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
6 * it under the terms of the GNU General Public License, version 2 only,
7 * as published by the Free Software Foundation.
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.
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.
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");
108 ret
= fchmod(wait_shm_fd
, mode
);
114 #warning "FreeBSD does not support setting file mode on shm FD. Remember that for secure use, lttng-sessiond should be started before applications linked on lttng-ust."
117 DBG("Got the wait shm fd %d", wait_shm_fd
);
122 DBG("Failing to get the wait shm fd");
128 * Return the wait shm mmap for UST application notification. The global
129 * variable is used to indicate if the the session daemon is global
130 * (root:tracing) or running with an unprivileged user.
132 * This returned value is used by futex_wait_update() in futex.c to WAKE all
133 * waiters which are UST application waiting for a session daemon.
135 char *shm_ust_get_mmap(char *shm_path
, int global
)
137 size_t mmap_size
= sysconf(_SC_PAGE_SIZE
);
138 int wait_shm_fd
, ret
;
141 wait_shm_fd
= get_wait_shm(shm_path
, mmap_size
, global
);
142 if (wait_shm_fd
< 0) {
146 wait_shm_mmap
= mmap(NULL
, mmap_size
, PROT_WRITE
| PROT_READ
,
147 MAP_SHARED
, wait_shm_fd
, 0);
149 /* close shm fd immediately after taking the mmap reference */
150 ret
= close(wait_shm_fd
);
152 PERROR("Error closing fd");
155 if (wait_shm_mmap
== MAP_FAILED
) {
156 DBG("mmap error (can be caused by race with ust).");
160 return wait_shm_mmap
;
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