[9fans] THNX linux kernel

[9fans] THNX linux kernel

[ron minnich]

is now on sources, ...

ls -l /n/sources/contrib/rminnich/lguest/2.6.23-rc5.tbz2
--rw-rw-r-- M 204583 rminnich sys 236518451 Sep  4 23:52
/n/sources/contrib/rminnich/lguest/2.6.23-rc5.tbz2

It's a git tree, the branch is plan9c.

ron

Re: [9fans] THNX linux kernel

[cummij]

hi ron-

> is now on sources, ...
>
> ls -l /n/sources/contrib/rminnich/lguest/2.6.23-rc5.tbz2
> --rw-rw-r-- M 204583 rminnich sys 236518451 Sep  4 23:52
> /n/sources/contrib/rminnich/lguest/2.6.23-rc5.tbz2
>
> It's a git tree, the branch is plan9c.
>
> ron

ok, i'm in a bit over my head here, so bear with me...

i've been playing with the lguest stuff you put on sources, and had some
success.  the "canned" system works on my thinkpad t40.  i've been trying
to add some modules to the linux kernel (such as ath_pci for wireless),
and my ignorance is manifesting itself.

i rebuilt the kernel from 2.6.23-rc5.tbz2, and installed it into /boot
on the usb stick.  then i had to learn all about initrd (and initramfs)
and managed to get an initramfs file into /boot also.  this all seems
to work and i boot into the new kernel, run "runme" and start syslog;
all without apparent error.  the problem comes when i try to start lguest
with RUNLGUEST - i get the following:

lguest: Mmapping vmlinux seg 0 gave 0xffffffff not 0x100000: invalid argument
lguest: Mmapping vmlinux seg 1 gave 0xffffffff not 0x16e000: invalid argument
lguest: syscall 64 is not resolved!
lguest used greatest stack depth: 1580 bytes left

any idea what i should try next?  do i need to recompile a new "lguest?"

thanks a alot,

john cummings

Re: [9fans] THNX linux kernel

[ron minnich]

[-- Attachment #1: Type: text/plain, Size: 612 bytes --]

On 9/19/07, cummij@rpi.edu <cummij@rpi.edu> wrote:

>
> lguest: Mmapping vmlinux seg 0 gave 0xffffffff not 0x100000: invalid argument
> lguest: Mmapping vmlinux seg 1 gave 0xffffffff not 0x16e000: invalid argument
> lguest: syscall 64 is not resolved!
> lguest used greatest stack depth: 1580 bytes left

you need my patched lguest.c, which I have attached.

That kernel must not have my patches, hmm, I will put my latest kernel
tree onto sources in just a minute. It is rc6. It has some better
improvements in it from Rusty.

I may have to make clean in it as the tree is HUGE.

Thanks

ron

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: lguest.c --]
[-- Type: text/x-csrc; name="lguest.c", Size: 52912 bytes --]

/*P:100 This is the Launcher code, a simple program which lays out the
 * "physical" memory for the new Guest by mapping the kernel image and the
 * virtual devices, then reads repeatedly from /dev/lguest to run the Guest.
 *
 * The only trick: the Makefile links it at a high address so it will be clear
 * of the guest memory region.  It means that each Guest cannot have more than
 * about 2.5G of memory on a normally configured Host. :*/
#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <err.h>
#include <stdint.h>
#include <stdlib.h>
#include <elf.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <stdbool.h>
#include <errno.h>
#include <ctype.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <time.h>
#include <netinet/in.h>
#include <net/if.h>
#include <linux/sockios.h>
#include <linux/if_tun.h>
#include <sys/uio.h>
#include <termios.h>
#include <getopt.h>
#include <zlib.h>
/*L:110 We can ignore the 28 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 and the header we need uses them, so we define them
 * here.
 */
typedef unsigned long long u64;
typedef uint32_t u32;
typedef uint16_t u16;
typedef uint8_t u8;
#include "../../include/linux/lguest_launcher.h"
#include "../../include/asm-i386/e820.h"
/*:*/

#define PAGE_PRESENT 0x7 	/* Present, RW, Execute */
#define NET_PEERNUM 1
#define BRIDGE_PFX "bridge:"
#ifndef SIOCBRADDIF
#define SIOCBRADDIF	0x89a2		/* add interface to bridge      */
#endif

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

/* The pipe to send commands to the waker process */
static int waker_fd;
/* The top of guest physical memory. */
static u32 top;

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

	/* The descriptor page for the devices. */
	struct lguest_device_desc *descs;

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

/* The device structure describes a single device. */
struct device
{
	/* The linked-list pointer. */
	struct device *next;
	/* The descriptor for this device, as mapped into the Guest. */
	struct lguest_device_desc *desc;
	/* The memory page(s) of this device, if any.  Also mapped in Guest. */
	void *mem;

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

	/* If handle_output is set, it wants to be called when the Guest sends
	 * DMA to this key. */
	unsigned long watch_key;
	u32 (*handle_output)(int fd, const struct iovec *iov,
			     unsigned int num, struct device *me);

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

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

/* map_zeroed_pages() takes a (page-aligned) address and a number of pages. */
static void *map_zeroed_pages(unsigned long addr, unsigned int num)
{
	/* We cache the /dev/zero file-descriptor so we only open it once. */
	static int fd = -1;

	if (fd == -1)
		fd = open_or_die("/dev/zero", O_RDONLY);

