util/oslib-posix.c - qemu - Git at Google

 /*
  * os-posix-lib.c
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  * Copyright (c) 2010 Red Hat, Inc.
  *
  * QEMU library functions on POSIX which are shared between QEMU and
  * the QEMU tools.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "qemu/osdep.h"
 #include <termios.h>

 #include <glib/gprintf.h>

 #include "sysemu/sysemu.h"
 #include "trace.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/madvise.h"
 #include "qemu/sockets.h"
 #include "qemu/thread.h"
 #include <libgen.h>
 #include "qemu/cutils.h"
 #include "qemu/compiler.h"
 #include "qemu/units.h"

 #ifdef CONFIG_LINUX
 #include <sys/syscall.h>
 #endif

 #ifdef __FreeBSD__
 #include <sys/thr.h>
 #include <sys/types.h>
 #include <sys/user.h>
 #include <libutil.h>
 #endif

 #ifdef __NetBSD__
 #include <lwp.h>
 #endif

 #ifdef __APPLE__
 #include <mach-o/dyld.h>
 #endif

 #ifdef __HAIKU__
 #include <kernel/image.h>
 #endif

 #include "qemu/mmap-alloc.h"

 #ifdef CONFIG_DEBUG_STACK_USAGE
 #include "qemu/error-report.h"
 #endif

 #define MAX_MEM_PREALLOC_THREAD_COUNT 16

 struct MemsetThread;

 typedef struct MemsetContext {
     bool all_threads_created;
     bool any_thread_failed;
     struct MemsetThread *threads;
     int num_threads;
 } MemsetContext;

 struct MemsetThread {
     char *addr;
     size_t numpages;
     size_t hpagesize;
     QemuThread pgthread;
     sigjmp_buf env;
     MemsetContext *context;
 };
 typedef struct MemsetThread MemsetThread;

 /* used by sigbus_handler() */
 static MemsetContext *sigbus_memset_context;
 struct sigaction sigbus_oldact;
 static QemuMutex sigbus_mutex;

 static QemuMutex page_mutex;
 static QemuCond page_cond;

 int qemu_get_thread_id(void)
 {
 #if defined(__linux__)
     return syscall(SYS_gettid);
 #elif defined(__FreeBSD__)
     /* thread id is up to INT_MAX */
     long tid;
     thr_self(&tid);
     return (int)tid;
 #elif defined(__NetBSD__)
     return _lwp_self();
 #elif defined(__OpenBSD__)
     return getthrid();
 #else
     return getpid();
 #endif
 }

 int qemu_daemon(int nochdir, int noclose)
 {
     return daemon(nochdir, noclose);
 }

 bool qemu_write_pidfile(const char *path, Error **errp)
 {
     int fd;
     char pidstr[32];

     while (1) {
         struct stat a, b;
         struct flock lock = {
             .l_type = F_WRLCK,
             .l_whence = SEEK_SET,
             .l_len = 0,
         };

         fd = qemu_create(path, O_WRONLY, S_IRUSR | S_IWUSR, errp);
         if (fd == -1) {
             return false;
         }

         if (fstat(fd, &b) < 0) {
             error_setg_errno(errp, errno, "Cannot stat file");
             goto fail_close;
         }

         if (fcntl(fd, F_SETLK, &lock)) {
             error_setg_errno(errp, errno, "Cannot lock pid file");
             goto fail_close;
         }

         /*
          * Now make sure the path we locked is the same one that now
          * exists on the filesystem.
          */
         if (stat(path, &a) < 0) {
             /*
              * PID file disappeared, someone else must be racing with
              * us, so try again.
              */
             close(fd);
             continue;
         }

         if (a.st_ino == b.st_ino) {
             break;
         }

         /*
          * PID file was recreated, someone else must be racing with
          * us, so try again.
          */
         close(fd);
     }

     if (ftruncate(fd, 0) < 0) {
         error_setg_errno(errp, errno, "Failed to truncate pid file");
         goto fail_unlink;
     }

     snprintf(pidstr, sizeof(pidstr), FMT_pid "\n", getpid());
     if (qemu_write_full(fd, pidstr, strlen(pidstr)) != strlen(pidstr)) {
         error_setg(errp, "Failed to write pid file");
         goto fail_unlink;
     }

     return true;

 fail_unlink:
     unlink(path);
 fail_close:
     close(fd);
     return false;
 }

 /* alloc shared memory pages */
 void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared,
                           bool noreserve)
 {
     const uint32_t qemu_map_flags = (shared ? QEMU_MAP_SHARED : 0) |
                                     (noreserve ? QEMU_MAP_NORESERVE : 0);
     size_t align = QEMU_VMALLOC_ALIGN;
     void *ptr = qemu_ram_mmap(-1, size, align, qemu_map_flags, 0);

     if (ptr == MAP_FAILED) {
         return NULL;
     }

     if (alignment) {
         *alignment = align;
     }

     trace_qemu_anon_ram_alloc(size, ptr);
     return ptr;
 }

 void qemu_anon_ram_free(void *ptr, size_t size)
 {
     trace_qemu_anon_ram_free(ptr, size);
     qemu_ram_munmap(-1, ptr, size);
 }

 void qemu_socket_set_block(int fd)
 {
     g_unix_set_fd_nonblocking(fd, false, NULL);
 }

 int qemu_socket_try_set_nonblock(int fd)
 {
     return g_unix_set_fd_nonblocking(fd, true, NULL) ? 0 : -errno;
 }

 void qemu_socket_set_nonblock(int fd)
 {
     int f;
     f = qemu_socket_try_set_nonblock(fd);
     assert(f == 0);
 }

 int socket_set_fast_reuse(int fd)
 {
     int val = 1, ret;

     ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                      (const char *)&val, sizeof(val));

     assert(ret == 0);

     return ret;
 }

 void qemu_set_cloexec(int fd)
 {
     int f;
     f = fcntl(fd, F_GETFD);
     assert(f != -1);
     f = fcntl(fd, F_SETFD, f | FD_CLOEXEC);
     assert(f != -1);
 }

 char *
 qemu_get_local_state_dir(void)
 {
     return get_relocated_path(CONFIG_QEMU_LOCALSTATEDIR);
 }

 void qemu_set_tty_echo(int fd, bool echo)
 {
     struct termios tty;

     tcgetattr(fd, &tty);

     if (echo) {
         tty.c_lflag |= ECHO | ECHONL | ICANON | IEXTEN;
     } else {
         tty.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN);
     }

     tcsetattr(fd, TCSANOW, &tty);
 }

 #ifdef CONFIG_LINUX
 static void sigbus_handler(int signal, siginfo_t *siginfo, void *ctx)
 #else /* CONFIG_LINUX */
 static void sigbus_handler(int signal)
 #endif /* CONFIG_LINUX */
 {
     int i;

     if (sigbus_memset_context) {
         for (i = 0; i < sigbus_memset_context->num_threads; i++) {
             MemsetThread *thread = &sigbus_memset_context->threads[i];

             if (qemu_thread_is_self(&thread->pgthread)) {
                 siglongjmp(thread->env, 1);
             }
         }
     }

 #ifdef CONFIG_LINUX
     /*
      * We assume that the MCE SIGBUS handler could have been registered. We
      * should never receive BUS_MCEERR_AO on any of our threads, but only on
      * the main thread registered for PR_MCE_KILL_EARLY. Further, we should not
      * receive BUS_MCEERR_AR triggered by action of other threads on one of
      * our threads. So, no need to check for unrelated SIGBUS when seeing one
      * for our threads.
      *
      * We will forward to the MCE handler, which will either handle the SIGBUS
      * or reinstall the default SIGBUS handler and reraise the SIGBUS. The
      * default SIGBUS handler will crash the process, so we don't care.
      */
     if (sigbus_oldact.sa_flags & SA_SIGINFO) {
         sigbus_oldact.sa_sigaction(signal, siginfo, ctx);
         return;
     }
 #endif /* CONFIG_LINUX */
     warn_report("os_mem_prealloc: unrelated SIGBUS detected and ignored");
 }

 static void *do_touch_pages(void *arg)
 {
     MemsetThread *memset_args = (MemsetThread *)arg;
     sigset_t set, oldset;
     int ret = 0;

     /*
      * On Linux, the page faults from the loop below can cause mmap_sem
      * contention with allocation of the thread stacks.  Do not start
      * clearing until all threads have been created.
      */
     qemu_mutex_lock(&page_mutex);
     while (!memset_args->context->all_threads_created) {
         qemu_cond_wait(&page_cond, &page_mutex);
     }
     qemu_mutex_unlock(&page_mutex);

     /* unblock SIGBUS */
     sigemptyset(&set);
     sigaddset(&set, SIGBUS);
     pthread_sigmask(SIG_UNBLOCK, &set, &oldset);

     if (sigsetjmp(memset_args->env, 1)) {
         ret = -EFAULT;
     } else {
         char *addr = memset_args->addr;
         size_t numpages = memset_args->numpages;
         size_t hpagesize = memset_args->hpagesize;
         size_t i;
         for (i = 0; i < numpages; i++) {
             /*
              * Read & write back the same value, so we don't
              * corrupt existing user/app data that might be
              * stored.
              *
              * 'volatile' to stop compiler optimizing this away
              * to a no-op
              */
             *(volatile char *)addr = *addr;
             addr += hpagesize;
         }
     }
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
     return (void *)(uintptr_t)ret;
 }

 static void *do_madv_populate_write_pages(void *arg)
 {
     MemsetThread *memset_args = (MemsetThread *)arg;
     const size_t size = memset_args->numpages * memset_args->hpagesize;
     char * const addr = memset_args->addr;
     int ret = 0;

     /* See do_touch_pages(). */
     qemu_mutex_lock(&page_mutex);
     while (!memset_args->context->all_threads_created) {
         qemu_cond_wait(&page_cond, &page_mutex);
     }
     qemu_mutex_unlock(&page_mutex);

     if (size && qemu_madvise(addr, size, QEMU_MADV_POPULATE_WRITE)) {
         ret = -errno;
     }
     return (void *)(uintptr_t)ret;
 }

 static inline int get_memset_num_threads(size_t hpagesize, size_t numpages,
                                          int smp_cpus)
 {
     long host_procs = sysconf(_SC_NPROCESSORS_ONLN);
     int ret = 1;

     if (host_procs > 0) {
         ret = MIN(MIN(host_procs, MAX_MEM_PREALLOC_THREAD_COUNT), smp_cpus);
     }

     /* Especially with gigantic pages, don't create more threads than pages. */
     ret = MIN(ret, numpages);
     /* Don't start threads to prealloc comparatively little memory. */
     ret = MIN(ret, MAX(1, hpagesize * numpages / (64 * MiB)));

     /* In case sysconf() fails, we fall back to single threaded */
     return ret;
 }

 static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
                            int smp_cpus, bool use_madv_populate_write)
 {
     static gsize initialized = 0;
     MemsetContext context = {
         .num_threads = get_memset_num_threads(hpagesize, numpages, smp_cpus),
     };
     size_t numpages_per_thread, leftover;
     void *(*touch_fn)(void *);
     int ret = 0, i = 0;
     char *addr = area;

     if (g_once_init_enter(&initialized)) {
         qemu_mutex_init(&page_mutex);
         qemu_cond_init(&page_cond);
         g_once_init_leave(&initialized, 1);
     }

     if (use_madv_populate_write) {
         /* Avoid creating a single thread for MADV_POPULATE_WRITE */
         if (context.num_threads == 1) {
             if (qemu_madvise(area, hpagesize * numpages,
                              QEMU_MADV_POPULATE_WRITE)) {
                 return -errno;
             }
             return 0;
         }
         touch_fn = do_madv_populate_write_pages;
     } else {
         touch_fn = do_touch_pages;
     }

