guest happen
* in precise order.
#define wmb() __asm__ __volatile__("" : : : "memory")
#define rmb() __asm__ __volatile__("lock; addl $0,0(%%esp)" : : : "memory")
#define mb() __asm__ __volatile__("lock; addl $0,0(%%esp)" : : : "memory")
/* Wrapper for the last available index. Makes it easier to change. */
#define lg_last_avail(vq) ((vq)->last_avail_idx)
* The virtio configuration space is defined to be little-endian. x86 is
* little-endian too, but it's nice to be explicit so we have these helpers.
#define cpu_to_le16(v16) (v16)
#define cpu_to_le32(v32) (v32)
#define cpu_to_le64(v64) (v64)
#define le16_to_cpu(v16) (v16)
#define le32_to_cpu(v32) (v32)
#define le64_to_cpu(v64) (v64)
/* Is this iovec empty? */
static bool iov_empty(const struct iovec iov[], unsigned int num_iov)
unsigned int i;
for (i = 0; i < num_iov; i++)
if (iov[i].iov_len)
return false;
return true;
/* Take len bytes from the front of this iovec. */
static void iov_consume(struct iovec iov[], unsigned num_iov,
void *dest, unsigned len)
unsigned int i;
for (i = 0; i < num_iov; i++) {
unsigned int used;
used = iov[i].iov_len < len ? iov[i].iov_len : len;
if (dest) {
memcpy(dest, iov[i].iov_base, used);
dest += used;
iov[i].iov_base += used;
iov[i].iov_len -= used;
len -= used;
if (len != 0)
errx(1, "iovec too short!");
/* The device virtqueue descriptors are followed by feature bitmasks. */
static u8 *get_feature_bits(struct device *dev)
return (u8 *)(dev->desc + 1)
+ dev->num_vq * sizeof(struct lguest_vqconfig);
* The Launcher code itself takes us out into userspace, that scary place where
* pointers run wild and free! Unfortunately, like most userspace programs,
* it's quite boring (which is why everyone likes to hack on the kernel!).
* Perhaps if you make up an Lguest Drinking Game at this point, it will get
* you through this section. Or, maybe not.
* The Launcher sets up a big chunk of memory to be the Guest's "physical"
* memory and stores it in "guest_base". In other words, Guest physical ==
* Launcher virtual with an offset.
* This can be tough to get your head around, but usually it just means that we
* use these trivial conversion functions when the Guest gives us its
* "physical" addresses:
static void *from_guest_phys(unsigned long addr)
return guest_base + addr;
static unsigned long to_guest_phys(const void *addr)
return (addr - guest_base);
* Loading the Kernel.
* We start with couple of simple helper routines. open_or_die() avoids
* error-checking code cluttering the callers:
static int open_or_die(const char *name, int flags)
int fd = open(name, flags);
if (fd < 0)
err(1, "Failed to open %s", name);
return fd;
/* map_zeroed_pages() takes a number of pages. */
static void *map_zeroed_pages(unsigned int num)
int fd = open_or_die("/dev/zero", O_RDONLY);
void *addr;
* We use a private mapping (ie. if we write to the page, it will be
* copied). We allocate an extra two pages PROT_NONE to act as guard
* pages against read/write attempts that exceed allocated space.
addr = mmap(NULL, getpagesize() * (num+2),
if (addr == MAP_FAILED)
err(1, "Mmapping %u pages of /dev/zero", num);
if (mprotect(addr + getpagesize(), getpagesize() * num,
err(1, "mprotect rw %u pages failed", num);
* One neat mmap feature is that you can close the fd, and it
* stays mapped.
/* Return address after PROT_NONE page */
return addr + getpagesize();
/* Get some more pages for a device. */
static void *get_pages(unsigned int num)
void *addr = from_guest_phys(guest_limit);
guest_limit += num * getpagesize();
if (guest_limit > guest_max)
errx(1, "Not enough memory for devices");
return addr;
* This routine is used to load the kernel or initrd. It tries mmap, but if
* that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
* it falls back to reading the memory in.
static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
ssize_t r;
* We map writable even though for some segments are marked read-only.
* The kernel really wants to be writable: it patches its own
* instructions.
* MAP_PRIVATE means that the page won't be copied until a write is
* done to it. This allows us to share untouched memory between
* Guests.
if (mmap(addr, len, PROT_READ|PROT_WRITE,
/* pread does a seek and a read in one shot: saves a few lines. */
r = pread(fd, addr, len, offset);
if (r != len)
err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
* This routine takes an open vmlinux image, which is in ELF, and maps it into
* the Guest memory. ELF = Embedded Linking Format, which is the format used
* by all modern binaries on Linux including the kernel.
* The ELF headers give *two* addresses: a physical address, and a virtual
* address. We use the physical address; the Guest will map itself to the
* virtual address.
* We return the starting address.
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr)
Elf32_Phdr phdr[ehdr->e_phnum];
unsigned int i;
* Sanity checks on the main ELF header: an x86 executable with a
* reasonable number of correctly-sized program headers.
if (ehdr->e_type != ET_EXEC
|| ehdr->e_machine != EM_386
|| ehdr->e_phentsize != sizeof(Elf32_Phdr)
|| ehdr->e_phnum < 1 || ehdr->e_phnum > 65536U/sizeof(Elf32_Phdr))
errx(1, "Malformed elf header");
* An ELF executable contains an ELF header and a number of "program"
* headers which indicate which parts ("segments") of the program to
* load where.
/* We read in all the program headers at once: */
if (lseek(elf_fd, ehdr->e_phoff, SEEK_SET) < 0)
err(1, "Seeking to program headers");
if (read(elf_fd, phdr, sizeof(phdr)) != sizeof(phdr))
err(1, "Reading program headers");
* Try all the headers: there are usually only three. A read-only one,
* a read-write one, and a "note" section which we don't load.
for (i = 0; i < ehdr->e_phnum; i++) {
/* If this isn't a loadable segment, we ignore it */
if (phdr[i].p_type != PT_LOAD)
verbose("Section %i: size %i addr %p\n",
i, phdr[i].p_memsz, (void *)phdr[i].p_paddr);
/* We map this section of the file at its physical address. */
map_at(elf_fd, from_guest_phys(phdr[i].p_paddr),
phdr[i].p_offset, phdr[i].p_filesz);
/* The entry point is given in the ELF header. */
return ehdr->e_entry;
* A bzImage, unlike an ELF file, is not meant to be loaded. You're supposed
* to jump into it and it will unpack itself. We used to have to perform some
* hairy magic because the unpacking code scared me.
