1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
/*
* 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;
/*
* Close all open file descriptors.
*/
static void close_all_open_fd(void)
{
struct dirent *de;
int fd, dfd;
DIR *dir;
#ifdef CONFIG_CLOSE_RANGE
int r = close_range(0, ~0U, 0);
if (!r) {
/* Success, no need to try other ways. */
return;
}
#endif
dir = opendir("/proc/self/fd");
if (!dir) {
/* If /proc is not mounted, there is nothing that can be done. */
return;
}
/* Avoid closing the directory. */
dfd = dirfd(dir);
for (de = readdir(dir); de; de = readdir(dir)) {
fd = atoi(de->d_name);
if (fd != dfd) {
close(fd);
}
}
closedir(dir);
}
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.
* Not using close_range for increased compatibility with older kernels.
*/
close_all_open_fd();
/* 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);
}
|
