/*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-x86/e820_32.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 */ ftruncate64(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. */