Fix: disable all ust events
[lttng-tools.git] / src / bin / lttng-sessiond / shm.c
1 /*
2 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License, version 2 only,
7 * as published by the Free Software Foundation.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
17 */
18
19 #define _GNU_SOURCE
20 #define _LGPL_SOURCE
21 #include <fcntl.h>
22 #include <limits.h>
23 #include <sys/mman.h>
24 #include <sys/stat.h>
25 #include <sys/types.h>
26 #include <sys/wait.h>
27 #include <unistd.h>
28 #include <urcu.h>
29
30 #include <common/error.h>
31
32 #include "shm.h"
33
34 /*
35 * Using fork to set umask in the child process (not multi-thread safe). We
36 * deal with the shm_open vs ftruncate race (happening when the sessiond owns
37 * the shm and does not let everybody modify it, to ensure safety against
38 * shm_unlink) by simply letting the mmap fail and retrying after a few
39 * seconds. For global shm, everybody has rw access to it until the sessiond
40 * starts.
41 */
42 static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
43 {
44 int wait_shm_fd, ret;
45 mode_t mode;
46
47 assert(shm_path);
48
49 /* Default permissions */
50 mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
51
52 /*
53 * Change owner of the shm path.
54 */
55 if (global) {
56 /*
57 * If global session daemon, any application can
58 * register. Make it initially writeable so applications
59 * registering concurrently can do ftruncate() by
60 * themselves.
61 */
62 mode |= S_IROTH | S_IWOTH;
63 }
64
65 /*
66 * We're alone in a child process, so we can modify the process-wide
67 * umask.
68 */
69 umask(~mode);
70
71 /*
72 * Try creating shm (or get rw access). We don't do an exclusive open,
73 * because we allow other processes to create+ftruncate it concurrently.
74 */
75 wait_shm_fd = shm_open(shm_path, O_RDWR | O_CREAT, mode);
76 if (wait_shm_fd < 0) {
77 PERROR("shm_open wait shm");
78 goto error;
79 }
80
81 ret = ftruncate(wait_shm_fd, mmap_size);
82 if (ret < 0) {
83 PERROR("ftruncate wait shm");
84 exit(EXIT_FAILURE);
85 }
86
87 #ifndef __FreeBSD__
88 if (global) {
89 ret = fchown(wait_shm_fd, 0, 0);
90 if (ret < 0) {
91 PERROR("fchown");
92 exit(EXIT_FAILURE);
93 }
94 /*
95 * If global session daemon, any application can
96 * register so the shm needs to be set in read-only mode
97 * for others.
98 */
99 mode &= ~S_IWOTH;
100 ret = fchmod(wait_shm_fd, mode);
101 if (ret < 0) {
102 PERROR("fchmod");
103 exit(EXIT_FAILURE);
104 }
105 } else {
106 ret = fchown(wait_shm_fd, getuid(), getgid());
107 if (ret < 0) {
108 PERROR("fchown");
109 exit(EXIT_FAILURE);
110 }
111 }
112 #else
113 #warning "FreeBSD does not support setting file mode on shm FD."
114 #endif
115
116 DBG("Got the wait shm fd %d", wait_shm_fd);
117
118 return wait_shm_fd;
119
120 error:
121 DBG("Failing to get the wait shm fd");
122
123 return -1;
124 }
125
126 /*
127 * Return the wait shm mmap for UST application notification. The global
128 * variable is used to indicate if the the session daemon is global
129 * (root:tracing) or running with an unprivileged user.
130 *
131 * This returned value is used by futex_wait_update() in futex.c to WAKE all
132 * waiters which are UST application waiting for a session daemon.
133 */
134 char *shm_ust_get_mmap(char *shm_path, int global)
135 {
136 size_t mmap_size;
137 int wait_shm_fd, ret;
138 char *wait_shm_mmap;
139 long sys_page_size;
140
141 assert(shm_path);
142
143 sys_page_size = sysconf(_SC_PAGE_SIZE);
144 if (sys_page_size < 0) {
145 PERROR("sysconf PAGE_SIZE");
146 goto error;
147 }
148 mmap_size = sys_page_size;
149
150 wait_shm_fd = get_wait_shm(shm_path, mmap_size, global);
151 if (wait_shm_fd < 0) {
152 goto error;
153 }
154
155 wait_shm_mmap = mmap(NULL, mmap_size, PROT_WRITE | PROT_READ,
156 MAP_SHARED, wait_shm_fd, 0);
157
158 /* close shm fd immediately after taking the mmap reference */
159 ret = close(wait_shm_fd);
160 if (ret) {
161 PERROR("Error closing fd");
162 }
163
164 if (wait_shm_mmap == MAP_FAILED) {
165 DBG("mmap error (can be caused by race with ust).");
166 goto error;
167 }
168
169 return wait_shm_mmap;
170
171 error:
172 return NULL;
173 }
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