Documentation / lguest / lguest.c

Based on kernel version 2.6.39.1. Page generated on 2011-06-03 13:47 EST.

	/*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 opens /dev/lguest to tell the kernel about the Guest and
	 * control it.
	:*/
	#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/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>
	
	#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"
	/*L:110
	 * We can ignore the 42 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;
	/*:*/
	
	#define PAGE_PRESENT 0x7 	/* Present, RW, Execute */
	#define BRIDGE_PFX "bridge:"
	#ifndef SIOCBRADDIF
	#define SIOCBRADDIF	0x89a2		/* add interface to bridge      */
	#endif
	/* 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
	
	/*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 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;
	
		/* Does Guest want an intrrupt on empty? */
		bool irq_on_empty;
	
		/* 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 mb() __asm__ __volatile__("" : : : "memory")
	
	/*
	 * Convert an iovec element to the given type.
	 *
	 * This is a fairly ugly trick: we need to know the size of the type and
	 * alignment requirement to check the pointer is kosher.  It's also nice to
	 * have the name of the type in case we report failure.
	 *
	 * Typing those three things all the time is cumbersome and error prone, so we
	 * have a macro which sets them all up and passes to the real function.
	 */
	#define convert(iov, type) \
		((type *)_convert((iov), sizeof(type), __alignof__(type), #type))
	
	static void *_convert(struct iovec *iov, size_t size, size_t align,
			      const char *name)
	{
		if (iov->iov_len != size)
			errx(1, "Bad iovec size %zu for %s", iov->iov_len, name);
		if ((unsigned long)iov->iov_base % align != 0)
			errx(1, "Bad alignment %p for %s", iov->iov_base, name);
		return iov->iov_base;
	}
	
	/* 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, 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;
			iov[i].iov_base += used;
			iov[i].iov_len -= used;
			len -= used;
		}
		assert(len == 0);
	}
	
	/* 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);
	}
	
	/*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 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);
	}
	
	/*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 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),
			    PROT_NONE, MAP_PRIVATE, fd, 0);
	
		if (addr == MAP_FAILED)
			err(1, "Mmapping %u pages of /dev/zero", num);
	
		if (mprotect(addr + getpagesize(), getpagesize() * num,
			     PROT_READ|PROT_WRITE) == -1)
			err(1, "mprotect rw %u pages failed", num);
	
		/*
		 * One neat mmap feature is that you can close the fd, and it
		 * stays mapped.
		 */
		close(fd);
	
		/* 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,
			 MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
			return;
	
		/* 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)
				continue;
	
			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;
	}
	
	/*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 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/i386/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;
	}
	
	/*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 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));
	}
	
	/*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;
	
		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.
		 */
		close(ifd);
		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, " ");
				len++;
			}
			strcpy(dst+len, args[i]);
			len += strlen(args[i]);
		}
		/* In case it's empty. */
		dst[len] = '\0';
	}
	
	/*L:185
	 * 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");
	}
	/*:*/
	
	/*L:200
	 * 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! */
		wmb();
	
		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)
			return;
		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) {
			/* ... unless they've asked us to force one on empty. */
			if (!vq->dev->irq_on_empty
			    || lg_last_avail(vq) != vq->vring.avail->idx)
				return;
		}
	
		/* 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.
			 */
			trigger_irq(vq);
	
			/* 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.
			 */
			mb();
			if (last_avail != vq->vring.avail->idx) {
				vq->vring.used->flags |= VRING_USED_F_NO_NOTIFY;
				break;
			}
	
			/* 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);
	
		/*
		 * 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];
		lg_last_avail(vq)++;
	
		/* 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;
	
		/*
		 * 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)
				(*in_num)++;
			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");
				(*out_num)++;
			}
	
			/* 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. */
		wmb();
		vq->vring.used->idx++;
		vq->pending_used++;
	}
	
	/* 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);
		trigger_irq(vq);
	}
	
	/*
	 * 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 (;;)
				pause();
		}
	
		/* 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;
			return;
		}
	
		abort->count++;
		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)
				err(1, "Write to stdout gave %i", len);
			iov_consume(iov, out, 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)
			errx(1, "Write to tun failed?");
	
		/*
		 * 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_ZERO(&fdset);
		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))
			trigger_irq(vq);
	
		/*
		 * 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)
			err(1, "Failed to read from tun.");
	
		/*
		 * 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 (;;)
			vq->service(vq);
		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. */
		signal(SIGCHLD, SIG_IGN);
	
		/* 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);
	}
	
	/*L:216
	 * 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. */
		close(vq->eventfd);
	}
	
	static bool accepted_feature(struct device *dev, unsigned int bit)
	{
		const u8 *features = get_feature_bits(dev) + dev->feature_len;
	
		if (dev->feature_len < bit / CHAR_BIT)
			return false;
		return features[bit / CHAR_BIT] & (1 << (bit % CHAR_BIT));
	}
	
	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)
				[dev->feature_len+i]);
	
		dev->irq_on_empty = accepted_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
	
		for (vq = dev->vq; vq; vq = vq->next) {
			if (vq->service)
				create_thread(vq);
		}
		dev->running = true;
	}
	
	static void cleanup_devices(void)
	{
		struct device *dev;
	
		for (dev = devices.dev; dev; dev = dev->next)
			reset_device(dev);
	