* Fortunately, Jeremy Fitzhardinge convinced me it wasn't that hard and wrote
* a small patch to jump over the tricky bits in the Guest, so now we just read
* the funky header so we know where in the file to load, and away we go!
static unsigned long load_bzimage(int fd)
struct boot_params boot;
int r;
/* Modern bzImages get loaded at 1M. */
void *p = from_guest_phys(0x100000);
* Go back to the start of the file and read the header. It should be
* a Linux boot header (see Documentation/x86/boot.txt)
lseek(fd, 0, SEEK_SET);
read(fd, &boot, sizeof(boot));
/* Inside the setup_hdr, we expect the magic "HdrS" */
if (memcmp(&boot.hdr.header, "HdrS", 4) != 0)
errx(1, "This doesn't look like a bzImage to me");
/* Skip over the extra sectors of the header. */
lseek(fd, (boot.hdr.setup_sects+1) * 512, SEEK_SET);
/* Now read everything into memory. in nice big chunks. */
while ((r = read(fd, p, 65536)) > 0)
p += r;
/* Finally, code32_start tells us where to enter the kernel. */
return boot.hdr.code32_start;
* Loading the kernel is easy when it's a "vmlinux", but most kernels
* come wrapped up in the self-decompressing "bzImage" format. With a little
* work, we can load those, too.
static unsigned long load_kernel(int fd)
Elf32_Ehdr hdr;
/* Read in the first few bytes. */
if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr))
err(1, "Reading kernel");
/* If it's an ELF file, it starts with "\177ELF" */
if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
return map_elf(fd, &hdr);
/* Otherwise we assume it's a bzImage, and try to load it. */
return load_bzimage(fd);
* This is a trivial little helper to align pages. Andi Kleen hated it because
* it calls getpagesize() twice: "it's dumb code."
* Kernel guys get really het up about optimization, even when it's not
* necessary. I leave this code as a reaction against that.
static inline unsigned long page_align(unsigned long addr)
/* Add upwards and truncate downwards. */
return ((addr + getpagesize()-1) & ~(getpagesize()-1));
* An "initial ram disk" is a disk image loaded into memory along with the
* kernel which the kernel can use to boot from without needing any drivers.
* Most distributions now use this as standard: the initrd contains the code to
* load the appropriate driver modules for the current machine.
* Importantly, James Morris works for RedHat, and Fedora uses initrds for its
* kernels. He sent me this (and tells me when I break it).
static unsigned long load_initrd(const char *name, unsigned long mem)
int ifd;
struct stat st;
unsigned long len;
ifd = open_or_die(name, O_RDONLY);
/* fstat() is needed to get the file size. */
if (fstat(ifd, &st) < 0)
err(1, "fstat() on initrd '%s'", name);
* We map the initrd at the top of memory, but mmap wants it to be
* page-aligned, so we round the size up for that.
len = page_align(st.st_size);
map_at(ifd, from_guest_phys(mem - len), 0, st.st_size);
* Once a file is mapped, you can close the file descriptor. It's a
* little odd, but quite useful.
verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);
/* We return the initrd size. */
return len;
* Simple routine to roll all the commandline arguments together with spaces
* between them.
static void concat(char *dst, char *args[])
unsigned int i, len = 0;
for (i = 0; args[i]; i++) {
if (i) {
strcat(dst+len, " ");
strcpy(dst+len, args[i]);
len += strlen(args[i]);
/* In case it's empty. */
dst[len] = '\0';
* This is where we actually tell the kernel to initialize the Guest. We
* saw the arguments it expects when we looked at initialize() in lguest_user.c:
* the base of Guest "physical" memory, the top physical page to allow and the
* entry point for the Guest.
static void tell_kernel(unsigned long start)
unsigned long args[] = { LHREQ_INITIALIZE,
(unsigned long)guest_base,
guest_limit / getpagesize(), start };
verbose("Guest: %p - %p (%#lx)\n",
guest_base, guest_base + guest_limit, guest_limit);
lguest_fd = open_or_die("/dev/lguest", O_RDWR);
if (write(lguest_fd, args, sizeof(args)) < 0)
err(1, "Writing to /dev/lguest");
* Device Handling.
* When the Guest gives us a buffer, it sends an array of addresses and sizes.
* We need to make sure it's not trying to reach into the Launcher itself, so
* we have a convenient routine which checks it and exits with an error message
* if something funny is going on:
static void *_check_pointer(unsigned long addr, unsigned int size,
unsigned int line)
* Check if the requested address and size exceeds the allocated memory,
* or addr + size wraps around.
if ((addr + size) > guest_limit || (addr + size) < addr)
errx(1, "%s:%i: Invalid address %#lx", __FILE__, line, addr);
* We return a pointer for the caller's convenience, now we know it's
* safe to use.
return from_guest_phys(addr);
/* A macro which transparently hands the line number to the real function. */
#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
* Each buffer in the virtqueues is actually a chain of descriptors. This
* function returns the next descriptor in the chain, or vq->vring.num if we're
* at the end.
static unsigned next_desc(struct vring_desc *desc,
unsigned int i, unsigned int max)
unsigned int next;
/* If this descriptor says it doesn't chain, we're done. */
if (!(desc[i].flags & VRING_DESC_F_NEXT))
return max;
/* Check they're not leading us off end of descriptors. */
next = desc[i].next;
/* Make sure compiler knows to grab that: we don't want it changing! */
if (next >= max)
errx(1, "Desc next is %u", next);
return next;
* This actually sends the interrupt for this virtqueue, if we've used a
* buffer.
static void trigger_irq(struct virtqueue *vq)
unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
/* Don't inform them if nothing used. */
if (!vq->pending_used)
vq->pending_used = 0;
/* If they don't want an interrupt, don't send one... */
if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT) {
/* Send the Guest an interrupt tell them we used something up. */
if (write(lguest_fd, buf, sizeof(buf)) != 0)
err(1, "Triggering irq %i", vq->config.irq);
* This looks in the virtqueue for the first available buffer, and converts
* it to an iovec for convenient access. Since descriptors consist of some
* number of output then some number of input descriptors, it's actually two
* iovecs, but we pack them into one and note how many of each there were.
* This function waits if necessary, and returns the descriptor number found.
static unsigned wait_for_vq_desc(struct virtqueue *vq,
struct iovec iov[],
unsigned int *out_num, unsigned int *in_num)
unsigned int i, head, max;
struct vring_desc *desc;
u16 last_avail = lg_last_avail(vq);
/* There's nothing available? */
while (last_avail == vq->vring.avail->idx) {
u64 event;
* Since we're about to sleep, now is a good time to tell the
* Guest about what we've used up to now.
