xref: /openbmc/qemu/util/event_notifier-posix.c (revision 7d87775f)
1 /*
2  * event notifier support
3  *
4  * Copyright Red Hat, Inc. 2010
5  *
6  * Authors:
7  *  Michael S. Tsirkin <mst@redhat.com>
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  */
12 
13 #include "qemu/osdep.h"
14 #include "qemu/cutils.h"
15 #include "qemu/event_notifier.h"
16 #include "qemu/main-loop.h"
17 
18 #ifdef CONFIG_EVENTFD
19 #include <sys/eventfd.h>
20 #endif
21 
22 #ifdef CONFIG_EVENTFD
23 /*
24  * Initialize @e with existing file descriptor @fd.
25  * @fd must be a genuine eventfd object, emulation with pipe won't do.
26  */
27 void event_notifier_init_fd(EventNotifier *e, int fd)
28 {
29     e->rfd = fd;
30     e->wfd = fd;
31     e->initialized = true;
32 }
33 #endif
34 
35 int event_notifier_init(EventNotifier *e, int active)
36 {
37     int fds[2];
38     int ret;
39 
40 #ifdef CONFIG_EVENTFD
41     ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
42 #else
43     ret = -1;
44     errno = ENOSYS;
45 #endif
46     if (ret >= 0) {
47         e->rfd = e->wfd = ret;
48     } else {
49         if (errno != ENOSYS) {
50             return -errno;
51         }
52         if (!g_unix_open_pipe(fds, FD_CLOEXEC, NULL)) {
53             return -errno;
54         }
55         if (!g_unix_set_fd_nonblocking(fds[0], true, NULL)) {
56             ret = -errno;
57             goto fail;
58         }
59         if (!g_unix_set_fd_nonblocking(fds[1], true, NULL)) {
60             ret = -errno;
61             goto fail;
62         }
63         e->rfd = fds[0];
64         e->wfd = fds[1];
65     }
66     e->initialized = true;
67     if (active) {
68         event_notifier_set(e);
69     }
70     return 0;
71 
72 fail:
73     close(fds[0]);
74     close(fds[1]);
75     return ret;
76 }
77 
78 void event_notifier_cleanup(EventNotifier *e)
79 {
80     if (!e->initialized) {
81         return;
82     }
83 
84     if (e->rfd != e->wfd) {
85         close(e->rfd);
86     }
87 
88     e->rfd = -1;
89     close(e->wfd);
90     e->wfd = -1;
91     e->initialized = false;
92 }
93 
94 int event_notifier_get_fd(const EventNotifier *e)
95 {
96     return e->rfd;
97 }
98 
99 int event_notifier_get_wfd(const EventNotifier *e)
100 {
101     return e->wfd;
102 }
103 
104 int event_notifier_set(EventNotifier *e)
105 {
106     static const uint64_t value = 1;
107     ssize_t ret;
108 
109     if (!e->initialized) {
110         return -1;
111     }
112 
113     do {
114         ret = write(e->wfd, &value, sizeof(value));
115     } while (ret < 0 && errno == EINTR);
116 
117     /* EAGAIN is fine, a read must be pending.  */
118     if (ret < 0 && errno != EAGAIN) {
119         return -errno;
120     }
121     return 0;
122 }
123 
124 int event_notifier_test_and_clear(EventNotifier *e)
125 {
126     int value;
127     ssize_t len;
128     char buffer[512];
129 
130     if (!e->initialized) {
131         return 0;
132     }
133 
134     /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
135     value = 0;
136     do {
137         len = read(e->rfd, buffer, sizeof(buffer));
138         value |= (len > 0);
139     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
140 
141     return value;
142 }
143