| 1 | /* |
| 2 | * buildrun.c: wait to run one command until an instance of another |
| 3 | * completes successfully |
| 4 | */ |
| 5 | |
| 6 | #include <stdio.h> |
| 7 | #include <string.h> |
| 8 | #include <stdlib.h> |
| 9 | #include <errno.h> |
| 10 | |
| 11 | #include <sys/types.h> |
| 12 | #include <sys/wait.h> |
| 13 | #include <sys/stat.h> |
| 14 | #include <fcntl.h> |
| 15 | #include <unistd.h> |
| 16 | |
| 17 | /* |
| 18 | * Implementation strategy |
| 19 | * ----------------------- |
| 20 | * |
| 21 | * The basic plan for making buildrun -r wait for buildrun -w is that |
| 22 | * buildrun -w creates a named pipe, opens it for writing, and does |
| 23 | * not actually write to it; then buildrun -r opens the same named |
| 24 | * pipe for reading. When buildrun -w terminates, anything which was |
| 25 | * trying to read from the pipe receives EOF, so buildrun -r can wake |
| 26 | * up and look to see if the run was successful. |
| 27 | * |
| 28 | * buildrun -w's report of success or failure is done by the very |
| 29 | * simple approach of deleting the pipe file before terminating, if |
| 30 | * the run was successful. So after buildrun -r receives EOF on the |
| 31 | * pipe, it immediately tries to open it again - and if it gets |
| 32 | * ENOENT, that's the success condition. Otherwise it reopens the pipe |
| 33 | * and blocks again until another buildrun -w succeeds. |
| 34 | * |
| 35 | * If the run was unsuccessful, buildrun -r must block immediately and |
| 36 | * stay blocked until buildrun -w next runs. This is achieved |
| 37 | * automatically by the above strategy, since attempting to open a |
| 38 | * pipe for reading when nothing is trying to write it will cause the |
| 39 | * open(2) call to block until something opens the pipe for writing. |
| 40 | * |
| 41 | * Likewise, if the last buildrun -w was unsuccessful and no -w run is |
| 42 | * active at the moment buildrun -r starts in the first place, |
| 43 | * buildrun -r must block until one starts up - and again, this is |
| 44 | * done automatically by the attempt to open the pipe for reading. |
| 45 | * |
| 46 | * Of course, the blocking open behaviour of named pipes works both |
| 47 | * ways: if buildrun -w tried to open the pipe for writing when no |
| 48 | * buildrun -r is trying to read it, _it_ would block. For that |
| 49 | * reason, buildrun -w actually opens with O_RDWR, so it can't block. |
| 50 | * |
| 51 | * Just in case the user tries to run two buildrun -w instances on the |
| 52 | * same control file, we also flock(LOCK_EX) the named pipe once we've |
| 53 | * opened it, so that the second -w instance can cleanly report the |
| 54 | * error condition. |
| 55 | * |
| 56 | * Finally, there is a small race condition in the mechanism I've just |
| 57 | * described. Suppose one buildrun -w instance finishes and deletes |
| 58 | * its pipe file - but before buildrun -r manages to unblock and |
| 59 | * notice the file's absence, another buildrun -w starts up and |
| 60 | * recreates it. This is a more or less theoretical risk in the |
| 61 | * interactive environments where I expect this tool to be used, but |
| 62 | * even so, I like to solve these problems where I can; what I do is |
| 63 | * to create not just a named pipe, but a _subdirectory_ containing a |
