| 1 | /* |
| 2 | * Asynchronous teardown |
| 3 | * |
| 4 | * Copyright IBM, Corp. 2022 |
| 5 | * |
| 6 | * Authors: |
| 7 | * Claudio Imbrenda <imbrenda@linux.ibm.com> |
| 8 | * |
| 9 | * This work is licensed under the terms of the GNU GPL, version 2 or (at your |
| 10 | * option) any later version. See the COPYING file in the top-level directory. |
| 11 | * |
| 12 | */ |
| 13 | |
| 14 | #include "qemu/osdep.h" |
| 15 | #include <dirent.h> |
| 16 | #include <sys/prctl.h> |
| 17 | #include <sched.h> |
| 18 | |
| 19 | #include "qemu/async-teardown.h" |
| 20 | |
| 21 | #ifdef _SC_THREAD_STACK_MIN |
| 22 | #define CLONE_STACK_SIZE sysconf(_SC_THREAD_STACK_MIN) |
| 23 | #else |
| 24 | #define CLONE_STACK_SIZE 16384 |
| 25 | #endif |
| 26 | |
| 27 | static pid_t the_ppid; |
| 28 | |
| 29 | static void hup_handler(int signal) |
| 30 | { |
| 31 | /* Check every second if this process has been reparented. */ |
| 32 | while (the_ppid == getppid()) { |
| 33 | /* sleep() is safe to use in a signal handler. */ |
| 34 | sleep(1); |
| 35 | } |
| 36 | |
| 37 | /* At this point the parent process has terminated completely. */ |
| 38 | _exit(0); |
| 39 | } |
| 40 | |
| 41 | static int async_teardown_fn(void *arg) |
| 42 | { |
| 43 | struct sigaction sa = { .sa_handler = hup_handler }; |
| 44 | sigset_t hup_signal; |
| 45 | char name[16]; |
| 46 | |
| 47 | /* Set a meaningful name for this process. */ |
| 48 | snprintf(name, 16, "cleanup/%d", the_ppid); |
| 49 | prctl(PR_SET_NAME, (unsigned long)name); |
| 50 | |
| 51 | /* |
| 52 | * Close all file descriptors that might have been inherited from the |
| 53 | * main qemu process when doing clone, needed to make libvirt happy. |
| 54 | */ |
| 55 | qemu_close_all_open_fd(NULL, 0); |
| 56 | |
| 57 | /* Set up a handler for SIGHUP and unblock SIGHUP. */ |
| 58 | sigaction(SIGHUP, &sa, NULL); |
| 59 | sigemptyset(&hup_signal); |
| 60 | sigaddset(&hup_signal, SIGHUP); |
| 61 | sigprocmask(SIG_UNBLOCK, &hup_signal, NULL); |
| 62 | |
| 63 | /* Ask to receive SIGHUP when the parent dies. */ |
| 64 | prctl(PR_SET_PDEATHSIG, SIGHUP); |
| 65 | |
| 66 | /* |
| 67 | * Sleep forever, unless the parent process has already terminated. The |
| 68 | * only interruption can come from the SIGHUP signal, which in normal |
| 69 | * operation is received when the parent process dies. |
| 70 | */ |
| 71 | if (the_ppid == getppid()) { |
| 72 | pause(); |
| 73 | } |
| 74 | |
| 75 | /* At this point the parent process has terminated completely. */ |
| 76 | _exit(0); |
| 77 | } |
| 78 | |
| 79 | /* |
| 80 | * Allocate a new stack of a reasonable size, and return a pointer to its top. |
| 81 | */ |
| 82 | static void *new_stack_for_clone(void) |
| 83 | { |
| 84 | size_t stack_size = CLONE_STACK_SIZE; |
| 85 | char *stack_ptr; |
| 86 | |
| 87 | /* Allocate a new stack and get a pointer to its top. */ |
| 88 | stack_ptr = qemu_alloc_stack(&stack_size); |
| 89 | stack_ptr += stack_size; |
| 90 | |
| 91 | return stack_ptr; |
| 92 | } |
| 93 | |
| 94 | /* |
| 95 | * Block all signals, start (clone) a new process sharing the address space |
| 96 | * with qemu (CLONE_VM), then restore signals. |
| 97 | */ |
| 98 | void init_async_teardown(void) |
| 99 | { |
| 100 | sigset_t all_signals, old_signals; |
| 101 | |
| 102 | the_ppid = getpid(); |
| 103 | |
| 104 | sigfillset(&all_signals); |
| 105 | sigprocmask(SIG_BLOCK, &all_signals, &old_signals); |
| 106 | clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL); |
| 107 | sigprocmask(SIG_SETMASK, &old_signals, NULL); |
| 108 | } |