	/* We use a private mapping (ie. if we write to the page, it will be
	 * copied), and obviously we insist that it be mapped where we ask. */
	if (mmap((void *)addr, getpagesize() * num,
		 PROT_READ|PROT_WRITE|PROT_EXEC, MAP_FIXED|MAP_PRIVATE, fd, 0)
	    != (void *)addr)
		err(1, "Mmaping %u pages of /dev/zero @%p", num, (void *)addr);

	/* Returning the address is just a courtesy: can simplify callers. */
	return (void *)addr;
}

/* To find out where to start we look for the magic Guest string, which marks
 * the code we see in lguest_asm.S.  This is a hack which we are currently
 * plotting to replace with the normal Linux entry point. */
static unsigned long entry_point(void *start, void *end,
				 unsigned long page_offset)
{
	void *p;

	/* The scan gives us the physical starting address.  We want the
	 * virtual address in this case, and fortunately, we already figured
	 * out the physical-virtual difference and passed it here in
	 * "page_offset". */
	for (p = start; p < end; p++)
		if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
			return (long)p + strlen("GenuineLguest") + page_offset;

	err(1, "Is this image a genuine lguest?");
}

/* 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.  The Guest kernel expects to be placed in memory at the physical
 * address, and the page tables set up so it will correspond to that virtual
 * address.  We return the difference between the virtual and physical
 * addresses in the "page_offset" pointer.
 *
 * We return the starting address. */
static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
			     unsigned long *page_offset)
{
	void *addr;
	Elf32_Phdr phdr[ehdr->e_phnum];
	unsigned int i;
	unsigned long start = -1UL, end = 0;

	/* Sanity checks 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");

	/* We don't know page_offset yet. */
	*page_offset = 0;

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

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

		/* We expect a simple linear address space: every segment must
		 * have the same difference between virtual (p_vaddr) and
		 * physical (p_paddr) address. */
		if (!*page_offset)
			*page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
		else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
			errx(1, "Page offset of section %i different", i);

		/* We track the first and last address we mapped, so we can
		 * tell entry_point() where to scan. */
		if (phdr[i].p_paddr < start)
			start = phdr[i].p_paddr;
		if (phdr[i].p_paddr + phdr[i].p_filesz > end)
			end = phdr[i].p_paddr + phdr[i].p_filesz;

		/* We map this section of the file at its physical address.  We
		 * map it read & write even if the header says this segment is
		 * read-only.  The kernel really wants to be writable: it
		 * patches its own instructions which would normally be
		 * read-only.
		 *
		 * MAP_PRIVATE means that the page won't be copied until a
		 * write is done to it.  This allows us to share much of the
		 * kernel memory between Guests. */
		addr = mmap((void *)phdr[i].p_paddr,
			    phdr[i].p_filesz,
			    PROT_READ|PROT_WRITE|PROT_EXEC,
			    MAP_FIXED|MAP_PRIVATE,
			    elf_fd, phdr[i].p_offset);
		if (addr != (void *)phdr[i].p_paddr)
			err(1, "Mmaping vmlinux seg %i gave %p not %p",
			    i, addr, (void *)phdr[i].p_paddr);
	}

	return entry_point((void *)start, (void *)end, *page_offset);
}

/*L:170 Prepare to be SHOCKED and AMAZED.  And possibly a trifle nauseated.
 *
 * We know that CONFIG_PAGE_OFFSET sets what virtual address the kernel expects
 * to be.  We don't know what that option was, but we can figure it out
 * approximately by looking at the addresses in the code.  I chose the common
 * case of reading a memory location into the %eax register:
 *
 *  movl <some-address>, %eax
 *
 * This gets encoded as five bytes: "0xA1 <4-byte-address>".  For example,
 * "0xA1 0x18 0x60 0x47 0xC0" reads the address 0xC0476018 into %eax.
 *
 * In this example can guess that the kernel was compiled with
 * CONFIG_PAGE_OFFSET set to 0xC0000000 (it's always a round number).  If the
 * kernel were larger than 16MB, we might see 0xC1 addresses show up, but our
 * kernel isn't that bloated yet.
 *
 * Unfortunately, x86 has variable-length instructions, so finding this
 * particular instruction properly involves writing a disassembler.  Instead,
 * we rely on statistics.  We look for "0xA1" and tally the different bytes
 * which occur 4 bytes later (the "0xC0" in our example above).  When one of
 * those bytes appears three times, we can be reasonably confident that it
 * forms the start of CONFIG_PAGE_OFFSET.
 *
 * This is amazingly reliable. */
static unsigned long intuit_page_offset(unsigned char *img, unsigned long len)
{
	unsigned int i, possibilities[256] = { 0 };

	for (i = 0; i + 4 < len; i++) {
		/* mov 0xXXXXXXXX,%eax */
		if (img[i] == 0xA1 && ++possibilities[img[i+4]] > 3)
			return (unsigned long)img[i+4] << 24;
	}
	errx(1, "could not determine page offset");
}