| 64 | * named pipe. So a successful buildrun -w deletes the pipe and |
| 65 | * removes the containing directory; a subsequent buildrun -w will |
| 66 | * create a fresh directory and pipe. Then buildrun -r starts by |
| 67 | * setting its _cwd_ to the directory containing the pipe - which |
| 68 | * means that if one buildrun -w finishes and another one starts, |
| 69 | * buildrun -r will still have its cwd pointing at the orphaned |
| 70 | * directory from the first, and won't accidentally find the pipe file |
| 71 | * created by the second in its own directory. |
| 72 | */ |
| 73 | |
| 74 | #define PIPEFILE "pipe" |
| 75 | |
| 76 | char *ctldir, *pipepath, **command; |
| 77 | |
| 78 | int writemode(void) |
| 79 | { |
| 80 | pid_t pid; |
| 81 | int fd, status; |
| 82 | |
| 83 | if (mkdir(ctldir, 0700) < 0 && errno != EEXIST) { |
| 84 | fprintf(stderr, "buildrun: %s: mkdir: %s\n", ctldir, strerror(errno)); |
| 85 | return 1; |
| 86 | } |
| 87 | if (mknod(pipepath, S_IFIFO | 0600, 0) < 0 && errno != EEXIST) { |
| 88 | fprintf(stderr, "buildrun: %s: mknod: %s\n", pipepath,strerror(errno)); |
| 89 | return 1; |
| 90 | } |
| 91 | fd = open(pipepath, O_RDWR); |
| 92 | if (fd < 0) { |
| 93 | fprintf(stderr, "buildrun: %s: open: %s\n", pipepath, strerror(errno)); |
| 94 | return 1; |
| 95 | } |
| 96 | if (flock(fd, LOCK_EX | LOCK_NB) < 0) { |
| 97 | if (errno == EAGAIN) { |
| 98 | fprintf(stderr, "buildrun: another write process " |
| 99 | "is already active\n"); |
| 100 | } else { |
| 101 | fprintf(stderr, "buildrun: %s: flock: %s\n", |
| 102 | pipepath, strerror(errno)); |
| 103 | } |
| 104 | return 1; |
| 105 | } |
| 106 | |
| 107 | pid = fork(); |
| 108 | if (pid < 0) { |
| 109 | fprintf(stderr, "buildrun: fork: %s\n", strerror(errno)); |
| 110 | return 1; |
| 111 | } else if (pid == 0) { |
| 112 | close(fd); |
| 113 | execvp(command[0], command); |
| 114 | fprintf(stderr, "buildrun: %s: exec: %s\n", |
| 115 | command[0], strerror(errno)); |
| 116 | return 127; |
| 117 | } |
| 118 | |
| 119 | while (1) { |
| 120 | if (waitpid(pid, &status, 0) < 0) { |
| 121 | fprintf(stderr, "buildrun: wait: %s\n", strerror(errno)); |
| 122 | return 1; |
| 123 | } |
| 124 | if (WIFEXITED(status)) { |
| 125 | status = WEXITSTATUS(status); |
| 126 | break; |
| 127 | } else if (WIFSIGNALED(status)) { |
| 128 | status = 128 | WTERMSIG(status); |
| 129 | break; |
| 130 | } |
| 131 | } |
| 132 | |
| 133 | if (status == 0) { |
| 134 | if (remove(pipepath) < 0) { |
| 135 | fprintf(stderr, "buildrun: %s: remove: %s\n", pipepath, |
| 136 | strerror(errno)); |
| 137 | return 1; |
| 138 | } |
| 139 | if (rmdir(ctldir) < 0) { |
| 140 | fprintf(stderr, "buildrun: %s: rmdir: %s\n", ctldir, |
| 141 | strerror(errno)); |
| 142 | return 1; |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | return status; |
| 147 | } |
| 148 | |
| 149 | int readmode() |
| 150 | { |
| 151 | pid_t pid; |
| 152 | int fd, ret, status; |
| 153 | char buf[1]; |
| 154 | |
| 155 | /* |
| 156 | * Our strategy against race conditions relies on changing our cwd |
| 157 | * to the control dir, but that will confuse the user command if |
| 158 | * we exec one afterwards. So we do most of our work in a |
| 159 | * subprocess, and don't pollute our main process context. |
| 160 | */ |
| 161 | pid = fork(); |
| 162 | if (pid < 0) { |