     context.threads = g_new0(MemsetThread, context.num_threads);
     numpages_per_thread = numpages / context.num_threads;
     leftover = numpages % context.num_threads;
     for (i = 0; i < context.num_threads; i++) {
         context.threads[i].addr = addr;
         context.threads[i].numpages = numpages_per_thread + (i < leftover);
         context.threads[i].hpagesize = hpagesize;
         context.threads[i].context = &context;
         qemu_thread_create(&context.threads[i].pgthread, "touch_pages",
                            touch_fn, &context.threads[i],
                            QEMU_THREAD_JOINABLE);
         addr += context.threads[i].numpages * hpagesize;
     }

     if (!use_madv_populate_write) {
         sigbus_memset_context = &context;
     }

     qemu_mutex_lock(&page_mutex);
     context.all_threads_created = true;
     qemu_cond_broadcast(&page_cond);
     qemu_mutex_unlock(&page_mutex);

     for (i = 0; i < context.num_threads; i++) {
         int tmp = (uintptr_t)qemu_thread_join(&context.threads[i].pgthread);

         if (tmp) {
             ret = tmp;
         }
     }

     if (!use_madv_populate_write) {
         sigbus_memset_context = NULL;
     }
     g_free(context.threads);

     return ret;
 }

 static bool madv_populate_write_possible(char *area, size_t pagesize)
 {
     return !qemu_madvise(area, pagesize, QEMU_MADV_POPULATE_WRITE) ||
            errno != EINVAL;
 }

 void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
                      Error **errp)
 {
     static gsize initialized;
     int ret;
     size_t hpagesize = qemu_fd_getpagesize(fd);
     size_t numpages = DIV_ROUND_UP(memory, hpagesize);
     bool use_madv_populate_write;
     struct sigaction act;

     /*
      * Sense on every invocation, as MADV_POPULATE_WRITE cannot be used for
      * some special mappings, such as mapping /dev/mem.
      */
     use_madv_populate_write = madv_populate_write_possible(area, hpagesize);

     if (!use_madv_populate_write) {
         if (g_once_init_enter(&initialized)) {
             qemu_mutex_init(&sigbus_mutex);
             g_once_init_leave(&initialized, 1);
         }

         qemu_mutex_lock(&sigbus_mutex);
         memset(&act, 0, sizeof(act));
 #ifdef CONFIG_LINUX
         act.sa_sigaction = &sigbus_handler;
         act.sa_flags = SA_SIGINFO;
 #else /* CONFIG_LINUX */
         act.sa_handler = &sigbus_handler;
         act.sa_flags = 0;
 #endif /* CONFIG_LINUX */

         ret = sigaction(SIGBUS, &act, &sigbus_oldact);
         if (ret) {
             qemu_mutex_unlock(&sigbus_mutex);
             error_setg_errno(errp, errno,
                 "os_mem_prealloc: failed to install signal handler");
             return;
         }
     }

     /* touch pages simultaneously */
     ret = touch_all_pages(area, hpagesize, numpages, smp_cpus,
                           use_madv_populate_write);
     if (ret) {
         error_setg_errno(errp, -ret,
                          "os_mem_prealloc: preallocating memory failed");
     }

     if (!use_madv_populate_write) {
         ret = sigaction(SIGBUS, &sigbus_oldact, NULL);
         if (ret) {
             /* Terminate QEMU since it can't recover from error */
             perror("os_mem_prealloc: failed to reinstall signal handler");
             exit(1);
         }
         qemu_mutex_unlock(&sigbus_mutex);
     }
 }

 char *qemu_get_pid_name(pid_t pid)
 {
     char *name = NULL;

 #if defined(__FreeBSD__)
     /* BSDs don't have /proc, but they provide a nice substitute */
     struct kinfo_proc *proc = kinfo_getproc(pid);

     if (proc) {
         name = g_strdup(proc->ki_comm);
         free(proc);
     }
 #else
     /* Assume a system with reasonable procfs */
     char *pid_path;
     size_t len;

     pid_path = g_strdup_printf("/proc/%d/cmdline", pid);
     g_file_get_contents(pid_path, &name, &len, NULL);
     g_free(pid_path);
 #endif

     return name;
 }


 pid_t qemu_fork(Error **errp)
 {
     sigset_t oldmask, newmask;
     struct sigaction sig_action;
     int saved_errno;
     pid_t pid;

     /*
      * Need to block signals now, so that child process can safely
      * kill off caller's signal handlers without a race.
      */
     sigfillset(&newmask);
     if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) {
         error_setg_errno(errp, errno,
                          "cannot block signals");
         return -1;
     }

     pid = fork();
     saved_errno = errno;

     if (pid < 0) {
         /* attempt to restore signal mask, but ignore failure, to
          * avoid obscuring the fork failure */
         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
         error_setg_errno(errp, saved_errno,
                          "cannot fork child process");
         errno = saved_errno;
         return -1;
     } else if (pid) {
         /* parent process */

         /* Restore our original signal mask now that the child is
          * safely running. Only documented failures are EFAULT (not
          * possible, since we are using just-grabbed mask) or EINVAL
          * (not possible, since we are using correct arguments).  */
         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
     } else {
         /* child process */
         size_t i;

         /* Clear out all signal handlers from parent so nothing
          * unexpected can happen in our child once we unblock
          * signals */
         sig_action.sa_handler = SIG_DFL;
         sig_action.sa_flags = 0;
         sigemptyset(&sig_action.sa_mask);

         for (i = 1; i < NSIG; i++) {
             /* Only possible errors are EFAULT or EINVAL The former
              * won't happen, the latter we expect, so no need to check
              * return value */
             (void)sigaction(i, &sig_action, NULL);
         }

