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>
29 #include <common/error.h>
34 * Using fork to set umask in the child process (not multi-thread safe). We
35 * deal with the shm_open vs ftruncate race (happening when the sessiond owns
36 * the shm and does not let everybody modify it, to ensure safety against
37 * shm_unlink) by simply letting the mmap fail and retrying after a few
38 * seconds. For global shm, everybody has rw access to it until the sessiond
41 static int get_wait_shm(char *shm_path
, size_t mmap_size
, int global
)
46 /* Default permissions */
47 mode
= S_IRUSR
| S_IWUSR
| S_IRGRP
| S_IWGRP
;
49 /* Change owner of the shm path */
51 ret
= chown(shm_path
, 0, 0);
53 if (errno
!= ENOENT
) {
54 perror("chown wait shm");
60 * If global session daemon, any application can register so the shm
61 * needs to be set in read-only mode for others.
65 ret
= chown(shm_path
, getuid(), getgid());
67 if (errno
!= ENOENT
) {
68 perror("chown wait shm");
75 * Set permissions to the shm even if we did not create the shm.
77 ret
= chmod(shm_path
, mode
);
79 if (errno
!= ENOENT
) {
80 perror("chmod wait shm");
86 * We're alone in a child process, so we can modify the process-wide
92 * Try creating shm (or get rw access). We don't do an exclusive open,
93 * because we allow other processes to create+ftruncate it concurrently.
95 wait_shm_fd
= shm_open(shm_path
, O_RDWR
| O_CREAT
, mode
);
96 if (wait_shm_fd
< 0) {
97 perror("shm_open wait shm");
101 ret
= ftruncate(wait_shm_fd
, mmap_size
);
103 perror("ftruncate wait shm");
107 ret
= fchmod(wait_shm_fd
, mode
);
113 DBG("Got the wait shm fd %d", wait_shm_fd
);
118 DBG("Failing to get the wait shm fd");
124 * Return the wait shm mmap for UST application notification. The global
125 * variable is used to indicate if the the session daemon is global
126 * (root:tracing) or running with an unprivileged user.
128 * This returned value is used by futex_wait_update() in futex.c to WAKE all
129 * waiters which are UST application waiting for a session daemon.
131 char *shm_ust_get_mmap(char *shm_path
, int global
)
133 size_t mmap_size
= sysconf(_SC_PAGE_SIZE
);
134 int wait_shm_fd
, ret
;
137 wait_shm_fd
= get_wait_shm(shm_path
, mmap_size
, global
);
138 if (wait_shm_fd
< 0) {
142 wait_shm_mmap
= mmap(NULL
, mmap_size
, PROT_WRITE
| PROT_READ
,
143 MAP_SHARED
, wait_shm_fd
, 0);
145 /* close shm fd immediately after taking the mmap reference */
146 ret
= close(wait_shm_fd
);
148 perror("Error closing fd");
151 if (wait_shm_mmap
== MAP_FAILED
) {
152 DBG("mmap error (can be caused by race with ust).");
156 return wait_shm_mmap
;
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