/* OK, now we need to know about added descriptors. */
vq->vring.used->flags &= ~VRING_USED_F_NO_NOTIFY;
* They could have slipped one in as we were doing that: make
* sure it's written, then check again.
if (last_avail != vq->vring.avail->idx) {
vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
/* Nothing new? Wait for eventfd to tell us they refilled. */
if (read(vq->eventfd, &event, sizeof(event)) != sizeof(event))
errx(1, "Event read failed?");
/* We don't need to be notified again. */
vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
/* Check it isn't doing very strange things with descriptor numbers. */
if ((u16)(vq->vring.avail->idx - last_avail) > vq->vring.num)
errx(1, "Guest moved used index from %u to %u",
last_avail, vq->vring.avail->idx);
* Make sure we read the descriptor number *after* we read the ring
* update; don't let the cpu or compiler change the order.
* Grab the next descriptor number they're advertising, and increment
* the index we've seen.
head = vq->vring.avail->ring[last_avail % vq->vring.num];
/* If their number is silly, that's a fatal mistake. */
if (head >= vq->vring.num)
errx(1, "Guest says index %u is available", head);
/* When we start there are none of either input nor output. */
*out_num = *in_num = 0;
max = vq->vring.num;
desc = vq->vring.desc;
i = head;
* We have to read the descriptor after we read the descriptor number,
* but there's a data dependency there so the CPU shouldn't reorder
* that: no rmb() required.
* If this is an indirect entry, then this buffer contains a descriptor
* table which we handle as if it's any normal descriptor chain.
if (desc[i].flags & VRING_DESC_F_INDIRECT) {
if (desc[i].len % sizeof(struct vring_desc))
errx(1, "Invalid size for indirect buffer table");
max = desc[i].len / sizeof(struct vring_desc);
desc = check_pointer(desc[i].addr, desc[i].len);
i = 0;
do {
/* Grab the first descriptor, and check it's OK. */
iov[*out_num + *in_num].iov_len = desc[i].len;
iov[*out_num + *in_num].iov_base
= check_pointer(desc[i].addr, desc[i].len);
/* If this is an input descriptor, increment that count. */
if (desc[i].flags & VRING_DESC_F_WRITE)
else {
* If it's an output descriptor, they're all supposed
* to come before any input descriptors.
if (*in_num)
errx(1, "Descriptor has out after in");
/* If we've got too many, that implies a descriptor loop. */
if (*out_num + *in_num > max)
errx(1, "Looped descriptor");
} while ((i = next_desc(desc, i, max)) != max);
return head;
* After we've used one of their buffers, we tell the Guest about it. Sometime
* later we'll want to send them an interrupt using trigger_irq(); note that
* wait_for_vq_desc() does that for us if it has to wait.
static void add_used(struct virtqueue *vq, unsigned int head, int len)
struct vring_used_elem *used;
* The virtqueue contains a ring of used buffers. Get a pointer to the
* next entry in that used ring.
used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
used->id = head;
used->len = len;
/* Make sure buffer is written before we update index. */
/* And here's the combo meal deal. Supersize me! */
static void add_used_and_trigger(struct virtqueue *vq, unsigned head, int len)
add_used(vq, head, len);
* The Console
* We associate some data with the console for our exit hack.
struct console_abort {
/* How many times have they hit ^C? */
int count;
/* When did they start? */
struct timeval start;
/* This is the routine which handles console input (ie. stdin). */
static void console_input(struct virtqueue *vq)
int len;
unsigned int head, in_num, out_num;
struct console_abort *abort = vq->dev->priv;
struct iovec iov[vq->vring.num];
/* Make sure there's a descriptor available. */
head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
if (out_num)
errx(1, "Output buffers in console in queue?");
/* Read into it. This is where we usually wait. */
len = readv(STDIN_FILENO, iov, in_num);
if (len <= 0) {
/* Ran out of input? */
warnx("Failed to get console input, ignoring console.");
* For simplicity, dying threads kill the whole Launcher. So
* just nap here.
for (;;)
/* Tell the Guest we used a buffer. */
add_used_and_trigger(vq, head, len);
* Three ^C within one second? Exit.
* This is such a hack, but works surprisingly well. Each ^C has to
* be in a buffer by itself, so they can't be too fast. But we check
* that we get three within about a second, so they can't be too
* slow.
if (len != 1 || ((char *)iov[0].iov_base)[0] != 3) {
abort->count = 0;
if (abort->count == 1)
gettimeofday(&abort->start, NULL);
else if (abort->count == 3) {
struct timeval now;
gettimeofday(&now, NULL);
/* Kill all Launcher processes with SIGINT, like normal ^C */
if (now.tv_sec <= abort->start.tv_sec+1)
kill(0, SIGINT);
abort->count = 0;
/* This is the routine which handles console output (ie. stdout). */
static void console_output(struct virtqueue *vq)
unsigned int head, out, in;
struct iovec iov[vq->vring.num];
/* We usually wait in here, for the Guest to give us something. */
head = wait_for_vq_desc(vq, iov, &out, &in);
if (in)
errx(1, "Input buffers in console output queue?");
/* writev can return a partial write, so we loop here. */
while (!iov_empty(iov, out)) {
int len = writev(STDOUT_FILENO, iov, out);
if (len <= 0) {
warn("Write to stdout gave %i (%d)", len, errno);
iov_consume(iov, out, NULL, len);
* We're finished with that buffer: if we're going to sleep,
* wait_for_vq_desc() will prod the Guest with an interrupt.
add_used(vq, head, 0);
* The Network
* Handling output for network is also simple: we get all the output buffers
* and write them to /dev/net/tun.
struct net_info {
int tunfd;
static void net_output(struct virtqueue *vq)
struct net_info *net_info = vq->dev->priv;
unsigned int head, out, in;
struct iovec iov[vq->vring.num];
/* We usually wait in here for the Guest to give us a packet. */
head = wait_for_vq_desc(vq, iov, &out, &in);
if (in)
errx(1, "Input buffers in net output queue?");
* Send the whole thing through to /dev/net/tun. It expects the exact
* same format: what a coincidence!
if (writev(net_info->tunfd, iov, out) < 0)
warnx("Write to tun failed (%d)?", errno);
* Done with that one; wait_for_vq_desc() will send the interrupt if
* all packets are processed.
add_used(vq, head, 0);
* Handling network input is a bit trickier, because I've tried to optimize it.