         /* Unmask all signals in child, since we've no idea what the
          * caller's done with their signal mask and don't want to
          * propagate that to children */
         sigemptyset(&newmask);
         if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) {
             Error *local_err = NULL;
             error_setg_errno(&local_err, errno,
                              "cannot unblock signals");
             error_report_err(local_err);
             _exit(1);
         }
     }
     return pid;
 }

 void *qemu_alloc_stack(size_t *sz)
 {
     void *ptr, *guardpage;
     int flags;
 #ifdef CONFIG_DEBUG_STACK_USAGE
     void *ptr2;
 #endif
     size_t pagesz = qemu_real_host_page_size();
 #ifdef _SC_THREAD_STACK_MIN
     /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
     long min_stack_sz = sysconf(_SC_THREAD_STACK_MIN);
     *sz = MAX(MAX(min_stack_sz, 0), *sz);
 #endif
     /* adjust stack size to a multiple of the page size */
     *sz = ROUND_UP(*sz, pagesz);
     /* allocate one extra page for the guard page */
     *sz += pagesz;

     flags = MAP_PRIVATE | MAP_ANONYMOUS;
 #if defined(MAP_STACK) && defined(__OpenBSD__)
     /* Only enable MAP_STACK on OpenBSD. Other OS's such as
      * Linux/FreeBSD/NetBSD have a flag with the same name
      * but have differing functionality. OpenBSD will SEGV
      * if it spots execution with a stack pointer pointing
      * at memory that was not allocated with MAP_STACK.
      */
     flags |= MAP_STACK;
 #endif

     ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, flags, -1, 0);
     if (ptr == MAP_FAILED) {
         perror("failed to allocate memory for stack");
         abort();
     }

 #if defined(HOST_IA64)
     /* separate register stack */
     guardpage = ptr + (((*sz - pagesz) / 2) & ~pagesz);
 #elif defined(HOST_HPPA)
     /* stack grows up */
     guardpage = ptr + *sz - pagesz;
 #else
     /* stack grows down */
     guardpage = ptr;
 #endif
     if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
         perror("failed to set up stack guard page");
         abort();
     }

 #ifdef CONFIG_DEBUG_STACK_USAGE
     for (ptr2 = ptr + pagesz; ptr2 < ptr + *sz; ptr2 += sizeof(uint32_t)) {
         *(uint32_t *)ptr2 = 0xdeadbeaf;
     }
 #endif

     return ptr;
 }

 #ifdef CONFIG_DEBUG_STACK_USAGE
 static __thread unsigned int max_stack_usage;
 #endif

 void qemu_free_stack(void *stack, size_t sz)
 {
 #ifdef CONFIG_DEBUG_STACK_USAGE
     unsigned int usage;
     void *ptr;

     for (ptr = stack + qemu_real_host_page_size(); ptr < stack + sz;
          ptr += sizeof(uint32_t)) {
         if (*(uint32_t *)ptr != 0xdeadbeaf) {
             break;
         }
     }
     usage = sz - (uintptr_t) (ptr - stack);
     if (usage > max_stack_usage) {
         error_report("thread %d max stack usage increased from %u to %u",
                      qemu_get_thread_id(), max_stack_usage, usage);
         max_stack_usage = usage;
     }
 #endif

     munmap(stack, sz);
 }

 /*
  * Disable CFI checks.
  * We are going to call a signal hander directly. Such handler may or may not
  * have been defined in our binary, so there's no guarantee that the pointer
  * used to set the handler is a cfi-valid pointer. Since the handlers are
  * stored in kernel memory, changing the handler to an attacker-defined
  * function requires being able to call a sigaction() syscall,
  * which is not as easy as overwriting a pointer in memory.
  */
 QEMU_DISABLE_CFI
 void sigaction_invoke(struct sigaction *action,
                       struct qemu_signalfd_siginfo *info)
 {
     siginfo_t si = {};
     si.si_signo = info->ssi_signo;
     si.si_errno = info->ssi_errno;
     si.si_code = info->ssi_code;

     /* Convert the minimal set of fields defined by POSIX.
      * Positive si_code values are reserved for kernel-generated
      * signals, where the valid siginfo fields are determined by
      * the signal number.  But according to POSIX, it is unspecified
      * whether SI_USER and SI_QUEUE have values less than or equal to
      * zero.
      */
     if (info->ssi_code == SI_USER || info->ssi_code == SI_QUEUE ||
         info->ssi_code <= 0) {
         /* SIGTERM, etc.  */
         si.si_pid = info->ssi_pid;
         si.si_uid = info->ssi_uid;
     } else if (info->ssi_signo == SIGILL || info->ssi_signo == SIGFPE ||
                info->ssi_signo == SIGSEGV || info->ssi_signo == SIGBUS) {
         si.si_addr = (void *)(uintptr_t)info->ssi_addr;
     } else if (info->ssi_signo == SIGCHLD) {
         si.si_pid = info->ssi_pid;
         si.si_status = info->ssi_status;
         si.si_uid = info->ssi_uid;
     }
     action->sa_sigaction(info->ssi_signo, &si, NULL);
 }

 size_t qemu_get_host_physmem(void)
 {
 #ifdef _SC_PHYS_PAGES
     long pages = sysconf(_SC_PHYS_PAGES);
     if (pages > 0) {
         if (pages > SIZE_MAX / qemu_real_host_page_size()) {
             return SIZE_MAX;
         } else {
             return pages * qemu_real_host_page_size();
         }
     }
 #endif
     return 0;
 }

 int qemu_msync(void *addr, size_t length, int fd)
 {
     size_t align_mask = ~(qemu_real_host_page_size() - 1);

     /**
      * There are no strict reqs as per the length of mapping
      * to be synced. Still the length needs to follow the address
      * alignment changes. Additionally - round the size to the multiple
      * of PAGE_SIZE
      */
     length += ((uintptr_t)addr & (qemu_real_host_page_size() - 1));
     length = (length + ~align_mask) & align_mask;

     addr = (void *)((uintptr_t)addr & align_mask);

     return msync(addr, length, MS_SYNC);
 }
	/*
	* os-posix-lib.c
	*
	* Copyright (c) 2003-2008 Fabrice Bellard
	* Copyright (c) 2010 Red Hat, Inc.
	*
	* QEMU library functions on POSIX which are shared between QEMU and
	* the QEMU tools.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "qemu/osdep.h"
	#include <termios.h>