/*L:160 Unfortunately the entire ELF image isn't compressed: the segments
 * which need loading are extracted and compressed raw.  This denies us the
 * information we need to make a fully-general loader. */
static unsigned long unpack_bzimage(int fd, unsigned long *page_offset)
{
	gzFile f;
	int ret, len = 0;
	/* A bzImage always gets loaded at physical address 1M.  This is
	 * actually configurable as CONFIG_PHYSICAL_START, but as the comment
	 * there says, "Don't change this unless you know what you are doing".
	 * Indeed. */
	void *img = (void *)0x100000;

	/* gzdopen takes our file descriptor (carefully placed at the start of
	 * the GZIP header we found) and returns a gzFile. */
	f = gzdopen(fd, "rb");
	/* We read it into memory in 64k chunks until we hit the end. */
	while ((ret = gzread(f, img + len, 65536)) > 0)
		len += ret;
	if (ret < 0)
		err(1, "reading image from bzImage");

	verbose("Unpacked size %i addr %p\n", len, img);

	/* Without the ELF header, we can't tell virtual-physical gap.  This is
	 * CONFIG_PAGE_OFFSET, and people do actually change it.  Fortunately,
	 * I have a clever way of figuring it out from the code itself.  */
	*page_offset = intuit_page_offset(img, len);

	return entry_point(img, img + len, *page_offset);
}

/*L:150 A bzImage, unlike an ELF file, is not meant to be loaded.  You're
 * supposed to jump into it and it will unpack itself.  We can't do that
 * because the Guest can't run the unpacking code, and adding features to
 * lguest kills puppies, so we don't want to.
 *
 * The bzImage is formed by putting the decompressing code in front of the
 * compressed kernel code.  So we can simple scan through it looking for the
 * first "gzip" header, and start decompressing from there. */
static unsigned long load_bzimage(int fd, unsigned long *page_offset)
{
	unsigned char c;
	int state = 0;

	/* GZIP header is 0x1F 0x8B <method> <flags>... <compressed-by>. */
	while (read(fd, &c, 1) == 1) {
		switch (state) {
		case 0:
			if (c == 0x1F)
				state++;
			break;
		case 1:
			if (c == 0x8B)
				state++;
			else
				state = 0;
			break;
		case 2 ... 8:
			state++;
			break;
		case 9:
			/* Seek back to the start of the gzip header. */
			lseek(fd, -10, SEEK_CUR);
			/* One final check: "compressed under UNIX". */
			if (c != 0x03)
				state = -1;
			else
				return unpack_bzimage(fd, page_offset);
		}
	}
	errx(1, "Could not find kernel in bzImage");
}

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

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

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

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

	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);

	/* The length needs to be rounded up to a page size: mmap needs the
	 * address to be page aligned. */
	len = page_align(st.st_size);
	/* We map the initrd at the top of memory. */
	iaddr = mmap((void *)mem - len, st.st_size,
		     PROT_READ|PROT_EXEC|PROT_WRITE,
		     MAP_FIXED|MAP_PRIVATE, ifd, 0);
	if (iaddr != (void *)mem - len)
		err(1, "Mmaping initrd '%s' returned %p not %p",
		    name, iaddr, (void *)mem - len);
	/* Once a file is mapped, you can close the file descriptor.  It's a
	 * little odd, but quite useful. */
	close(ifd);
	verbose("mapped initrd %s size=%lu @ %p\n", name, st.st_size, iaddr);

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

/* Once we know how much memory we have, and the address the Guest kernel
 * expects, we can construct simple linear page tables which will get the Guest
 * far enough into the boot to create its own.
 *
 * We lay them out of the way, just below the initrd (which is why we need to
 * know its size). */
static unsigned long setup_pagetables(unsigned long mem,
				      unsigned long initrd_size,
				      unsigned long page_offset)
{
	u32 *pgdir, *linear;
	unsigned int mapped_pages, i, linear_pages;
	unsigned int ptes_per_page = getpagesize()/sizeof(u32);

	/* Ideally we map all physical memory starting at page_offset.
	 * However, if page_offset is 0xC0000000 we can only map 1G of physical
	 * (0xC0000000 + 1G overflows). */
	if (mem <= -page_offset)
		mapped_pages = mem/getpagesize();
	else
		mapped_pages = -page_offset/getpagesize();

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

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

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

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

	/* The top level points to the linear page table pages above.  The
	 * entry representing page_offset points to the first one, and they
	 * continue from there. */
	for (i = 0; i < mapped_pages; i += ptes_per_page) {
		pgdir[(i + page_offset/getpagesize())/ptes_per_page]
			= (((u32)linear + i*sizeof(u32)) | PAGE_PRESENT);
	}

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

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

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

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

/* 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 top physical page to allow, the top level pagetable, the entry point and
 * the page_offset constant for the Guest. */
static int tell_kernel(u32 pgdir, u32 start, u32 page_offset)
{
	u32 args[] = { LHREQ_INITIALIZE,
		       top/getpagesize(), pgdir, start, page_offset };
	int fd;

	fd = open_or_die("/dev/lguest", O_RDWR);
	if (write(fd, args, sizeof(args)) < 0)
		err(1, "Writing to /dev/lguest");

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

static void set_fd(int fd, struct device_list *devices)
{
	FD_SET(fd, &devices->infds);
	if (fd > devices->max_infd)
		devices->max_infd = fd;
}

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

	for (;;) {
		fd_set rfds = devices->infds;
		u32 args[] = { LHREQ_BREAK, 1 };