* First we have a helper routine which tells is if from this file descriptor
* (ie. the /dev/net/tun device) will block:
static bool will_block(int fd)
fd_set fdset;
struct timeval zero = { 0, 0 };
FD_SET(fd, &fdset);
return select(fd+1, &fdset, NULL, NULL, &zero) != 1;
* This handles packets coming in from the tun device to our Guest. Like all
* service routines, it gets called again as soon as it returns, so you don't
* see a while(1) loop here.
static void net_input(struct virtqueue *vq)
int len;
unsigned int head, out, in;
struct iovec iov[vq->vring.num];
struct net_info *net_info = vq->dev->priv;
* Get a descriptor to write an incoming packet into. This will also
* send an interrupt if they're out of descriptors.
head = wait_for_vq_desc(vq, iov, &out, &in);
if (out)
errx(1, "Output buffers in net input queue?");
* If it looks like we'll block reading from the tun device, send them
* an interrupt.
if (vq->pending_used && will_block(net_info->tunfd))
* Read in the packet. This is where we normally wait (when there's no
* incoming network traffic).
len = readv(net_info->tunfd, iov, in);
if (len <= 0)
warn("Failed to read from tun (%d).", errno);
* Mark that packet buffer as used, but don't interrupt here. We want
* to wait until we've done as much work as we can.
add_used(vq, head, len);
/* This is the helper to create threads: run the service routine in a loop. */
static int do_thread(void *_vq)
struct virtqueue *vq = _vq;
for (;;)
return 0;
* When a child dies, we kill our entire process group with SIGTERM. This
* also has the side effect that the shell restores the console for us!
static void kill_launcher(int signal)
kill(0, SIGTERM);
static void reset_device(struct device *dev)
struct virtqueue *vq;
verbose("Resetting device %s\n", dev->name);
/* Clear any features they've acked. */
memset(get_feature_bits(dev) + dev->feature_len, 0, dev->feature_len);
/* We're going to be explicitly killing threads, so ignore them. */
/* Zero out the virtqueues, get rid of their threads */
for (vq = dev->vq; vq; vq = vq->next) {
if (vq->thread != (pid_t)-1) {
kill(vq->thread, SIGTERM);
waitpid(vq->thread, NULL, 0);
vq->thread = (pid_t)-1;
memset(vq->vring.desc, 0,
vring_size(vq->config.num, LGUEST_VRING_ALIGN));
lg_last_avail(vq) = 0;
dev->running = false;
/* Now we care if threads die. */
signal(SIGCHLD, (void *)kill_launcher);
* This actually creates the thread which services the virtqueue for a device.
static void create_thread(struct virtqueue *vq)
* Create stack for thread. Since the stack grows upwards, we point
* the stack pointer to the end of this region.
char *stack = malloc(32768);
unsigned long args[] = { LHREQ_EVENTFD,
vq->config.pfn*getpagesize(), 0 };
/* Create a zero-initialized eventfd. */
vq->eventfd = eventfd(0, 0);
if (vq->eventfd < 0)
err(1, "Creating eventfd");
args[2] = vq->eventfd;
* Attach an eventfd to this virtqueue: it will go off when the Guest
* does an LHCALL_NOTIFY for this vq.
if (write(lguest_fd, &args, sizeof(args)) != 0)
err(1, "Attaching eventfd");
* CLONE_VM: because it has to access the Guest memory, and SIGCHLD so
* we get a signal if it dies.
vq->thread = clone(do_thread, stack + 32768, CLONE_VM | SIGCHLD, vq);
if (vq->thread == (pid_t)-1)
err(1, "Creating clone");
/* We close our local copy now the child has it. */
static void start_device(struct device *dev)
unsigned int i;
struct virtqueue *vq;
verbose("Device %s OK: offered", dev->name);
for (i = 0; i < dev->feature_len; i++)
verbose(" %02x", get_feature_bits(dev)[i]);
verbose(", accepted");
for (i = 0; i < dev->feature_len; i++)
verbose(" %02x", get_feature_bits(dev)
for (vq = dev->vq; vq; vq = vq->next) {
if (vq->service)
dev->running = true;
static void cleanup_devices(void)
struct device *dev;
for (dev =; dev; dev = dev->next)
/* If we saved off the original terminal settings, restore them now. */
if (orig_term.c_lflag & (ISIG|ICANON|ECHO))
tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
/* When the Guest tells us they updated the status field, we handle it. */
static void update_device_status(struct device *dev)
/* A zero status is a reset, otherwise it's a set of flags. */
if (dev->desc->status == 0)
else if (dev->desc->status & VIRTIO_CONFIG_S_FAILED) {
warnx("Device %s configuration FAILED", dev->name);
if (dev->running)
} else {
if (dev->running)
err(1, "Device %s features finalized twice", dev->name);
* This is the generic routine we call when the Guest uses LHCALL_NOTIFY. In
* particular, it's used to notify us of device status changes during boot.
static void handle_output(unsigned long addr)
struct device *i;
/* Check each device. */
for (i =; i; i = i->next) {
struct virtqueue *vq;
* Notifications to device descriptors mean they updated the
* device status.
if (from_guest_phys(addr) == i->desc) {
/* Devices should not be used before features are finalized. */
for (vq = i->vq; vq; vq = vq->next) {
if (addr != vq->config.pfn*getpagesize())
errx(1, "Notification on %s before setup!", i->name);
* Early console write is done using notify on a nul-terminated string
* in Guest memory. It's also great for hacking debugging messages
* into a Guest.
if (addr >= guest_limit)
errx(1, "Bad NOTIFY %#lx", addr);
write(STDOUT_FILENO, from_guest_phys(addr),
strnlen(from_guest_phys(addr), guest_limit - addr));
* Device Setup
* All devices need a descriptor so the Guest knows it exists, and a "struct
* device" so the Launcher can keep track of it. We have common helper
* routines to allocate and manage them.
