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@@ -0,0 +1,150 @@
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+/*
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+ * Asynchronous teardown
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+ *
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+ * Copyright IBM, Corp. 2022
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+ *
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+ * Authors:
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+ * Claudio Imbrenda <imbrenda@linux.ibm.com>
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+ *
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+ * This work is licensed under the terms of the GNU GPL, version 2 or (at your
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+ * option) any later version. See the COPYING file in the top-level directory.
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+ *
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+ */
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+#include <stdlib.h>
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+#include <stdio.h>
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+#include <sys/types.h>
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+#include <dirent.h>
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+#include <sys/prctl.h>
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+#include <signal.h>
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+#include <sched.h>
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+#include <unistd.h>
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+
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+#include "qemu/osdep.h"
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+#include "qemu/async-teardown.h"
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+
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+#ifdef _SC_THREAD_STACK_MIN
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+#define CLONE_STACK_SIZE sysconf(_SC_THREAD_STACK_MIN)
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+#else
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+#define CLONE_STACK_SIZE 16384
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+#endif
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+
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+static pid_t the_ppid;
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+
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+/*
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+ * Close all open file descriptors.
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+ */
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+static void close_all_open_fd(void)
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+{
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+ struct dirent *de;
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+ int fd, dfd;
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+ DIR *dir;
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+
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+#ifdef CONFIG_CLOSE_RANGE
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+ int r = close_range(0, ~0U, 0);
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+ if (!r) {
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+ /* Success, no need to try other ways. */
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+ return;
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+ }
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+#endif
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+
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+ dir = opendir("/proc/self/fd");
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+ if (!dir) {
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+ /* If /proc is not mounted, there is nothing that can be done. */
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+ return;
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+ }
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+ /* Avoid closing the directory. */
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+ dfd = dirfd(dir);
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+
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+ for (de = readdir(dir); de; de = readdir(dir)) {
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+ fd = atoi(de->d_name);
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+ if (fd != dfd) {
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+ close(fd);
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+ }
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+ }
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+ closedir(dir);
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+}
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+
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+static void hup_handler(int signal)
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+{
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+ /* Check every second if this process has been reparented. */
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+ while (the_ppid == getppid()) {
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+ /* sleep() is safe to use in a signal handler. */
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+ sleep(1);
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+ }
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+
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+ /* At this point the parent process has terminated completely. */
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+ _exit(0);
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+}
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+
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+static int async_teardown_fn(void *arg)
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+{
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+ struct sigaction sa = { .sa_handler = hup_handler };
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+ sigset_t hup_signal;
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+ char name[16];
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+
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+ /* Set a meaningful name for this process. */
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+ snprintf(name, 16, "cleanup/%d", the_ppid);
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+ prctl(PR_SET_NAME, (unsigned long)name);
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+
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+ /*
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+ * Close all file descriptors that might have been inherited from the
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+ * main qemu process when doing clone, needed to make libvirt happy.
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+ * Not using close_range for increased compatibility with older kernels.
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+ */
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+ close_all_open_fd();
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+
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+ /* Set up a handler for SIGHUP and unblock SIGHUP. */
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+ sigaction(SIGHUP, &sa, NULL);
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+ sigemptyset(&hup_signal);
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+ sigaddset(&hup_signal, SIGHUP);
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+ sigprocmask(SIG_UNBLOCK, &hup_signal, NULL);
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+
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+ /* Ask to receive SIGHUP when the parent dies. */
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+ prctl(PR_SET_PDEATHSIG, SIGHUP);
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+
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+ /*
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+ * Sleep forever, unless the parent process has already terminated. The
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+ * only interruption can come from the SIGHUP signal, which in normal
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+ * operation is received when the parent process dies.
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+ */
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+ if (the_ppid == getppid()) {
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+ pause();
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+ }
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+
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+ /* At this point the parent process has terminated completely. */
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+ _exit(0);
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+}
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+
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+/*
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+ * Allocate a new stack of a reasonable size, and return a pointer to its top.
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+ */
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+static void *new_stack_for_clone(void)
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+{
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+ size_t stack_size = CLONE_STACK_SIZE;
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+ char *stack_ptr;
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+
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+ /* Allocate a new stack and get a pointer to its top. */
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+ stack_ptr = qemu_alloc_stack(&stack_size);
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+#if !defined(HOST_HPPA)
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+ /* The top is at the end of the area, except on HPPA. */
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+ stack_ptr += stack_size;
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+#endif
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+
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+ return stack_ptr;
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+}
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+
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+/*
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+ * Block all signals, start (clone) a new process sharing the address space
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+ * with qemu (CLONE_VM), then restore signals.
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+ */
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+void init_async_teardown(void)
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+{
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+ sigset_t all_signals, old_signals;
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+
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+ the_ppid = getpid();
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+
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+ sigfillset(&all_signals);
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+ sigprocmask(SIG_BLOCK, &all_signals, &old_signals);
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+ clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL);
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+ sigprocmask(SIG_SETMASK, &old_signals, NULL);
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+}
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Claudio Imbrenda