The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/tools/lguest/lguest.c

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

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