| 163 | fprintf(stderr, "buildrun: fork: %s\n", strerror(errno)); |
| 164 | return 1; |
| 165 | } else if (pid == 0) { |
| 166 | /* |
| 167 | * The main show. |
| 168 | */ |
| 169 | if (chdir(ctldir) < 0) { |
| 170 | if (errno == ENOENT) { |
| 171 | /* |
| 172 | * If the control directory doesn't exist at all, it |
| 173 | * must be because the last -w run completed |
| 174 | * successfully, so we immediately return success. |
| 175 | */ |
| 176 | return 0; |
| 177 | } |
| 178 | fprintf(stderr, "buildrun: %s: chdir: %s\n", |
| 179 | ctldir, strerror(errno)); |
| 180 | return 1; |
| 181 | } |
| 182 | while (1) { |
| 183 | fd = open(PIPEFILE, O_RDONLY); |
| 184 | if (fd < 0) { |
| 185 | if (errno == ENOENT) |
| 186 | return 0; /* success! */ |
| 187 | |
| 188 | fprintf(stderr, "buildrun: %s: open: %s\n", |
| 189 | pipepath, strerror(errno)); |
| 190 | return 1; |
| 191 | } |
| 192 | |
| 193 | ret = read(fd, buf, 1); |
| 194 | if (ret < 0) { |
| 195 | fprintf(stderr, "buildrun: %s: read: %s\n", |
| 196 | pipepath, strerror(errno)); |
| 197 | return 1; |
| 198 | } else if (ret > 0) { |
| 199 | fprintf(stderr, "buildrun: %s: read: unexpectedly received " |
| 200 | "some data!\n", pipepath, strerror(errno)); |
| 201 | return 1; |
| 202 | } |
| 203 | close(fd); |
| 204 | } |
| 205 | } |
| 206 | |
| 207 | while (1) { |
| 208 | if (waitpid(pid, &status, 0) < 0) { |
| 209 | fprintf(stderr, "buildrun: wait: %s\n", strerror(errno)); |
| 210 | return 1; |
| 211 | } |
| 212 | if (WIFEXITED(status)) { |
| 213 | status = WEXITSTATUS(status); |
| 214 | break; |
| 215 | } else if (WIFSIGNALED(status)) { |
| 216 | status = 128 | WTERMSIG(status); |
| 217 | break; |
| 218 | } |
| 219 | } |
| 220 | |
| 221 | if (status != 0) /* something went wrong in child */ |
| 222 | return status; |
| 223 | |
| 224 | /* |
| 225 | * In -r mode, running a command is optional; in the absence of |
| 226 | * one, we simply return true, so the user can invoke as 'buildrun |
| 227 | * -r file && complex shell command'. |
| 228 | */ |
| 229 | if (!command) |
| 230 | return 0; |
| 231 | |
| 232 | execvp(command[0], command); |
| 233 | fprintf(stderr, "buildrun: %s: exec: %s\n", command[0], strerror(errno)); |
| 234 | return 127; |
| 235 | } |
| 236 | |
| 237 | const char usagemsg[] = |
| 238 | "usage: buildrun -w <control_dir> <command> [<args>...]\n" |
| 239 | " or: buildrun -r <control_dir> [<command> [<args>...]]\n" |
| 240 | "where: -w write mode: run a build command\n" |
| 241 | " -r read mode: wait for a build command to succeed\n" |
| 242 | " <control_dir> directory to use for communication; suggest in /tmp\n" |
| 243 | " also: buildrun --version report version number\n" |
| 244 | " buildrun --help display this help text\n" |
| 245 | " buildrun --licence display the (MIT) licence text\n" |
| 246 | ; |
| 247 | |
| 248 | void usage(void) { |
| 249 | fputs(usagemsg, stdout); |
| 250 | } |
| 251 | |
| 252 | const char licencemsg[] = |
| 253 | "buildrun is copyright 2012 Simon Tatham.\n" |
| 254 | "\n" |
| 255 | "Permission is hereby granted, free of charge, to any person\n" |
| 256 | "obtaining a copy of this software and associated documentation files\n" |
| 257 | "(the \"Software\"), to deal in the Software without restriction,\n" |
| 258 | "including without limitation the rights to use, copy, modify, merge,\n" |