		/* Wait until input is ready from one of the devices. */
		select(devices->max_infd+1, &rfds, NULL, NULL, NULL);
		/* Is it a message from the Launcher? */
		if (FD_ISSET(pipefd, &rfds)) {
			int ignorefd;
			/* If read() returns 0, it means the Launcher has
			 * exited.  We silently follow. */
			if (read(pipefd, &ignorefd, sizeof(ignorefd)) == 0)
				exit(0);
			/* Otherwise it's telling us there's a problem with one
			 * of the devices, and we should ignore that file
			 * descriptor from now on. */
			FD_CLR(ignorefd, &devices->infds);
		} else /* Send LHREQ_BREAK command. */
			write(lguest_fd, args, sizeof(args));
	}
}

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

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

	if (child == 0) {
		/* Close the "writing" end of our copy of the pipe */
		close(pipefd[1]);
		wake_parent(pipefd[0], lguest_fd, device_list);
	}
	/* Close the reading end of our copy of the pipe. */
	close(pipefd[0]);

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

/*L:210
 * Device Handling.
 *
 * When the Guest sends DMA to us, it sends us 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 check it and exits with an error message
 * if something funny is going on:
 */
static void *_check_pointer(unsigned long addr, unsigned int size,
			    unsigned int line)
{
	/* We have to separately check addr and addr+size, because size could
	 * be huge and addr + size might wrap around. */
	if (addr >= top || addr + size >= top)
		errx(1, "%s:%i: Invalid address %li", __FILE__, line, addr);
	/* We return a pointer for the caller's convenience, now we know it's
	 * safe to use. */
	return (void *)addr;
}
/* A macro which transparently hands the line number to the real function. */
#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)

/* The Guest has given us the address of a "struct lguest_dma".  We check it's
 * OK and convert it to an iovec (which is a simple array of ptr/size
 * pairs). */
static u32 *dma2iov(unsigned long dma, struct iovec iov[], unsigned *num)
{
	unsigned int i;
	struct lguest_dma *udma;

	/* First we make sure that the array memory itself is valid. */
	udma = check_pointer(dma, sizeof(*udma));
	/* Now we check each element */
	for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
		/* A zero length ends the array. */
		if (!udma->len[i])
			break;

		iov[i].iov_base = check_pointer(udma->addr[i], udma->len[i]);
		iov[i].iov_len = udma->len[i];
	}
	*num = i;

	/* We return the pointer to where the caller should write the amount of
	 * the buffer used. */
	return &udma->used_len;
}

/* This routine gets a DMA buffer from the Guest for a given key, and converts
 * it to an iovec array.  It returns the interrupt the Guest wants when we're
 * finished, and a pointer to the "used_len" field to fill in. */
static u32 *get_dma_buffer(int fd, void *key,
			   struct iovec iov[], unsigned int *num, u32 *irq)
{
	u32 buf[] = { LHREQ_GETDMA, (u32)key };
	unsigned long udma;
	u32 *res;

	/* Ask the kernel for a DMA buffer corresponding to this key. */
	udma = write(fd, buf, sizeof(buf));
	/* They haven't registered any, or they're all used? */
	if (udma == (unsigned long)-1)
		return NULL;

	/* Convert it into our iovec array */
	res = dma2iov(udma, iov, num);
	/* The kernel stashes irq in ->used_len to get it out to us. */
	*irq = *res;
	/* Return a pointer to ((struct lguest_dma *)udma)->used_len. */
	return res;
}

/* This is a convenient routine to send the Guest an interrupt. */
static void trigger_irq(int fd, u32 irq)
{
	u32 buf[] = { LHREQ_IRQ, irq };
	if (write(fd, buf, sizeof(buf)) != 0)
		err(1, "Triggering irq %i", irq);
}

/* This simply sets up an iovec array where we can put data to be discarded.
 * This happens when the Guest doesn't want or can't handle the input: we have
 * to get rid of it somewhere, and if we bury it in the ceiling space it will
 * start to smell after a week. */
static void discard_iovec(struct iovec *iov, unsigned int *num)
{
	static char discard_buf[1024];
	*num = 1;
	iov->iov_base = discard_buf;
	iov->iov_len = sizeof(discard_buf);
}

/* Here is the input terminal setting we save, and the routine to restore them
 * on exit so the user can see what they type next. */
static struct termios orig_term;
static void restore_term(void)
{
	tcsetattr(STDIN_FILENO, TCSANOW, &orig_term);
}

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

/* This is the routine which handles console input (ie. stdin). */
static bool handle_console_input(int fd, struct device *dev)
{
	u32 irq = 0, *lenp;
	int len;
	unsigned int num;
	struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
	struct console_abort *abort = dev->priv;

	/* First we get the console buffer from the Guest.  The key is dev->mem
	 * which was set to 0 in setup_console(). */
	lenp = get_dma_buffer(fd, dev->mem, iov, &num, &irq);
	if (!lenp) {
		/* If it's not ready for input, warn and set up to discard. */
		warn("console: no dma buffer!");
		discard_iovec(iov, &num);
	}

