| 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 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. |
| 8 | * |
| 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 |
| 12 | * more details. |
| 13 | * |
| 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. |
| 17 | */ |
| 18 | |
| 19 | #define _GNU_SOURCE |
| 20 | #include <fcntl.h> |
| 21 | #include <limits.h> |
| 22 | #include <sys/mman.h> |
| 23 | #include <sys/stat.h> |
| 24 | #include <sys/types.h> |
| 25 | #include <sys/wait.h> |
| 26 | #include <unistd.h> |
| 27 | #include <urcu.h> |
| 28 | |
| 29 | #include <lttngerr.h> |
| 30 | |
| 31 | #include "benchmark.h" |
| 32 | #include "measures.h" |
| 33 | #include "shm.h" |
| 34 | |
| 35 | /* |
| 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 |
| 41 | * starts. |
| 42 | */ |
| 43 | static int get_wait_shm(char *shm_path, size_t mmap_size, int global) |
| 44 | { |
| 45 | int wait_shm_fd, ret; |
| 46 | mode_t mode; |
| 47 | |
| 48 | tracepoint(ust_notify_perms_start); |
| 49 | |
| 50 | /* Default permissions */ |
| 51 | mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP; |
| 52 | |
| 53 | /* Change owner of the shm path */ |
| 54 | if (global) { |
| 55 | ret = chown(shm_path, 0, 0); |
| 56 | if (ret < 0) { |
| 57 | if (errno != ENOENT) { |
| 58 | perror("chown wait shm"); |
| 59 | goto error; |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | /* |
| 64 | * If global session daemon, any application can register so the shm |
| 65 | * needs to be set in read-only mode for others. |
| 66 | */ |
| 67 | mode |= S_IROTH; |
| 68 | } else { |
| 69 | ret = chown(shm_path, getuid(), getgid()); |
| 70 | if (ret < 0) { |
| 71 | if (errno != ENOENT) { |
| 72 | perror("chown wait shm"); |
| 73 | goto error; |
| 74 | } |
| 75 | } |
| 76 | } |
| 77 | |
| 78 | /* |
| 79 | * Set permissions to the shm even if we did not create the shm. |
| 80 | */ |
| 81 | ret = chmod(shm_path, mode); |
| 82 | if (ret < 0) { |
| 83 | if (errno != ENOENT) { |
| 84 | perror("chmod wait shm"); |
| 85 | goto error; |
| 86 | } |
| 87 | } |
| 88 | |
| 89 | /* |
| 90 | * We're alone in a child process, so we can modify the process-wide |
| 91 | * umask. |
| 92 | */ |
| 93 | umask(~mode); |
| 94 | |
| 95 | tracepoint(ust_notify_perms_stop); |
| 96 | |
| 97 | tracepoint(ust_notify_shm_start); |
| 98 | /* |
| 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. |
| 101 | */ |
| 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"); |
| 105 | goto error; |
| 106 | } |
| 107 | |
| 108 | ret = ftruncate(wait_shm_fd, mmap_size); |
| 109 | if (ret < 0) { |
| 110 | perror("ftruncate wait shm"); |
| 111 | exit(EXIT_FAILURE); |
| 112 | } |
| 113 | |
| 114 | ret = fchmod(wait_shm_fd, mode); |
| 115 | if (ret < 0) { |
| 116 | perror("fchmod"); |
| 117 | exit(EXIT_FAILURE); |
| 118 | } |
| 119 | |
| 120 | tracepoint(ust_notify_shm_stop); |
| 121 | |
| 122 | DBG("Got the wait shm fd %d", wait_shm_fd); |
| 123 | |
| 124 | return wait_shm_fd; |
| 125 | |
| 126 | error: |
| 127 | DBG("Failing to get the wait shm fd"); |
| 128 | |
| 129 | return -1; |
| 130 | } |
| 131 | |
| 132 | /* |
| 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. |
| 136 | * |
| 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. |
| 139 | */ |
| 140 | char *shm_ust_get_mmap(char *shm_path, int global) |
| 141 | { |
| 142 | size_t mmap_size = sysconf(_SC_PAGE_SIZE); |
| 143 | int wait_shm_fd, ret; |
| 144 | char *wait_shm_mmap; |
| 145 | |
| 146 | wait_shm_fd = get_wait_shm(shm_path, mmap_size, global); |
| 147 | if (wait_shm_fd < 0) { |
| 148 | goto error; |
| 149 | } |
| 150 | |
| 151 | tracepoint(ust_notify_mmap_start); |
| 152 | |
| 153 | wait_shm_mmap = mmap(NULL, mmap_size, PROT_WRITE | PROT_READ, |
| 154 | MAP_SHARED, wait_shm_fd, 0); |
| 155 | |
| 156 | tracepoint(ust_notify_mmap_stop); |
| 157 | /* close shm fd immediately after taking the mmap reference */ |
| 158 | ret = close(wait_shm_fd); |
| 159 | if (ret) { |
| 160 | perror("Error closing fd"); |
| 161 | } |
| 162 | |
| 163 | if (wait_shm_mmap == MAP_FAILED) { |
| 164 | DBG("mmap error (can be caused by race with ust)."); |
| 165 | goto error; |
| 166 | } |
| 167 | |
| 168 | return wait_shm_mmap; |
| 169 | |
| 170 | error: |
| 171 | return NULL; |
| 172 | } |