	#include <glib/gprintf.h>

	#include "sysemu/sysemu.h"
	#include "trace.h"
	#include "qapi/error.h"
	#include "qemu/error-report.h"
	#include "qemu/madvise.h"
	#include "qemu/sockets.h"
	#include "qemu/thread.h"
	#include <libgen.h>
	#include "qemu/cutils.h"
	#include "qemu/compiler.h"
	#include "qemu/units.h"

	#ifdef CONFIG_LINUX
	#include <sys/syscall.h>
	#endif

	#ifdef __FreeBSD__
	#include <sys/thr.h>
	#include <sys/types.h>
	#include <sys/user.h>
	#include <libutil.h>
	#endif

	#ifdef __NetBSD__
	#include <lwp.h>
	#endif

	#ifdef __APPLE__
	#include <mach-o/dyld.h>
	#endif

	#ifdef __HAIKU__
	#include <kernel/image.h>
	#endif

	#include "qemu/mmap-alloc.h"

	#ifdef CONFIG_DEBUG_STACK_USAGE
	#include "qemu/error-report.h"
	#endif

	#define MAX_MEM_PREALLOC_THREAD_COUNT 16

	struct MemsetThread;

	typedef struct MemsetContext {
	bool all_threads_created;
	bool any_thread_failed;
	struct MemsetThread *threads;
	int num_threads;
	} MemsetContext;

	struct MemsetThread {
	char *addr;
	size_t numpages;
	size_t hpagesize;
	QemuThread pgthread;
	sigjmp_buf env;
	MemsetContext *context;
	};
	typedef struct MemsetThread MemsetThread;

	/* used by sigbus_handler() */
	static MemsetContext *sigbus_memset_context;
	struct sigaction sigbus_oldact;
	static QemuMutex sigbus_mutex;

	static QemuMutex page_mutex;
	static QemuCond page_cond;

	int qemu_get_thread_id(void)
	{
	#if defined(__linux__)
	return syscall(SYS_gettid);
	#elif defined(__FreeBSD__)
	/* thread id is up to INT_MAX */
	long tid;
	thr_self(&tid);
	return (int)tid;
	#elif defined(__NetBSD__)
	return _lwp_self();
	#elif defined(__OpenBSD__)
	return getthrid();
	#else
	return getpid();
	#endif
	}

	int qemu_daemon(int nochdir, int noclose)
	{
	return daemon(nochdir, noclose);
	}

	bool qemu_write_pidfile(const char path, Error *errp)
	{
	int fd;
	char pidstr[32];

	while (1) {
	struct stat a, b;
	struct flock lock = {
	.l_type = F_WRLCK,
	.l_whence = SEEK_SET,
	.l_len = 0,
	};

	fd = qemu_create(path, O_WRONLY, S_IRUSR \| S_IWUSR, errp);
	if (fd == -1) {
	return false;
	}

	if (fstat(fd, &b) < 0) {
	error_setg_errno(errp, errno, "Cannot stat file");
	goto fail_close;
	}

	if (fcntl(fd, F_SETLK, &lock)) {
	error_setg_errno(errp, errno, "Cannot lock pid file");
	goto fail_close;
	}

	/*
	* Now make sure the path we locked is the same one that now
	* exists on the filesystem.
	*/
	if (stat(path, &a) < 0) {
	/*
	* PID file disappeared, someone else must be racing with
	* us, so try again.
	*/
	close(fd);
	continue;
	}

	if (a.st_ino == b.st_ino) {
	break;
	}

	/*
	* PID file was recreated, someone else must be racing with
	* us, so try again.
	*/
	close(fd);
	}

	if (ftruncate(fd, 0) < 0) {
	error_setg_errno(errp, errno, "Failed to truncate pid file");
	goto fail_unlink;
	}

	snprintf(pidstr, sizeof(pidstr), FMT_pid "\n", getpid());
	if (qemu_write_full(fd, pidstr, strlen(pidstr)) != strlen(pidstr)) {
	error_setg(errp, "Failed to write pid file");
	goto fail_unlink;
	}

	return true;

	fail_unlink:
	unlink(path);
	fail_close:
	close(fd);
	return false;
	}

	/* alloc shared memory pages */
	void qemu_anon_ram_alloc(size_t size, uint64_t alignment, bool shared,
	bool noreserve)
	{
	const uint32_t qemu_map_flags = (shared ? QEMU_MAP_SHARED : 0) \|
	(noreserve ? QEMU_MAP_NORESERVE : 0);
	size_t align = QEMU_VMALLOC_ALIGN;
	void *ptr = qemu_ram_mmap(-1, size, align, qemu_map_flags, 0);

	if (ptr == MAP_FAILED) {
	return NULL;
	}

	if (alignment) {
	*alignment = align;
	}

	trace_qemu_anon_ram_alloc(size, ptr);
	return ptr;
	}

	void qemu_anon_ram_free(void *ptr, size_t size)
	{
	trace_qemu_anon_ram_free(ptr, size);
	qemu_ram_munmap(-1, ptr, size);
	}

	void qemu_socket_set_block(int fd)
	{
	g_unix_set_fd_nonblocking(fd, false, NULL);
	}

	int qemu_socket_try_set_nonblock(int fd)
	{
	return g_unix_set_fd_nonblocking(fd, true, NULL) ? 0 : -errno;
	}

	void qemu_socket_set_nonblock(int fd)
	{
	int f;
	f = qemu_socket_try_set_nonblock(fd);
	assert(f == 0);
	}

	int socket_set_fast_reuse(int fd)
	{
	int val = 1, ret;

	ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
	(const char *)&val, sizeof(val));

	assert(ret == 0);

	return ret;
	}

	void qemu_set_cloexec(int fd)
	{
	int f;
	f = fcntl(fd, F_GETFD);
	assert(f != -1);
	f = fcntl(fd, F_SETFD, f \| FD_CLOEXEC);
	assert(f != -1);
	}

	char *
	qemu_get_local_state_dir(void)
	{
	return get_relocated_path(CONFIG_QEMU_LOCALSTATEDIR);
	}

	void qemu_set_tty_echo(int fd, bool echo)
	{
	struct termios tty;

	tcgetattr(fd, &tty);

	if (echo) {
	tty.c_lflag \|= ECHO \| ECHONL \| ICANON \| IEXTEN;
	} else {
	tty.c_lflag &= ~(ECHO \| ECHONL \| ICANON \| IEXTEN);
	}

	tcsetattr(fd, TCSANOW, &tty);
	}

	#ifdef CONFIG_LINUX
	static void sigbus_handler(int signal, siginfo_t siginfo, void ctx)
	#else /* CONFIG_LINUX */
	static void sigbus_handler(int signal)
	#endif /* CONFIG_LINUX */
	{
	int i;

	if (sigbus_memset_context) {
	for (i = 0; i < sigbus_memset_context->num_threads; i++) {
	MemsetThread *thread = &sigbus_memset_context->threads[i];

	if (qemu_thread_is_self(&thread->pgthread)) {
	siglongjmp(thread->env, 1);
	}
	}
	}

	#ifdef CONFIG_LINUX
	/*
	* We assume that the MCE SIGBUS handler could have been registered. We
	* should never receive BUS_MCEERR_AO on any of our threads, but only on
	* the main thread registered for PR_MCE_KILL_EARLY. Further, we should not
	* receive BUS_MCEERR_AR triggered by action of other threads on one of
	* our threads. So, no need to check for unrelated SIGBUS when seeing one
	* for our threads.
	*
	* We will forward to the MCE handler, which will either handle the SIGBUS
	* or reinstall the default SIGBUS handler and reraise the SIGBUS. The
	* default SIGBUS handler will crash the process, so we don't care.
	*/
	if (sigbus_oldact.sa_flags & SA_SIGINFO) {
	sigbus_oldact.sa_sigaction(signal, siginfo, ctx);
	return;
	}
	#endif /* CONFIG_LINUX */
	warn_report("os_mem_prealloc: unrelated SIGBUS detected and ignored");
	}

	static void do_touch_pages(void arg)
	{
	MemsetThread memset_args = (MemsetThread )arg;
	sigset_t set, oldset;
	int ret = 0;

	/*
	* On Linux, the page faults from the loop below can cause mmap_sem
	* contention with allocation of the thread stacks. Do not start
	* clearing until all threads have been created.
	*/
	qemu_mutex_lock(&page_mutex);
	while (!memset_args->context->all_threads_created) {
	qemu_cond_wait(&page_cond, &page_mutex);
	}
	qemu_mutex_unlock(&page_mutex);

	/* unblock SIGBUS */
	sigemptyset(&set);
	sigaddset(&set, SIGBUS);
	pthread_sigmask(SIG_UNBLOCK, &set, &oldset);

	if (sigsetjmp(memset_args->env, 1)) {
	ret = -EFAULT;
	} else {
	char *addr = memset_args->addr;
	size_t numpages = memset_args->numpages;
	size_t hpagesize = memset_args->hpagesize;
	size_t i;
	for (i = 0; i < numpages; i++) {
	/*
	* Read & write back the same value, so we don't
	* corrupt existing user/app data that might be
	* stored.
	*
	* 'volatile' to stop compiler optimizing this away
	* to a no-op
	*/
	(volatile char )addr = *addr;
	addr += hpagesize;
	}
	}
	pthread_sigmask(SIG_SETMASK, &oldset, NULL);
	return (void *)(uintptr_t)ret;
	}

	static void do_madv_populate_write_pages(void arg)
	{
	MemsetThread memset_args = (MemsetThread )arg;
	const size_t size = memset_args->numpages * memset_args->hpagesize;
	char * const addr = memset_args->addr;
	int ret = 0;

	/* See do_touch_pages(). */
	qemu_mutex_lock(&page_mutex);
	while (!memset_args->context->all_threads_created) {
	qemu_cond_wait(&page_cond, &page_mutex);
	}
	qemu_mutex_unlock(&page_mutex);

	if (size && qemu_madvise(addr, size, QEMU_MADV_POPULATE_WRITE)) {
	ret = -errno;
	}
	return (void *)(uintptr_t)ret;
	}

	static inline int get_memset_num_threads(size_t hpagesize, size_t numpages,
	int smp_cpus)
	{
	long host_procs = sysconf(_SC_NPROCESSORS_ONLN);
	int ret = 1;

	if (host_procs > 0) {
	ret = MIN(MIN(host_procs, MAX_MEM_PREALLOC_THREAD_COUNT), smp_cpus);
	}

	/* Especially with gigantic pages, don't create more threads than pages. */
	ret = MIN(ret, numpages);
	/* Don't start threads to prealloc comparatively little memory. */
	ret = MIN(ret, MAX(1, hpagesize * numpages / (64 * MiB)));

	/* In case sysconf() fails, we fall back to single threaded */
	return ret;
	}

	static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
	int smp_cpus, bool use_madv_populate_write)
	{
	static gsize initialized = 0;
	MemsetContext context = {
	.num_threads = get_memset_num_threads(hpagesize, numpages, smp_cpus),
	};
	size_t numpages_per_thread, leftover;
	void (touch_fn)(void *);
	int ret = 0, i = 0;
	char *addr = area;

	if (g_once_init_enter(&initialized)) {
	qemu_mutex_init(&page_mutex);
	qemu_cond_init(&page_cond);
	g_once_init_leave(&initialized, 1);
	}

	if (use_madv_populate_write) {
	/* Avoid creating a single thread for MADV_POPULATE_WRITE */
	if (context.num_threads == 1) {
	if (qemu_madvise(area, hpagesize * numpages,
	QEMU_MADV_POPULATE_WRITE)) {
	return -errno;
	}
	return 0;
	}
	touch_fn = do_madv_populate_write_pages;
	} else {
	touch_fn = do_touch_pages;
	}