* The layout of the device page is a "struct lguest_device_desc" followed by a
* number of virtqueue descriptors, then two sets of feature bits, then an
* array of configuration bytes. This routine returns the configuration
* pointer.
static u8 *device_config(const struct device *dev)
return (void *)(dev->desc + 1)
+ dev->num_vq * sizeof(struct lguest_vqconfig)
+ dev->feature_len * 2;
* This routine allocates a new "struct lguest_device_desc" from descriptor
* table page just above the Guest's normal memory. It returns a pointer to
* that descriptor.
static struct lguest_device_desc *new_dev_desc(u16 type)
struct lguest_device_desc d = { .type = type };
void *p;
/* Figure out where the next device config is, based on the last one. */
if (devices.lastdev)
p = device_config(devices.lastdev)
+ devices.lastdev->desc->config_len;
p = devices.descpage;
/* We only have one page for all the descriptors. */
if (p + sizeof(d) > (void *)devices.descpage + getpagesize())
errx(1, "Too many devices");
/* p might not be aligned, so we memcpy in. */
return memcpy(p, &d, sizeof(d));
* Each device descriptor is followed by the description of its virtqueues. We
* specify how many descriptors the virtqueue is to have.
static void add_virtqueue(struct device *dev, unsigned int num_descs,
void (*service)(struct virtqueue *))
unsigned int pages;
struct virtqueue **i, *vq = malloc(sizeof(*vq));
void *p;
/* First we need some memory for this virtqueue. */
pages = (vring_size(num_descs, LGUEST_VRING_ALIGN) + getpagesize() - 1)
/ getpagesize();
p = get_pages(pages);
/* Initialize the virtqueue */
vq->next = NULL;
vq->last_avail_idx = 0;
vq->dev = dev;
* This is the routine the service thread will run, and its Process ID
* once it's running.
vq->service = service;
vq->thread = (pid_t)-1;
/* Initialize the configuration. */
vq->config.num = num_descs;
vq->config.irq = devices.next_irq++;
vq->config.pfn = to_guest_phys(p) / getpagesize();
/* Initialize the vring. */
vring_init(&vq->vring, num_descs, p, LGUEST_VRING_ALIGN);
* Append virtqueue to this device's descriptor. We use
* device_config() to get the end of the device's current virtqueues;
* we check that we haven't added any config or feature information
* yet, otherwise we'd be overwriting them.
assert(dev->desc->config_len == 0 && dev->desc->feature_len == 0);
memcpy(device_config(dev), &vq->config, sizeof(vq->config));
verbose("Virtqueue page %#lx\n", to_guest_phys(p));
* Add to tail of list, so dev->vq is first vq, dev->vq->next is
* second.
for (i = &dev->vq; *i; i = &(*i)->next);
*i = vq;
* The first half of the feature bitmask is for us to advertise features. The
* second half is for the Guest to accept features.
static void add_feature(struct device *dev, unsigned bit)
u8 *features = get_feature_bits(dev);
/* We can't extend the feature bits once we've added config bytes */
if (dev->desc->feature_len <= bit / CHAR_BIT) {
assert(dev->desc->config_len == 0);
dev->feature_len = dev->desc->feature_len = (bit/CHAR_BIT) + 1;
features[bit / CHAR_BIT] |= (1 << (bit % CHAR_BIT));
* This routine sets the configuration fields for an existing device's
* descriptor. It only works for the last device, but that's OK because that's
* how we use it.
static void set_config(struct device *dev, unsigned len, const void *conf)
/* Check we haven't overflowed our single page. */
if (device_config(dev) + len > devices.descpage + getpagesize())
errx(1, "Too many devices");
/* Copy in the config information, and store the length. */
memcpy(device_config(dev), conf, len);
dev->desc->config_len = len;
/* Size must fit in config_len field (8 bits)! */
assert(dev->desc->config_len == len);
* This routine does all the creation and setup of a new device, including
* calling new_dev_desc() to allocate the descriptor and device memory. We
* don't actually start the service threads until later.
* See what I mean about userspace being boring?
static struct device *new_device(const char *name, u16 type)
struct device *dev = malloc(sizeof(*dev));
/* Now we populate the fields one at a time. */
dev->desc = new_dev_desc(type);
dev->name = name;
dev->vq = NULL;
dev->feature_len = 0;
dev->num_vq = 0;
dev->running = false;
dev->next = NULL;
* Append to device list. Prepending to a single-linked list is
* easier, but the user expects the devices to be arranged on the bus
* in command-line order. The first network device on the command line
* is eth0, the first block device /dev/vda, etc.
if (devices.lastdev)
devices.lastdev->next = dev;
else = dev;
devices.lastdev = dev;
return dev;
* Our first setup routine is the console. It's a fairly simple device, but
* UNIX tty handling makes it uglier than it could be.
static void setup_console(void)
struct device *dev;
/* If we can save the initial standard input settings... */
if (tcgetattr(STDIN_FILENO, &orig_term) == 0) {
struct termios term = orig_term;
* Then we turn off echo, line buffering and ^C etc: We want a
* raw input stream to the Guest.
term.c_lflag &= ~(ISIG|ICANON|ECHO);
tcsetattr(STDIN_FILENO, TCSANOW, &term);
dev = new_device("console", VIRTIO_ID_CONSOLE);
/* We store the console state in dev->priv, and initialize it. */
dev->priv = malloc(sizeof(struct console_abort));
((struct console_abort *)dev->priv)->count = 0;
* The console needs two virtqueues: the input then the output. When
* they put something the input queue, we make sure we're listening to
* stdin. When they put something in the output queue, we write it to
* stdout.
add_virtqueue(dev, VIRTQUEUE_NUM, console_input);
add_virtqueue(dev, VIRTQUEUE_NUM, console_output);
verbose("device %u: console\n", ++devices.device_num);
* Inter-guest networking is an interesting area. Simplest is to have a
* --sharenet=<name> option which opens or creates a named pipe. This can be
* used to send packets to another guest in a 1:1 manner.
* More sophisticated is to use one of the tools developed for project like UML
* to do networking.
* Faster is to do virtio bonding in kernel. Doing this 1:1 would be
* completely generic ("here's my vring, attach to your vring") and would work
* for any traffic. Of course, namespace and permissions issues need to be
* dealt with. A more sophisticated "multi-channel" virtio_net.c could hide
* multiple inter-guest channels behind one interface, although it would
* require some manner of hotplugging new virtio channels.
* Finally, we could use a virtio network switch in the kernel, ie. vhost.
static u32 str2ip(const char *ipaddr)
unsigned int b[4];
if (sscanf(ipaddr, "%u.%u.%u.%u", &b[0], &b[1], &b[2], &b[3]) != 4)
errx(1, "Failed to parse IP address '%s'", ipaddr);
return (b[0] << 24) | (b[1] << 16) | (b[2] << 8) | b[3];
static void str2mac(const char *macaddr, unsigned char mac[6])
unsigned int m[6];
if (sscanf(macaddr, "%02x:%02x:%02x:%02x:%02x:%02x",
&m[0], &m[1], &m[2], &m[3], &m[4], &m[5]) != 6)
errx(1, "Failed to parse mac address '%s'", macaddr);
mac[0] = m[0];
mac[1] = m[1];
mac[2] = m[2];
mac[3] = m[3];
mac[4] = m[4];
mac[5] = m[5];
* This code is "adapted" from libbridge: it attaches the Host end of the
* network device to the bridge device specified by the command line.