	/* This is why we convert to iovecs: the readv() call uses them, and so
	 * it reads straight into the Guest's buffer. */
	len = readv(dev->fd, iov, num);
	if (len <= 0) {
		/* This implies that the console is closed, is /dev/null, or
		 * something went terribly wrong.  We still go through the rest
		 * of the logic, though, especially the exit handling below. */
		warnx("Failed to get console input, ignoring console.");
		len = 0;
	}

	/* If we read the data into the Guest, fill in the length and send the
	 * interrupt. */
	if (lenp) {
		*lenp = len;
		trigger_irq(fd, irq);
	}

	/* Three ^C within one second?  Exit.
	 *
	 * This is such a hack, but works surprisingly well.  Each ^C has to be
	 * in a buffer by itself, so they can't be too fast.  But we check that
	 * we get three within about a second, so they can't be too slow. */
	if (len == 1 && ((char *)iov[0].iov_base)[0] == 3) {
		if (!abort->count++)
			gettimeofday(&abort->start, NULL);
		else if (abort->count == 3) {
			struct timeval now;
			gettimeofday(&now, NULL);
			if (now.tv_sec <= abort->start.tv_sec+1) {
				u32 args[] = { LHREQ_BREAK, 0 };
				/* Close the fd so Waker will know it has to
				 * exit. */
				close(waker_fd);
				/* Just in case waker is blocked in BREAK, send
				 * unbreak now. */
				write(fd, args, sizeof(args));
				exit(2);
			}
			abort->count = 0;
		}
	} else
		/* Any other key resets the abort counter. */
		abort->count = 0;

	/* Now, if we didn't read anything, put the input terminal back and
	 * return failure (meaning, don't call us again). */
	if (!len) {
		restore_term();
		return false;
	}
	/* Everything went OK! */
	return true;
}

/* Handling console output is much simpler than input. */
static u32 handle_console_output(int fd, const struct iovec *iov,
				 unsigned num, struct device*dev)
{
	/* Whatever the Guest sends, write it to standard output.  Return the
	 * number of bytes written. */
	return writev(STDOUT_FILENO, iov, num);
}

/* Guest->Host network output is also pretty easy. */
static u32 handle_tun_output(int fd, const struct iovec *iov,
			     unsigned num, struct device *dev)
{
	/* We put a flag in the "priv" pointer of the network device, and set
	 * it as soon as we see output.  We'll see why in handle_tun_input() */
	*(bool *)dev->priv = true;
	/* Whatever packet the Guest sent us, write it out to the tun
	 * device. */
	return writev(dev->fd, iov, num);
}

/* This matches the peer_key() in lguest_net.c.  The key for any given slot
 * is the address of the network device's page plus 4 * the slot number. */
static unsigned long peer_offset(unsigned int peernum)
{
	return 4 * peernum;
}

/* This is where we handle a packet coming in from the tun device */
static bool handle_tun_input(int fd, struct device *dev)
{
	u32 irq = 0, *lenp;
	int len;
	unsigned num;
	struct iovec iov[LGUEST_MAX_DMA_SECTIONS];

	/* First we get a buffer the Guest has bound to its key. */
	lenp = get_dma_buffer(fd, dev->mem+peer_offset(NET_PEERNUM), iov, &num,
			      &irq);
	if (!lenp) {
		/* Now, it's expected that if we try to send a packet too
		 * early, the Guest won't be ready yet.  This is why we set a
		 * flag when the Guest sends its first packet.  If it's sent a
		 * packet we assume it should be ready to receive them.
		 *
		 * Actually, this is what the status bits in the descriptor are
		 * for: we should *use* them.  FIXME! */
		if (*(bool *)dev->priv)
			warn("network: no dma buffer!");
		discard_iovec(iov, &num);
	}

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

	/* Write the used_len, and trigger the interrupt for the Guest */
	if (lenp) {
		*lenp = len;
		trigger_irq(fd, irq);
	}
	verbose("tun input packet len %i [%02x %02x] (%s)\n", len,
		((u8 *)iov[0].iov_base)[0], ((u8 *)iov[0].iov_base)[1],
		lenp ? "sent" : "discarded");
	/* All good. */
	return true;
}

/* The last device handling routine is block output: the Guest has sent a DMA
 * to the block device.  It will have placed the command it wants in the
 * "struct lguest_block_page". */
static u32 handle_block_output(int fd, const struct iovec *iov,
			       unsigned num, struct device *dev)
{
	struct lguest_block_page *p = dev->mem;
	u32 irq, *lenp;
	unsigned int len, reply_num;
	struct iovec reply[LGUEST_MAX_DMA_SECTIONS];
	off64_t device_len, off = (off64_t)p->sector * 512;

	/* First we extract the device length from the dev->priv pointer. */
	device_len = *(off64_t *)dev->priv;

	/* We first check that the read or write is within the length of the
	 * block file. */
	if (off >= device_len)
		err(1, "Bad offset %llu vs %llu", off, device_len);
	/* Move to the right location in the block file.  This shouldn't fail,
	 * but best to check. */
	if (lseek64(dev->fd, off, SEEK_SET) != off)
		err(1, "Bad seek to sector %i", p->sector);

	verbose("Block: %s at offset %llu\n", p->type ? "WRITE" : "READ", off);