	context.threads = g_new0(MemsetThread, context.num_threads);
	numpages_per_thread = numpages / context.num_threads;
	leftover = numpages % context.num_threads;
	for (i = 0; i < context.num_threads; i++) {
	context.threads[i].addr = addr;
	context.threads[i].numpages = numpages_per_thread + (i < leftover);
	context.threads[i].hpagesize = hpagesize;
	context.threads[i].context = &context;
	qemu_thread_create(&context.threads[i].pgthread, "touch_pages",
	touch_fn, &context.threads[i],
	QEMU_THREAD_JOINABLE);
	addr += context.threads[i].numpages * hpagesize;
	}

	if (!use_madv_populate_write) {
	sigbus_memset_context = &context;
	}

	qemu_mutex_lock(&page_mutex);
	context.all_threads_created = true;
	qemu_cond_broadcast(&page_cond);
	qemu_mutex_unlock(&page_mutex);

	for (i = 0; i < context.num_threads; i++) {
	int tmp = (uintptr_t)qemu_thread_join(&context.threads[i].pgthread);

	if (tmp) {
	ret = tmp;
	}
	}

	if (!use_madv_populate_write) {
	sigbus_memset_context = NULL;
	}
	g_free(context.threads);

	return ret;
	}

	static bool madv_populate_write_possible(char *area, size_t pagesize)
	{
	return !qemu_madvise(area, pagesize, QEMU_MADV_POPULATE_WRITE) \|\|
	errno != EINVAL;
	}

	void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
	Error **errp)
	{
	static gsize initialized;
	int ret;
	size_t hpagesize = qemu_fd_getpagesize(fd);
	size_t numpages = DIV_ROUND_UP(memory, hpagesize);
	bool use_madv_populate_write;
	struct sigaction act;

	/*
	* Sense on every invocation, as MADV_POPULATE_WRITE cannot be used for
	* some special mappings, such as mapping /dev/mem.
	*/
	use_madv_populate_write = madv_populate_write_possible(area, hpagesize);

	if (!use_madv_populate_write) {
	if (g_once_init_enter(&initialized)) {
	qemu_mutex_init(&sigbus_mutex);
	g_once_init_leave(&initialized, 1);
	}

	qemu_mutex_lock(&sigbus_mutex);
	memset(&act, 0, sizeof(act));
	#ifdef CONFIG_LINUX
	act.sa_sigaction = &sigbus_handler;
	act.sa_flags = SA_SIGINFO;
	#else /* CONFIG_LINUX */
	act.sa_handler = &sigbus_handler;
	act.sa_flags = 0;
	#endif /* CONFIG_LINUX */

	ret = sigaction(SIGBUS, &act, &sigbus_oldact);
	if (ret) {
	qemu_mutex_unlock(&sigbus_mutex);
	error_setg_errno(errp, errno,
	"os_mem_prealloc: failed to install signal handler");
	return;
	}
	}

	/* touch pages simultaneously */
	ret = touch_all_pages(area, hpagesize, numpages, smp_cpus,
	use_madv_populate_write);
	if (ret) {
	error_setg_errno(errp, -ret,
	"os_mem_prealloc: preallocating memory failed");
	}

	if (!use_madv_populate_write) {
	ret = sigaction(SIGBUS, &sigbus_oldact, NULL);
	if (ret) {
	/* Terminate QEMU since it can't recover from error */
	perror("os_mem_prealloc: failed to reinstall signal handler");
	exit(1);
	}
	qemu_mutex_unlock(&sigbus_mutex);
	}
	}

	char *qemu_get_pid_name(pid_t pid)
	{
	char *name = NULL;

	#if defined(__FreeBSD__)
	/* BSDs don't have /proc, but they provide a nice substitute */
	struct kinfo_proc *proc = kinfo_getproc(pid);

	if (proc) {
	name = g_strdup(proc->ki_comm);
	free(proc);
	}
	#else
	/* Assume a system with reasonable procfs */
	char *pid_path;
	size_t len;

	pid_path = g_strdup_printf("/proc/%d/cmdline", pid);
	g_file_get_contents(pid_path, &name, &len, NULL);
	g_free(pid_path);
	#endif

	return name;
	}


	pid_t qemu_fork(Error **errp)
	{
	sigset_t oldmask, newmask;
	struct sigaction sig_action;
	int saved_errno;
	pid_t pid;

	/*
	* Need to block signals now, so that child process can safely
	* kill off caller's signal handlers without a race.
	*/
	sigfillset(&newmask);
	if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) {
	error_setg_errno(errp, errno,
	"cannot block signals");
	return -1;
	}

	pid = fork();
	saved_errno = errno;

	if (pid < 0) {
	/* attempt to restore signal mask, but ignore failure, to
	* avoid obscuring the fork failure */
	(void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	error_setg_errno(errp, saved_errno,
	"cannot fork child process");
	errno = saved_errno;
	return -1;
	} else if (pid) {
	/* parent process */

	/* Restore our original signal mask now that the child is
	* safely running. Only documented failures are EFAULT (not
	* possible, since we are using just-grabbed mask) or EINVAL
	* (not possible, since we are using correct arguments). */
	(void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
	} else {
	/* child process */
	size_t i;

	/* Clear out all signal handlers from parent so nothing
	* unexpected can happen in our child once we unblock
	* signals */
	sig_action.sa_handler = SIG_DFL;
	sig_action.sa_flags = 0;
	sigemptyset(&sig_action.sa_mask);

	for (i = 1; i < NSIG; i++) {
	/* Only possible errors are EFAULT or EINVAL The former
	* won't happen, the latter we expect, so no need to check
	* return value */
	(void)sigaction(i, &sig_action, NULL);
	}