* This is yet another James Morris contribution (I'm an IP-level guy, so I
* dislike bridging), and I just try not to break it.
static void add_to_bridge(int fd, const char *if_name, const char *br_name)
int ifidx;
struct ifreq ifr;
if (!*br_name)
errx(1, "must specify bridge name");
ifidx = if_nametoindex(if_name);
if (!ifidx)
errx(1, "interface %s does not exist!", if_name);
strncpy(ifr.ifr_name, br_name, IFNAMSIZ);
ifr.ifr_name[IFNAMSIZ-1] = '\0';
ifr.ifr_ifindex = ifidx;
if (ioctl(fd, SIOCBRADDIF, &ifr) < 0)
err(1, "can't add %s to bridge %s", if_name, br_name);
* This sets up the Host end of the network device with an IP address, brings
* it up so packets will flow, the copies the MAC address into the hwaddr
* pointer.
static void configure_device(int fd, const char *tapif, u32 ipaddr)
struct ifreq ifr;
struct sockaddr_in sin;
memset(&ifr, 0, sizeof(ifr));
strcpy(ifr.ifr_name, tapif);
/* Don't read these incantations. Just cut & paste them like I did! */
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl(ipaddr);
memcpy(&ifr.ifr_addr, &sin, sizeof(sin));
if (ioctl(fd, SIOCSIFADDR, &ifr) != 0)
err(1, "Setting %s interface address", tapif);
ifr.ifr_flags = IFF_UP;
if (ioctl(fd, SIOCSIFFLAGS, &ifr) != 0)
err(1, "Bringing interface %s up", tapif);
static int get_tun_device(char tapif[IFNAMSIZ])
struct ifreq ifr;
int netfd;
/* Start with this zeroed. Messy but sure. */
memset(&ifr, 0, sizeof(ifr));
* We open the /dev/net/tun device and tell it we want a tap device. A
* tap device is like a tun device, only somehow different. To tell
* the truth, I completely blundered my way through this code, but it
* works now!
netfd = open_or_die("/dev/net/tun", O_RDWR);
ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
strcpy(ifr.ifr_name, "tap%d");
if (ioctl(netfd, TUNSETIFF, &ifr) != 0)
err(1, "configuring /dev/net/tun");
if (ioctl(netfd, TUNSETOFFLOAD,
err(1, "Could not set features for tun device");
* We don't need checksums calculated for packets coming in this
* device: trust us!
ioctl(netfd, TUNSETNOCSUM, 1);
memcpy(tapif, ifr.ifr_name, IFNAMSIZ);
return netfd;
* Our network is a Host<->Guest network. This can either use bridging or
* routing, but the principle is the same: it uses the "tun" device to inject
* packets into the Host as if they came in from a normal network card. We
* just shunt packets between the Guest and the tun device.
static void setup_tun_net(char *arg)
struct device *dev;
struct net_info *net_info = malloc(sizeof(*net_info));
int ipfd;
u32 ip = INADDR_ANY;
bool bridging = false;
char tapif[IFNAMSIZ], *p;
struct virtio_net_config conf;
net_info->tunfd = get_tun_device(tapif);
/* First we create a new network device. */
dev = new_device("net", VIRTIO_ID_NET);
dev->priv = net_info;
/* Network devices need a recv and a send queue, just like console. */
add_virtqueue(dev, VIRTQUEUE_NUM, net_input);
add_virtqueue(dev, VIRTQUEUE_NUM, net_output);
* We need a socket to perform the magic network ioctls to bring up the
* tap interface, connect to the bridge etc. Any socket will do!
if (ipfd < 0)
err(1, "opening IP socket");
/* If the command line was --tunnet=bridge:<name> do bridging. */
if (!strncmp(BRIDGE_PFX, arg, strlen(BRIDGE_PFX))) {
arg += strlen(BRIDGE_PFX);
bridging = true;
/* A mac address may follow the bridge name or IP address */
p = strchr(arg, ':');
if (p) {
str2mac(p+1, conf.mac);
add_feature(dev, VIRTIO_NET_F_MAC);
*p = '\0';
/* arg is now either an IP address or a bridge name */
if (bridging)
add_to_bridge(ipfd, tapif, arg);
ip = str2ip(arg);
/* Set up the tun device. */
configure_device(ipfd, tapif, ip);
/* Expect Guest to handle everything except UFO */
add_feature(dev, VIRTIO_NET_F_CSUM);
add_feature(dev, VIRTIO_NET_F_GUEST_CSUM);
add_feature(dev, VIRTIO_NET_F_GUEST_TSO4);
add_feature(dev, VIRTIO_NET_F_GUEST_TSO6);
add_feature(dev, VIRTIO_NET_F_GUEST_ECN);
add_feature(dev, VIRTIO_NET_F_HOST_TSO4);
add_feature(dev, VIRTIO_NET_F_HOST_TSO6);
add_feature(dev, VIRTIO_NET_F_HOST_ECN);
/* We handle indirect ring entries */
add_feature(dev, VIRTIO_RING_F_INDIRECT_DESC);
/* We're compliant with the damn spec. */
add_feature(dev, VIRTIO_F_ANY_LAYOUT);
set_config(dev, sizeof(conf), &conf);
/* We don't need the socket any more; setup is done. */
if (bridging)
verbose("device %u: tun %s attached to bridge: %s\n",
devices.device_num, tapif, arg);
verbose("device %u: tun %s: %s\n",
devices.device_num, tapif, arg);
/* This hangs off device->priv. */
struct vblk_info {
/* The size of the file. */
off64_t len;
/* The file descriptor for the file. */
int fd;
* The Disk
* The disk only has one virtqueue, so it only has one thread. It is really
* simple: the Guest asks for a block number and we read or write that position
* in the file.
* Before we serviced each virtqueue in a separate thread, that was unacceptably
* slow: the Guest waits until the read is finished before running anything
* else, even if it could have been doing useful work.