| 259 | "publish, distribute, sublicense, and/or sell copies of the Software,\n" |
| 260 | "and to permit persons to whom the Software is furnished to do so,\n" |
| 261 | "subject to the following conditions:\n" |
| 262 | "\n" |
| 263 | "The above copyright notice and this permission notice shall be\n" |
| 264 | "included in all copies or substantial portions of the Software.\n" |
| 265 | "\n" |
| 266 | "THE SOFTWARE IS PROVIDED \"AS IS\", WITHOUT WARRANTY OF ANY KIND,\n" |
| 267 | "EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF\n" |
| 268 | "MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND\n" |
| 269 | "NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS\n" |
| 270 | "BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN\n" |
| 271 | "ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN\n" |
| 272 | "CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE\n" |
| 273 | "SOFTWARE.\n" |
| 274 | ; |
| 275 | |
| 276 | void licence(void) { |
| 277 | fputs(licencemsg, stdout); |
| 278 | } |
| 279 | |
| 280 | void version(void) { |
| 281 | #define SVN_REV "$Revision$" |
| 282 | char rev[sizeof(SVN_REV)]; |
| 283 | char *p, *q; |
| 284 | |
| 285 | strcpy(rev, SVN_REV); |
| 286 | |
| 287 | for (p = rev; *p && *p != ':'; p++); |
| 288 | if (*p) { |
| 289 | p++; |
| 290 | while (*p && isspace(*p)) p++; |
| 291 | for (q = p; *q && *q != '$'; q++); |
| 292 | if (*q) *q = '\0'; |
| 293 | printf("buildrun revision %s\n", p); |
| 294 | } else { |
| 295 | printf("buildrun: unknown version\n"); |
| 296 | } |
| 297 | } |
| 298 | |
| 299 | int main(int argc, char **argv) |
| 300 | { |
| 301 | enum { UNSPEC, READ, WRITE } mode = UNSPEC; |
| 302 | int doing_opts = 1; |
| 303 | |
| 304 | ctldir = NULL; |
| 305 | command = NULL; |
| 306 | |
| 307 | while (--argc > 0) { |
| 308 | char *p = *++argv; |
| 309 | if (doing_opts && *p == '-') { |
| 310 | if (!strcmp(p, "-w")) { |
| 311 | mode = WRITE; |
| 312 | } else if (!strcmp(p, "-r")) { |
| 313 | mode = READ; |
| 314 | } else if (!strcmp(p, "--")) { |
| 315 | doing_opts = 0; |
| 316 | } else if (!strcmp(p, "--version")) { |
| 317 | version(); |
| 318 | return 0; |
| 319 | } else if (!strcmp(p, "--help")) { |
| 320 | usage(); |
| 321 | return 0; |
| 322 | } else if (!strcmp(p, "--licence") || !strcmp(p, "--license")) { |
| 323 | licence(); |
| 324 | return 0; |
| 325 | } else { |
| 326 | fprintf(stderr, "buildrun: unrecognised option '%s'\n", p); |
| 327 | return 1; |
| 328 | } |
| 329 | } else { |
| 330 | if (!ctldir) { |
| 331 | ctldir = p; |
| 332 | } else { |
| 333 | command = argv; |
| 334 | break; |
| 335 | } |
| 336 | } |
| 337 | } |
| 338 | |
| 339 | if (mode == UNSPEC) { |
| 340 | fprintf(stderr, "buildrun: expected -w or -r\n"); |
| 341 | return 1; |
| 342 | } |
| 343 | |
| 344 | if (!ctldir) { |
| 345 | fprintf(stderr, "buildrun: expected a control directory name\n"); |
| 346 | return 1; |
| 347 | } |
| 348 | |
| 349 | pipepath = malloc(strlen(ctldir) + strlen(PIPEFILE) + 2); |
| 350 | if (!pipepath) { |
| 351 | fprintf(stderr, "buildrun: out of memory\n"); |
| 352 | return 1; |
| 353 | } |
| 354 | sprintf(pipepath, "%s/%s", ctldir, PIPEFILE); |
| 355 | |
| 356 | if (mode == WRITE) { |
| 357 | return writemode(); |
| 358 | } else if (mode == READ) { |
| 359 | return readmode(); |
| 360 | } |
| 361 | } |