		/* 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)
			reset_device(dev);
		else if (dev->desc->status & VIRTIO_CONFIG_S_FAILED) {
			warnx("Device %s configuration FAILED", dev->name);
			if (dev->running)
				reset_device(dev);
		} else if (dev->desc->status & VIRTIO_CONFIG_S_DRIVER_OK) {
			if (!dev->running)
				start_device(dev);
		}
	}
	
	/*L:215
	 * 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 = devices.dev; i; i = i->next) {
			struct virtqueue *vq;
	
			/*
			 * Notifications to device descriptors mean they updated the
			 * device status.
			 */
			if (from_guest_phys(addr) == i->desc) {
				update_device_status(i);
				return;
			}
	
			/*
			 * Devices *can* be used before status is set to DRIVER_OK.
			 * The original plan was that they would never do this: they
			 * would always finish setting up their status bits before
			 * actually touching the virtqueues.  In practice, we allowed
			 * them to, and they do (eg. the disk probes for partition
			 * tables as part of initialization).
			 *
			 * If we see this, we start the device: once it's running, we
			 * expect the device to catch all the notifications.
			 */
			for (vq = i->vq; vq; vq = vq->next) {
				if (addr != vq->config.pfn*getpagesize())
					continue;
				if (i->running)
					errx(1, "Notification on running %s", i->name);
				/* This just calls create_thread() for each virtqueue */
				start_device(i);
				return;
			}
		}
	
		/*
		 * 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));
	}
	
	/*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 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;
		else
			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));
		dev->num_vq++;
		dev->desc->num_vq++;
	
		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;
	
		/*
		 * 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
			devices.dev = 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);
	}
	/*:*/
	
	/*M:010
	 * 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 sopisticated 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 implement a virtio network switch in the kernel.
	:*/
	
	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,
			  TUN_F_CSUM|TUN_F_TSO4|TUN_F_TSO6|TUN_F_TSO_ECN) != 0)
			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;
	}
	
	/*L:195
	 * 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!
		 */
		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))) {
			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);
		else
			ip = str2ip(arg);
	
		/* Set up the tun device. */
		configure_device(ipfd, tapif, ip);
	
		add_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
		/* 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);
		set_config(dev, sizeof(conf), &conf);
	
		/* We don't need the socket any more; setup is done. */
		close(ipfd);
	
		devices.device_num++;
	
		if (bridging)
			verbose("device %u: tun %s attached to bridge: %s\n",
				devices.device_num, tapif, arg);
		else
			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;
	
	};
	
	/*L:210
	 * 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;
		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);
	
		/*
		 * Every block request should contain at least one output buffer
		 * (detailing the location on disk and the type of request) and one
		 * input buffer (to hold the result).
		 */
		if (out_num == 0 || in_num == 0)
			errx(1, "Bad virtblk cmd %u out=%u in=%u",
			     head, out_num, in_num);
	
		out = convert(&iov[0], struct virtio_blk_outhdr);
		in = convert(&iov[out_num+in_num-1], u8);
		/*
		 * 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");
			*in = VIRTIO_BLK_S_UNSUPP;
			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+1, out_num-1);
			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+1, in_num-1);
			verbose("READ from sector %llu: %i\n", out->sector, ret);
			if (ret >= 0) {
				wlen = sizeof(*in) + ret;
				*in = VIRTIO_BLK_S_OK;
			} else {
				wlen = sizeof(*in);
				*in = VIRTIO_BLK_S_IOERR;
			}
		}
	
		/* 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));
	}
	
	/*L:211
	 * 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, len);
			totlen += len;
		}
	
		/* Tell the Guest about the new input. */
		add_used(vq, head, totlen);
	}
	
	/*L:199
	 * 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++)
			close(i);
	
		/* Reset all the devices (kills all threads). */
		cleanup_devices();
	
		execv(main_args[0], main_args);
		err(1, "Could not exec %s", main_args[0]);
	}
	
	/*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(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);
				handle_output(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) {
				restart_guest();
			/* Anything else means a bug or incompatible change. */
			} else
				err(1, "Running guest failed");
		}
	}
	/*L:240
	 * 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] "
		     "[--tunnet=(<ipaddr>:<macaddr>|bridge:<bridgename>:<macaddr>)\n"
		     "|--block=<filename>|--initrd=<filename>]...\n"
		     "<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()
							      + DEVICE_PAGES);
				guest_limit = mem;
				guest_max = mem + DEVICE_PAGES*getpagesize();
				devices.descpage = get_pages(1);
				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 't':
				setup_tun_net(optarg);
				break;
			case 'b':
				setup_block_file(optarg);
				break;
			case 'r':
				setup_rng();
				break;
			case 'i':
				initrd_name = optarg;
				break;
			case 'u':
				user_details = getpwnam(optarg);
				if (!user_details)
					err(1, "getpwnam failed, incorrect username?");
				break;
			case 'c':
				chroot_path = 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();
	
		verbose("Guest base is at %p\n", guest_base);
	
		/* We always have a console device */
		setup_console();
	
		/* 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);
	
		/* 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: this returns the open
		 * /dev/lguest file descriptor.
		 */
		tell_kernel(start);
	
		/* 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. */
		atexit(cleanup_devices);
	
		/* 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. */
		run_guest();
	}
	/*:*/
	
	/*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.
	 */

• [ lguest ]
• extract
• lguest.c
• lguest.txt
• Makefile
•  

---