	/* They were supposed to bind a reply buffer at key equal to the start
	 * of the block device memory.  We need this to tell them when the
	 * request is finished. */
	lenp = get_dma_buffer(fd, dev->mem, reply, &reply_num, &irq);
	if (!lenp)
		err(1, "Block request didn't give us a dma buffer");

	if (p->type) {
		/* A write request.  The DMA they sent contained the data, so
		 * write it out. */
		len = writev(dev->fd, iov, num);
		/* Grr... Now we know how long the "struct lguest_dma" they
		 * sent was, we make sure they didn't try to write over the end
		 * of the block file (possibly extending it). */
		if (off + len > device_len) {
			/* Trim it back to the correct length */
			ftruncate(dev->fd, device_len);
			/* Die, bad Guest, die. */
			errx(1, "Write past end %llu+%u", off, len);
		}
		/* The reply length is 0: we just send back an empty DMA to
		 * interrupt them and tell them the write is finished. */
		*lenp = 0;
	} else {
		/* A read request.  They sent an empty DMA to start the
		 * request, and we put the read contents into the reply
		 * buffer. */
		len = readv(dev->fd, reply, reply_num);
		*lenp = len;
	}

	/* The result is 1 (done), 2 if there was an error (short read or
	 * write). */
	p->result = 1 + (p->bytes != len);
	/* Now tell them we've used their reply buffer. */
	trigger_irq(fd, irq);

	/* We're supposed to return the number of bytes of the output buffer we
	 * used.  But the block device uses the "result" field instead, so we
	 * don't bother. */
	return 0;
}

/* This is the generic routine we call when the Guest sends some DMA out. */
static void handle_output(int fd, unsigned long dma, unsigned long key,
			  struct device_list *devices)
{
	struct device *i;
	u32 *lenp;
	struct iovec iov[LGUEST_MAX_DMA_SECTIONS];
	unsigned num = 0;

	/* Convert the "struct lguest_dma" they're sending to a "struct
	 * iovec". */
	lenp = dma2iov(dma, iov, &num);

	/* Check each device: if they expect output to this key, tell them to
	 * handle it. */
	for (i = devices->dev; i; i = i->next) {
		if (i->handle_output && key == i->watch_key) {
			/* We write the result straight into the used_len field
			 * for them. */
			*lenp = i->handle_output(fd, iov, num, i);
			return;
		}
	}

	/* This can happen: the kernel sends any SEND_DMA which doesn't match
	 * another Guest to us.  It could be that another Guest just left a
	 * network, for example.  But it's unusual. */
	warnx("Pending dma %p, key %p", (void *)dma, (void *)key);
}

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

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

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

		/* Otherwise, call the device(s) which have readable
		 * file descriptors and a method of handling them.  */
		for (i = devices->dev; i; i = i->next) {
			if (i->handle_input && FD_ISSET(i->fd, &fds)) {
				/* If handle_input() returns false, it means we
				 * should no longer service it.
				 * handle_console_input() does this. */
				if (!i->handle_input(fd, i)) {
					/* Clear it from the set of input file
					 * descriptors kept at the head of the
					 * device list. */
					FD_CLR(i->fd, &devices->infds);
					/* Tell waker to ignore it too... */
					write(waker_fd, &i->fd, sizeof(i->fd));
				}
			}
		}
	}
}

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

	for (i = 0; i < LGUEST_MAX_DEVICES; i++) {
		if (!descs[i].type) {
			descs[i].type = type;
			descs[i].features = features;
			descs[i].num_pages = num_pages;
			/* If they said the device needs memory, we allocate
			 * that now, bumping up the top of Guest memory. */
			if (num_pages) {
				map_zeroed_pages(top, num_pages);
				descs[i].pfn = top/getpagesize();
				top += num_pages*getpagesize();
			}
			return &descs[i];
		}
	}
	errx(1, "too many devices");
}

/* This monster routine does all the creation and setup of a new device,
 * including caling new_dev_desc() to allocate the descriptor and device
 * memory. */
static struct device *new_device(struct device_list *devices,
				 u16 type, u16 num_pages, u16 features,
				 int fd,
				 bool (*handle_input)(int, struct device *),
				 unsigned long watch_off,
				 u32 (*handle_output)(int,
						      const struct iovec *,
						      unsigned,
						      struct device *))
{
	struct device *dev = malloc(sizeof(*dev));

	/* Append to device list.  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/lgba, etc. */
	*devices->lastdev = dev;
	dev->next = NULL;
	devices->lastdev = &dev->next;

	/* Now we populate the fields one at a time. */
	dev->fd = fd;
	/* If we have an input handler for this file descriptor, then we add it
	 * to the device_list's fdset and maxfd. */
	if (handle_input)
		set_fd(dev->fd, devices);
	dev->desc = new_dev_desc(devices->descs, type, features, num_pages);
	dev->mem = (void *)(dev->desc->pfn * getpagesize());
	dev->handle_input = handle_input;
	dev->watch_key = (unsigned long)dev->mem + watch_off;
	dev->handle_output = handle_output;
	return dev;
}

/* 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(struct device_list *devices)
{
	struct device *dev;

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

	/* We don't currently require any memory for the console, so we ask for
	 * 0 pages. */
	dev = new_device(devices, LGUEST_DEVICE_T_CONSOLE, 0, 0,
			 STDIN_FILENO, handle_console_input,
			 LGUEST_CONSOLE_DMA_KEY, handle_console_output);
	/* 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;
	verbose("device %p: console\n",
		(void *)(dev->desc->pfn * getpagesize()));
}