	/* Unmask all signals in child, since we've no idea what the
	* caller's done with their signal mask and don't want to
	* propagate that to children */
	sigemptyset(&newmask);
	if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) {
	Error *local_err = NULL;
	error_setg_errno(&local_err, errno,
	"cannot unblock signals");
	error_report_err(local_err);
	_exit(1);
	}
	}
	return pid;
	}

	void qemu_alloc_stack(size_t sz)
	{
	void ptr, guardpage;
	int flags;
	#ifdef CONFIG_DEBUG_STACK_USAGE
	void *ptr2;
	#endif
	size_t pagesz = qemu_real_host_page_size();
	#ifdef _SC_THREAD_STACK_MIN
	/* avoid stacks smaller than _SC_THREAD_STACK_MIN */
	long min_stack_sz = sysconf(_SC_THREAD_STACK_MIN);
	sz = MAX(MAX(min_stack_sz, 0), sz);
	#endif
	/* adjust stack size to a multiple of the page size */
	sz = ROUND_UP(sz, pagesz);
	/* allocate one extra page for the guard page */
	*sz += pagesz;

	flags = MAP_PRIVATE \| MAP_ANONYMOUS;
	#if defined(MAP_STACK) && defined(__OpenBSD__)
	/* Only enable MAP_STACK on OpenBSD. Other OS's such as
	* Linux/FreeBSD/NetBSD have a flag with the same name
	* but have differing functionality. OpenBSD will SEGV
	* if it spots execution with a stack pointer pointing
	* at memory that was not allocated with MAP_STACK.
	*/
	flags \|= MAP_STACK;
	#endif

	ptr = mmap(NULL, *sz, PROT_READ \| PROT_WRITE, flags, -1, 0);
	if (ptr == MAP_FAILED) {
	perror("failed to allocate memory for stack");
	abort();
	}

	#if defined(HOST_IA64)
	/* separate register stack */
	guardpage = ptr + (((*sz - pagesz) / 2) & ~pagesz);
	#elif defined(HOST_HPPA)
	/* stack grows up */
	guardpage = ptr + *sz - pagesz;
	#else
	/* stack grows down */
	guardpage = ptr;
	#endif
	if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
	perror("failed to set up stack guard page");
	abort();
	}

	#ifdef CONFIG_DEBUG_STACK_USAGE
	for (ptr2 = ptr + pagesz; ptr2 < ptr + *sz; ptr2 += sizeof(uint32_t)) {
	(uint32_t )ptr2 = 0xdeadbeaf;
	}
	#endif

	return ptr;
	}

	#ifdef CONFIG_DEBUG_STACK_USAGE
	static __thread unsigned int max_stack_usage;
	#endif

	void qemu_free_stack(void *stack, size_t sz)
	{
	#ifdef CONFIG_DEBUG_STACK_USAGE
	unsigned int usage;
	void *ptr;

	for (ptr = stack + qemu_real_host_page_size(); ptr < stack + sz;
	ptr += sizeof(uint32_t)) {
	if ((uint32_t )ptr != 0xdeadbeaf) {
	break;
	}
	}
	usage = sz - (uintptr_t) (ptr - stack);
	if (usage > max_stack_usage) {
	error_report("thread %d max stack usage increased from %u to %u",
	qemu_get_thread_id(), max_stack_usage, usage);
	max_stack_usage = usage;
	}
	#endif

	munmap(stack, sz);
	}

	/*
	* Disable CFI checks.
	* We are going to call a signal hander directly. Such handler may or may not
	* have been defined in our binary, so there's no guarantee that the pointer
	* used to set the handler is a cfi-valid pointer. Since the handlers are
	* stored in kernel memory, changing the handler to an attacker-defined
	* function requires being able to call a sigaction() syscall,
	* which is not as easy as overwriting a pointer in memory.
	*/
	QEMU_DISABLE_CFI
	void sigaction_invoke(struct sigaction *action,
	struct qemu_signalfd_siginfo *info)
	{
	siginfo_t si = {};
	si.si_signo = info->ssi_signo;
	si.si_errno = info->ssi_errno;
	si.si_code = info->ssi_code;

	/* Convert the minimal set of fields defined by POSIX.
	* Positive si_code values are reserved for kernel-generated
	* signals, where the valid siginfo fields are determined by
	* the signal number. But according to POSIX, it is unspecified
	* whether SI_USER and SI_QUEUE have values less than or equal to
	* zero.
	*/
	if (info->ssi_code == SI_USER \|\| info->ssi_code == SI_QUEUE \|\|
	info->ssi_code <= 0) {
	/* SIGTERM, etc. */
	si.si_pid = info->ssi_pid;
	si.si_uid = info->ssi_uid;
	} else if (info->ssi_signo == SIGILL \|\| info->ssi_signo == SIGFPE \|\|
	info->ssi_signo == SIGSEGV \|\| info->ssi_signo == SIGBUS) {
	si.si_addr = (void *)(uintptr_t)info->ssi_addr;
	} else if (info->ssi_signo == SIGCHLD) {
	si.si_pid = info->ssi_pid;
	si.si_status = info->ssi_status;
	si.si_uid = info->ssi_uid;
	}
	action->sa_sigaction(info->ssi_signo, &si, NULL);
	}

	size_t qemu_get_host_physmem(void)
	{
	#ifdef _SC_PHYS_PAGES
	long pages = sysconf(_SC_PHYS_PAGES);
	if (pages > 0) {
	if (pages > SIZE_MAX / qemu_real_host_page_size()) {
	return SIZE_MAX;
	} else {
	return pages * qemu_real_host_page_size();
	}
	}
	#endif
	return 0;
	}

	int qemu_msync(void *addr, size_t length, int fd)
	{
	size_t align_mask = ~(qemu_real_host_page_size() - 1);

	/**
	* There are no strict reqs as per the length of mapping
	* to be synced. Still the length needs to follow the address
	* alignment changes. Additionally - round the size to the multiple
	* of PAGE_SIZE
	*/
	length += ((uintptr_t)addr & (qemu_real_host_page_size() - 1));
	length = (length + ~align_mask) & align_mask;

	addr = (void *)((uintptr_t)addr & align_mask);

	return msync(addr, length, MS_SYNC);
	}