* We could have used async I/O, except it's reputed to suck so hard that
* characters actually go missing from your code when you try to use it.
static void blk_request(struct virtqueue *vq)
struct vblk_info *vblk = vq->dev->priv;
unsigned int head, out_num, in_num, wlen;
int ret, i;
u8 *in;
struct virtio_blk_outhdr out;
struct iovec iov[vq->vring.num];
off64_t off;
* Get the next request, where we normally wait. It triggers the
* interrupt to acknowledge previously serviced requests (if any).
head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
/* Copy the output header from the front of the iov (adjusts iov) */
iov_consume(iov, out_num, &out, sizeof(out));
/* Find and trim end of iov input array, for our status byte. */
in = NULL;
for (i = out_num + in_num - 1; i >= out_num; i--) {
if (iov[i].iov_len > 0) {
in = iov[i].iov_base + iov[i].iov_len - 1;
if (!in)
errx(1, "Bad virtblk cmd with no room for status");
* For historical reasons, block operations are expressed in 512 byte
* "sectors".
off = out.sector * 512;
* In general the virtio block driver is allowed to try SCSI commands.
* It'd be nice if we supported eject, for example, but we don't.
if (out.type & VIRTIO_BLK_T_SCSI_CMD) {
fprintf(stderr, "Scsi commands unsupported\n");
wlen = sizeof(*in);
} else if (out.type & VIRTIO_BLK_T_OUT) {
* Write
* Move to the right location in the block file. This can fail
* if they try to write past end.
if (lseek64(vblk->fd, off, SEEK_SET) != off)
err(1, "Bad seek to sector %llu", out.sector);
ret = writev(vblk->fd, iov, out_num);
verbose("WRITE to sector %llu: %i\n", out.sector, ret);
* Grr... Now we know how long the descriptor they sent was, we
* make sure they didn't try to write over the end of the block
* file (possibly extending it).
if (ret > 0 && off + ret > vblk->len) {
/* Trim it back to the correct length */
ftruncate64(vblk->fd, vblk->len);
/* Die, bad Guest, die. */
errx(1, "Write past end %llu+%u", off, ret);
wlen = sizeof(*in);
*in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
} else if (out.type & VIRTIO_BLK_T_FLUSH) {
/* Flush */
ret = fdatasync(vblk->fd);
verbose("FLUSH fdatasync: %i\n", ret);
wlen = sizeof(*in);
*in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
} else {
* Read
* Move to the right location in the block file. This can fail
* if they try to read past end.
if (lseek64(vblk->fd, off, SEEK_SET) != off)
err(1, "Bad seek to sector %llu", out.sector);
ret = readv(vblk->fd, iov + out_num, in_num);
if (ret >= 0) {
wlen = sizeof(*in) + ret;
} else {
wlen = sizeof(*in);
/* Finished that request. */
add_used(vq, head, wlen);
/*L:198 This actually sets up a virtual block device. */
static void setup_block_file(const char *filename)
struct device *dev;
struct vblk_info *vblk;
struct virtio_blk_config conf;
/* Creat the device. */
dev = new_device("block", VIRTIO_ID_BLOCK);
/* The device has one virtqueue, where the Guest places requests. */
add_virtqueue(dev, VIRTQUEUE_NUM, blk_request);
/* Allocate the room for our own bookkeeping */
vblk = dev->priv = malloc(sizeof(*vblk));
/* First we open the file and store the length. */
vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
vblk->len = lseek64(vblk->fd, 0, SEEK_END);
/* We support FLUSH. */
add_feature(dev, VIRTIO_BLK_F_FLUSH);
/* Tell Guest how many sectors this device has. */
conf.capacity = cpu_to_le64(vblk->len / 512);
* Tell Guest not to put in too many descriptors at once: two are used
* for the in and out elements.
add_feature(dev, VIRTIO_BLK_F_SEG_MAX);
conf.seg_max = cpu_to_le32(VIRTQUEUE_NUM - 2);
/* Don't try to put whole struct: we have 8 bit limit. */
set_config(dev, offsetof(struct virtio_blk_config, geometry), &conf);
verbose("device %u: virtblock %llu sectors\n",
++devices.device_num, le64_to_cpu(conf.capacity));
* Our random number generator device reads from /dev/random into the Guest's
* input buffers. The usual case is that the Guest doesn't want random numbers
* and so has no buffers although /dev/random is still readable, whereas
* console is the reverse.
* The same logic applies, however.
struct rng_info {
int rfd;
static void rng_input(struct virtqueue *vq)
int len;
unsigned int head, in_num, out_num, totlen = 0;
struct rng_info *rng_info = vq->dev->priv;
struct iovec iov[vq->vring.num];
/* First we need a buffer from the Guests's virtqueue. */
head = wait_for_vq_desc(vq, iov, &out_num, &in_num);
if (out_num)
errx(1, "Output buffers in rng?");
* Just like the console write, we loop to cover the whole iovec.
* In this case, short reads actually happen quite a bit.
while (!iov_empty(iov, in_num)) {
len = readv(rng_info->rfd, iov, in_num);
if (len <= 0)
err(1, "Read from /dev/random gave %i", len);
iov_consume(iov, in_num, NULL, len);
totlen += len;
/* Tell the Guest about the new input. */
add_used(vq, head, totlen);
* This creates a "hardware" random number device for the Guest.
static void setup_rng(void)
struct device *dev;
struct rng_info *rng_info = malloc(sizeof(*rng_info));
/* Our device's privat info simply contains the /dev/random fd. */
rng_info->rfd = open_or_die("/dev/random", O_RDONLY);
/* Create the new device. */
dev = new_device("rng", VIRTIO_ID_RNG);
dev->priv = rng_info;
/* The device has one virtqueue, where the Guest places inbufs. */
add_virtqueue(dev, VIRTQUEUE_NUM, rng_input);
verbose("device %u: rng\n", devices.device_num++);
/* That's the end of device setup. */
/*L:230 Reboot is pretty easy: clean up and exec() the Launcher afresh. */
static void __attribute__((noreturn)) restart_guest(void)
unsigned int i;
* Since we don't track all open fds, we simply close everything beyond
* stderr.
for (i = 3; i < FD_SETSIZE; i++)
/* Reset all the devices (kills all threads). */
execv(main_args[0], main_args);
err(1, "Could not exec %s", main_args[0]);
* Finally we reach the core of the Launcher which runs the Guest, serves
* its input and output, and finally, lays it to rest.
static void __attribute__((noreturn)) run_guest(void)
for (;;) {
unsigned long notify_addr;
int readval;
/* We read from the /dev/lguest device to run the Guest. */
readval = pread(lguest_fd, &notify_addr,
sizeof(notify_addr), cpu_id);
/* One unsigned long means the Guest did HCALL_NOTIFY */
if (readval == sizeof(notify_addr)) {
verbose("Notify on address %#lx\n", notify_addr);
/* ENOENT means the Guest died. Reading tells us why. */
} else if (errno == ENOENT) {
char reason[1024] = { 0 };
pread(lguest_fd, reason, sizeof(reason)-1, cpu_id);
errx(1, "%s", reason);
/* ERESTART means that we need to reboot the guest */
} else if (errno == ERESTART) {
/* Anything else means a bug or incompatible change. */
} else
err(1, "Running guest failed");
* This is the end of the Launcher. The good news: we are over halfway
* through! The bad news: the most fiendish part of the code still lies ahead
* of us.