/* Setting up a block file is also fairly straightforward. */
static void setup_block_file(const char *filename, struct device_list *devices)
{
	int fd;
	struct device *dev;
	off64_t *device_len;
	struct lguest_block_page *p;

	/* We open with O_LARGEFILE because otherwise we get stuck at 2G.  We
	 * open with O_DIRECT because otherwise our benchmarks go much too
	 * fast. */
	fd = open_or_die(filename, O_RDWR|O_LARGEFILE|O_DIRECT);

	/* We want one page, and have no input handler (the block file never
	 * has anything interesting to say to us).  Our timing will be quite
	 * random, so it should be a reasonable randomness source. */
	dev = new_device(devices, LGUEST_DEVICE_T_BLOCK, 1,
			 LGUEST_DEVICE_F_RANDOMNESS,
			 fd, NULL, 0, handle_block_output);

	/* We store the device size in the private area */
	device_len = dev->priv = malloc(sizeof(*device_len));
	/* This is the safe way of establishing the size of our device: it
	 * might be a normal file or an actual block device like /dev/hdb. */
	*device_len = lseek64(fd, 0, SEEK_END);

	/* The device memory is a "struct lguest_block_page".  It's zeroed
	 * already, we just need to put in the device size.  Block devices
	 * think in sectors (ie. 512 byte chunks), so we translate here. */
	p = dev->mem;
	p->num_sectors = *device_len/512;
	verbose("device %p: block %i sectors\n",
		(void *)(dev->desc->pfn * getpagesize()), p->num_sectors);
}

/*
 * Network Devices.
 *
 * Setting up network devices is quite a pain, because we have three types.
 * First, we have the inter-Guest network.  This is a file which is mapped into
 * the address space of the Guests who are on the network.  Because it is a
 * shared mapping, the same page underlies all the devices, and they can send
 * DMA to each other.
 *
 * Remember from our network driver, the Guest is told what slot in the page it
 * is to use.  We use exclusive fnctl locks to reserve a slot.  If another
 * Guest is using a slot, the lock will fail and we try another.  Because fnctl
 * locks are cleaned up automatically when we die, this cleverly means that our
 * reservation on the slot will vanish if we crash. */
static unsigned int find_slot(int netfd, const char *filename)
{
	struct flock fl;

	fl.l_type = F_WRLCK;
	fl.l_whence = SEEK_SET;
	fl.l_len = 1;
	/* Try a 1 byte lock in each possible position number */
	for (fl.l_start = 0;
	     fl.l_start < getpagesize()/sizeof(struct lguest_net);
	     fl.l_start++) {
		/* If we succeed, return the slot number. */
		if (fcntl(netfd, F_SETLK, &fl) == 0)
			return fl.l_start;
	}
	errx(1, "No free slots in network file %s", filename);
}

/* This function sets up the network file */
static void setup_net_file(const char *filename,
			   struct device_list *devices)
{
	int netfd;
	struct device *dev;

	/* We don't use open_or_die() here: for friendliness we create the file
	 * if it doesn't already exist. */
	netfd = open(filename, O_RDWR, 0);
	if (netfd < 0) {
		if (errno == ENOENT) {
			netfd = open(filename, O_RDWR|O_CREAT, 0600);
			if (netfd >= 0) {
				/* If we succeeded, initialize the file with a
				 * blank page. */
				char page[getpagesize()];
				memset(page, 0, sizeof(page));
				write(netfd, page, sizeof(page));
			}
		}
		if (netfd < 0)
			err(1, "cannot open net file '%s'", filename);
	}

	/* We need 1 page, and the features indicate the slot to use and that
	 * no checksum is needed.  We never touch this device again; it's
	 * between the Guests on the network, so we don't register input or
	 * output handlers. */
	dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
			 find_slot(netfd, filename)|LGUEST_NET_F_NOCSUM,
			 -1, NULL, 0, NULL);

	/* Map the shared file. */
	if (mmap(dev->mem, getpagesize(), PROT_READ|PROT_WRITE,
			 MAP_FIXED|MAP_SHARED, netfd, 0) != dev->mem)
			err(1, "could not mmap '%s'", filename);
	verbose("device %p: shared net %s, peer %i\n",
		(void *)(dev->desc->pfn * getpagesize()), filename,
		dev->desc->features & ~LGUEST_NET_F_NOCSUM);
}
/*:*/

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

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

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

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

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

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

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

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

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

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

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

	/* We create the net device with 1 page, using the features field of
	 * the descriptor to tell the Guest it is in slot 1 (NET_PEERNUM), and
	 * that the device has fairly random timing.  We do *not* specify
	 * LGUEST_NET_F_NOCSUM: these packets can reach the real world.
	 *
	 * We will put our MAC address is slot 0 for the Guest to see, so
	 * it will send packets to us using the key "peer_offset(0)": */
	dev = new_device(devices, LGUEST_DEVICE_T_NET, 1,
			 NET_PEERNUM|LGUEST_DEVICE_F_RANDOMNESS, netfd,
			 handle_tun_input, peer_offset(0), handle_tun_output);

	/* We keep a flag which says whether we've seen packets come out from
	 * this network device. */
	dev->priv = malloc(sizeof(bool));
	*(bool *)dev->priv = false;

