mirror of https://github.com/proxmox/mirror_qemu
144 lines
3.5 KiB
C
144 lines
3.5 KiB
C
/*
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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 "qemu/osdep.h"
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#include <dirent.h>
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#include <sys/prctl.h>
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#include <sched.h>
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#include "qemu/async-teardown.h"
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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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static pid_t the_ppid;
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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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#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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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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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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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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/* At this point the parent process has terminated completely. */
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_exit(0);
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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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/* 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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* 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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/* 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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/* 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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* 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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/* 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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* 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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/* 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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stack_ptr += stack_size;
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return stack_ptr;
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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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the_ppid = getpid();
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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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