* Are you ready? Take a deep breath and join me in the core of the Host, in
* "make Host".
static struct option opts[] = {
{ "verbose", 0, NULL, 'v' },
{ "tunnet", 1, NULL, 't' },
{ "block", 1, NULL, 'b' },
{ "rng", 0, NULL, 'r' },
{ "initrd", 1, NULL, 'i' },
{ "username", 1, NULL, 'u' },
{ "chroot", 1, NULL, 'c' },
{ NULL },
static void usage(void)
errx(1, "Usage: lguest [--verbose] "
"<mem-in-mb> vmlinux [args...]");
/*L:105 The main routine is where the real work begins: */
int main(int argc, char *argv[])
/* Memory, code startpoint and size of the (optional) initrd. */
unsigned long mem = 0, start, initrd_size = 0;
/* Two temporaries. */
int i, c;
/* The boot information for the Guest. */
struct boot_params *boot;
/* If they specify an initrd file to load. */
const char *initrd_name = NULL;
/* Password structure for initgroups/setres[gu]id */
struct passwd *user_details = NULL;
/* Directory to chroot to */
char *chroot_path = NULL;
/* Save the args: we "reboot" by execing ourselves again. */
main_args = argv;
* First we initialize the device list. We keep a pointer to the last
* device, and the next interrupt number to use for devices (1:
* remember that 0 is used by the timer).
devices.lastdev = NULL;
devices.next_irq = 1;
/* We're CPU 0. In fact, that's the only CPU possible right now. */
cpu_id = 0;
* We need to know how much memory so we can set up the device
* descriptor and memory pages for the devices as we parse the command
* line. So we quickly look through the arguments to find the amount
* of memory now.
for (i = 1; i < argc; i++) {
if (argv[i][0] != '-') {
mem = atoi(argv[i]) * 1024 * 1024;
* We start by mapping anonymous pages over all of
* guest-physical memory range. This fills it with 0,
* and ensures that the Guest won't be killed when it
* tries to access it.
guest_base = map_zeroed_pages(mem / getpagesize()
guest_limit = mem;
guest_max = mem + DEVICE_PAGES*getpagesize();
devices.descpage = get_pages(1);
/* The options are fairly straight-forward */
while ((c = getopt_long(argc, argv, "v", opts, NULL)) != EOF) {
switch (c) {
case 'v':
verbose = true;
case 't':
case 'b':
case 'r':
case 'i':
initrd_name = optarg;
case 'u':
user_details = getpwnam(optarg);
if (!user_details)
err(1, "getpwnam failed, incorrect username?");
case 'c':
chroot_path = optarg;
warnx("Unknown argument %s", argv[optind]);
* After the other arguments we expect memory and kernel image name,
* followed by command line arguments for the kernel.
if (optind + 2 > argc)
verbose("Guest base is at %p\n", guest_base);
/* We always have a console device */
/* Now we load the kernel */
start = load_kernel(open_or_die(argv[optind+1], O_RDONLY));
/* Boot information is stashed at physical address 0 */
boot = from_guest_phys(0);
/* Map the initrd image if requested (at top of physical memory) */
if (initrd_name) {
initrd_size = load_initrd(initrd_name, mem);
* These are the location in the Linux boot header where the
* start and size of the initrd are expected to be found.
boot->hdr.ramdisk_image = mem - initrd_size;
boot->hdr.ramdisk_size = initrd_size;
/* The bootloader type 0xFF means "unknown"; that's OK. */
boot->hdr.type_of_loader = 0xFF;
* The Linux boot header contains an "E820" memory map: ours is a
* simple, single region.
boot->e820_entries = 1;
boot->e820_map[0] = ((struct e820entry) { 0, mem, E820_RAM });
* The boot header contains a command line pointer: we put the command
* line after the boot header.
boot->hdr.cmd_line_ptr = to_guest_phys(boot + 1);
/* We use a simple helper to copy the arguments separated by spaces. */
concat((char *)(boot + 1), argv+optind+2);
/* Set kernel alignment to 16M (CONFIG_PHYSICAL_ALIGN) */
boot->hdr.kernel_alignment = 0x1000000;
/* Boot protocol version: 2.07 supports the fields for lguest. */
boot->hdr.version = 0x207;
/* The hardware_subarch value of "1" tells the Guest it's an lguest. */
boot->hdr.hardware_subarch = 1;
/* Tell the entry path not to try to reload segment registers. */
boot->hdr.loadflags |= KEEP_SEGMENTS;
/* We tell the kernel to initialize the Guest. */
/* Ensure that we terminate if a device-servicing child dies. */
signal(SIGCHLD, kill_launcher);
/* If we exit via err(), this kills all the threads, restores tty. */
/* If requested, chroot to a directory */
if (chroot_path) {
if (chroot(chroot_path) != 0)
err(1, "chroot(\"%s\") failed", chroot_path);
if (chdir("/") != 0)
err(1, "chdir(\"/\") failed");
verbose("chroot done\n");
/* If requested, drop privileges */
if (user_details) {
uid_t u;
gid_t g;
u = user_details->pw_uid;
g = user_details->pw_gid;
if (initgroups(user_details->pw_name, g) != 0)
err(1, "initgroups failed");
if (setresgid(g, g, g) != 0)
err(1, "setresgid failed");
if (setresuid(u, u, u) != 0)
err(1, "setresuid failed");
verbose("Dropping privileges completed\n");
/* Finally, run the Guest. This doesn't return. */
* Mastery is done: you now know everything I do.
* But surely you have seen code, features and bugs in your wanderings which
* you now yearn to attack? That is the real game, and I look forward to you
* patching and forking lguest into the Your-Name-Here-visor.
* Farewell, and good coding!
* Rusty Russell.