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

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

	/* We are peer 0, ie. first slot, so we hand dev->mem to this routine
	 * to write the MAC address at the start of the device memory.  */
	configure_device(ipfd, ifr.ifr_name, ip, dev->mem);

	/* Set "promisc" bit: we want every single packet if we're going to
	 * bridge to other machines (and otherwise it doesn't matter). */
	*((u8 *)dev->mem) |= 0x1;

	close(ipfd);

	verbose("device %p: tun net %u.%u.%u.%u\n",
		(void *)(dev->desc->pfn * getpagesize()),
		(u8)(ip>>24), (u8)(ip>>16), (u8)(ip>>8), (u8)ip);
	if (br_name)
		verbose("attached to bridge: %s\n", br_name);
}
/* That's the end of device setup. */

/*L:220 Finally we reach the core of the Launcher, which runs the Guest, serves
 * its input and output, and finally, lays it to rest. */
static void __attribute__((noreturn))
run_guest(int lguest_fd, struct device_list *device_list)
{
	for (;;) {
		u32 args[] = { LHREQ_BREAK, 0 };
		unsigned long arr[2];
		int readval;

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

		/* The read can only really return sizeof(arr) (the Guest did a
		 * SEND_DMA to us), or an error. */

		/* For a successful read, arr[0] is the address of the "struct
		 * lguest_dma", and arr[1] is the key the Guest sent to. */
		if (readval == sizeof(arr)) {
			handle_output(lguest_fd, arr[0], arr[1], device_list);
			continue;
		/* ENOENT means the Guest died.  Reading tells us why. */
		} else if (errno == ENOENT) {
			char reason[1024] = { 0 };
			read(lguest_fd, reason, sizeof(reason)-1);
			errx(1, "%s", reason);
		/* EAGAIN means the waker wanted us to look at some input.
		 * Anything else means a bug or incompatible change. */
		} else if (errno != EAGAIN)
			err(1, "Running guest failed");

		/* Service input, then unset the BREAK which releases
		 * the Waker. */
		handle_input(lguest_fd, device_list);
		if (write(lguest_fd, args, sizeof(args)) < 0)
			err(1, "Resetting break");
	}
}
/*
 * This is the end of the Launcher.
 *
 * But wait!  We've seen I/O from the Launcher, and we've seen I/O from the
 * Drivers.  If we were to see the Host kernel I/O code, our understanding
 * would be complete... :*/

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

/*L:100 The Launcher code itself takes us out into userspace, that scary place
 * where pointers run wild and free!  Unfortunately, like most userspace
 * programs, it's quite boring (which is why everyone like 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 binary sits up high, usually starting at address 0xB8000000.
 * Everything below this is the "physical" memory for the Guest.  For example,
 * if the Guest were to write a "1" at physical address 0, we would see a "1"
 * in the Launcher at "(int *)0".  Guest physical == Launcher virtual.
 *
 * This can be tough to get your head around, but usually it just means that we
 * don't need to do any conversion when the Guest gives us it's "physical"
 * addresses.
 */
int main(int argc, char *argv[])
{
	/* Memory, top-level pagetable, code startpoint, PAGE_OFFSET and size
	 * of the (optional) initrd. */
	unsigned long mem = 0, pgdir, start, page_offset, initrd_size = 0;
	/* A temporary and the /dev/lguest file descriptor. */
	int i, c, lguest_fd;
	/* The list of Guest devices, based on command line arguments. */
	struct device_list device_list;
	/* The boot information for the Guest: at guest-physical address 0. */
	void *boot = (void *)0;
	/* If they specify an initrd file to load. */
	const char *initrd_name = NULL;

	/* First we initialize the device list.  Since console and network
	 * device receive input from a file descriptor, we keep an fdset
	 * (infds) and the maximum fd number (max_infd) with the head of the
	 * list.  We also keep a pointer to the last device, for easy appending
	 * to the list. */
	device_list.max_infd = -1;
	device_list.dev = NULL;
	device_list.lastdev = &device_list.dev;
	FD_ZERO(&device_list.infds);

	/* We need to know how much memory so we can 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 = top = atoi(argv[i]) * 1024 * 1024;
			device_list.descs = map_zeroed_pages(top, 1);
			top += getpagesize();
			break;
		}
	}

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

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

	/* 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. */
	map_zeroed_pages(0, mem / getpagesize());

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

	/* Map the initrd image if requested (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. */
		*(unsigned long *)(boot+0x218) = mem - initrd_size;
		*(unsigned long *)(boot+0x21c) = initrd_size;
		/* The bootloader type 0xFF means "unknown"; that's OK. */
		*(unsigned char *)(boot+0x210) = 0xFF;
	}

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

	/* The Linux boot header contains an "E820" memory map: ours is a
	 * simple, single region. */
	*(char*)(boot+E820NR) = 1;
	*((struct e820entry *)(boot+E820MAP))
		= ((struct e820entry) { 0, mem, E820_RAM });
	/* The boot header contains a command line pointer: we put the command
	 * line after the boot header (at address 4096) */
	*(void **)(boot + 0x228) = boot + 4096;
	concat(boot + 4096, argv+optind+2);

	/* The guest type value of "1" tells the Guest it's under lguest. */
	*(int *)(boot + 0x23c) = 1;

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

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

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

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