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/*
* Asynchronous teardown
*
* Copyright IBM, Corp. 2022
*
* Authors:
* Claudio Imbrenda <imbrenda@linux.ibm.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or (at your
* option) any later version. See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include <dirent.h>
#include <sys/prctl.h>
#include <sched.h>
#include "qemu/async-teardown.h"
#ifdef _SC_THREAD_STACK_MIN
#define CLONE_STACK_SIZE sysconf(_SC_THREAD_STACK_MIN)
#else
#define CLONE_STACK_SIZE 16384
#endif
static pid_t the_ppid;
static void hup_handler(int signal)
{
/* Check every second if this process has been reparented. */
while (the_ppid == getppid()) {
/* sleep() is safe to use in a signal handler. */
sleep(1);
}
/* At this point the parent process has terminated completely. */
_exit(0);
}
static int async_teardown_fn(void *arg)
{
struct sigaction sa = { .sa_handler = hup_handler };
sigset_t hup_signal;
char name[16];
/* Set a meaningful name for this process. */
snprintf(name, 16, "cleanup/%d", the_ppid);
prctl(PR_SET_NAME, (unsigned long)name);
/*
* Close all file descriptors that might have been inherited from the
* main qemu process when doing clone, needed to make libvirt happy.
*/
qemu_close_all_open_fd(NULL, 0);
/* Set up a handler for SIGHUP and unblock SIGHUP. */
sigaction(SIGHUP, &sa, NULL);
sigemptyset(&hup_signal);
sigaddset(&hup_signal, SIGHUP);
sigprocmask(SIG_UNBLOCK, &hup_signal, NULL);
/* Ask to receive SIGHUP when the parent dies. */
prctl(PR_SET_PDEATHSIG, SIGHUP);
/*
* Sleep forever, unless the parent process has already terminated. The
* only interruption can come from the SIGHUP signal, which in normal
* operation is received when the parent process dies.
*/
if (the_ppid == getppid()) {
pause();
}
/* At this point the parent process has terminated completely. */
_exit(0);
}
/*
* Allocate a new stack of a reasonable size, and return a pointer to its top.
*/
static void *new_stack_for_clone(void)
{
size_t stack_size = CLONE_STACK_SIZE;
char *stack_ptr;
/* Allocate a new stack and get a pointer to its top. */
stack_ptr = qemu_alloc_stack(&stack_size);
stack_ptr += stack_size;
return stack_ptr;
}
/*
* Block all signals, start (clone) a new process sharing the address space
* with qemu (CLONE_VM), then restore signals.
*/
void init_async_teardown(void)
{
sigset_t all_signals, old_signals;
the_ppid = getpid();
sigfillset(&all_signals);
sigprocmask(SIG_BLOCK, &all_signals, &old_signals);
clone(async_teardown_fn, new_stack_for_clone(), CLONE_VM, NULL);
sigprocmask(SIG_SETMASK, &old_signals, NULL);
}
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