2 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License as published by the Free
7 * Software Foundation; only version 2 of the License.
9 * This program is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
14 * You should have received a copy of the GNU General Public License along with
15 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
16 * Place - Suite 330, Boston, MA 02111-1307, USA.
24 #include <sys/types.h>
31 #include "benchmark.h"
36 * Using fork to set umask in the child process (not multi-thread safe). We
37 * deal with the shm_open vs ftruncate race (happening when the sessiond owns
38 * the shm and does not let everybody modify it, to ensure safety against
39 * shm_unlink) by simply letting the mmap fail and retrying after a few
40 * seconds. For global shm, everybody has rw access to it until the sessiond
43 static int get_wait_shm(char *shm_path
, size_t mmap_size
, int global
)
48 tracepoint(ust_notify_perms_start
);
50 /* Default permissions */
51 mode
= S_IRUSR
| S_IWUSR
| S_IRGRP
| S_IWGRP
;
53 /* Change owner of the shm path */
55 ret
= chown(shm_path
, 0, 0);
57 if (errno
!= ENOENT
) {
58 perror("chown wait shm");
64 * If global session daemon, any application can register so the shm
65 * needs to be set in read-only mode for others.
69 ret
= chown(shm_path
, getuid(), getgid());
71 if (errno
!= ENOENT
) {
72 perror("chown wait shm");
79 * Set permissions to the shm even if we did not create the shm.
81 ret
= chmod(shm_path
, mode
);
83 if (errno
!= ENOENT
) {
84 perror("chmod wait shm");
90 * We're alone in a child process, so we can modify the process-wide
95 tracepoint(ust_notify_perms_stop
);
97 tracepoint(ust_notify_shm_start
);
99 * Try creating shm (or get rw access). We don't do an exclusive open,
100 * because we allow other processes to create+ftruncate it concurrently.
102 wait_shm_fd
= shm_open(shm_path
, O_RDWR
| O_CREAT
, mode
);
103 if (wait_shm_fd
< 0) {
104 perror("shm_open wait shm");
108 ret
= ftruncate(wait_shm_fd
, mmap_size
);
110 perror("ftruncate wait shm");
114 ret
= fchmod(wait_shm_fd
, mode
);
120 tracepoint(ust_notify_shm_stop
);
122 DBG("Got the wait shm fd %d", wait_shm_fd
);
127 DBG("Failing to get the wait shm fd");
133 * Return the wait shm mmap for UST application notification. The global
134 * variable is used to indicate if the the session daemon is global
135 * (root:tracing) or running with an unprivileged user.
137 * This returned value is used by futex_wait_update() in futex.c to WAKE all
138 * waiters which are UST application waiting for a session daemon.
140 char *shm_ust_get_mmap(char *shm_path
, int global
)
142 size_t mmap_size
= sysconf(_SC_PAGE_SIZE
);
143 int wait_shm_fd
, ret
;
146 wait_shm_fd
= get_wait_shm(shm_path
, mmap_size
, global
);
147 if (wait_shm_fd
< 0) {
151 tracepoint(ust_notify_mmap_start
);
153 wait_shm_mmap
= mmap(NULL
, mmap_size
, PROT_WRITE
| PROT_READ
,
154 MAP_SHARED
, wait_shm_fd
, 0);
156 tracepoint(ust_notify_mmap_stop
);
157 /* close shm fd immediately after taking the mmap reference */
158 ret
= close(wait_shm_fd
);
160 perror("Error closing fd");
163 if (wait_shm_mmap
== MAP_FAILED
) {
164 DBG("mmap error (can be caused by race with ust).");
168 return wait_shm_mmap
;
This page took 0.045053 seconds and 4 git commands to generate.