| 1 | /* |
| 2 | * Copyright (c) 2005, Junio C Hamano |
| 3 | */ |
| 4 | |
| 5 | #define USE_THE_REPOSITORY_VARIABLE |
| 6 | |
| 7 | #include "git-compat-util.h" |
| 8 | #include "abspath.h" |
| 9 | #include "gettext.h" |
| 10 | #include "lockfile.h" |
| 11 | #include "parse.h" |
| 12 | #include "repository.h" |
| 13 | #include "strbuf.h" |
| 14 | #include "wrapper.h" |
| 15 | |
| 16 | /* |
| 17 | * path = absolute or relative path name |
| 18 | * |
| 19 | * Remove the last path name element from path (leaving the preceding |
| 20 | * "/", if any). If path is empty or the root directory ("/"), set |
| 21 | * path to the empty string. |
| 22 | */ |
| 23 | static void trim_last_path_component(struct strbuf *path) |
| 24 | { |
| 25 | int i = path->len; |
| 26 | |
| 27 | /* back up past trailing slashes, if any */ |
| 28 | while (i && is_dir_sep(path->buf[i - 1])) |
| 29 | i--; |
| 30 | |
| 31 | /* |
| 32 | * then go backwards until a slash, or the beginning of the |
| 33 | * string |
| 34 | */ |
| 35 | while (i && !is_dir_sep(path->buf[i - 1])) |
| 36 | i--; |
| 37 | |
| 38 | strbuf_setlen(path, i); |
| 39 | } |
| 40 | |
| 41 | |
| 42 | /* We allow "recursive" symbolic links. Only within reason, though */ |
| 43 | #define MAXDEPTH 5 |
| 44 | |
| 45 | /* |
| 46 | * path contains a path that might be a symlink. |
| 47 | * |
| 48 | * If path is a symlink, attempt to overwrite it with a path to the |
| 49 | * real file or directory (which may or may not exist), following a |
| 50 | * chain of symlinks if necessary. Otherwise, leave path unmodified. |
| 51 | * |
| 52 | * This is a best-effort routine. If an error occurs, path will |
| 53 | * either be left unmodified or will name a different symlink in a |
| 54 | * symlink chain that started with the original path. |
| 55 | */ |
| 56 | static void resolve_symlink(struct strbuf *path) |
| 57 | { |
| 58 | int depth = MAXDEPTH; |
| 59 | static struct strbuf link = STRBUF_INIT; |
| 60 | |
| 61 | while (depth--) { |
| 62 | if (strbuf_readlink(&link, path->buf, path->len) < 0) |
| 63 | break; |
| 64 | |
| 65 | if (is_absolute_path(link.buf)) |
| 66 | /* absolute path simply replaces p */ |
| 67 | strbuf_reset(path); |
| 68 | else |
| 69 | /* |
| 70 | * link is a relative path, so replace the |
| 71 | * last element of p with it. |
| 72 | */ |
| 73 | trim_last_path_component(path); |
| 74 | |
| 75 | strbuf_addbuf(path, &link); |
| 76 | } |
| 77 | strbuf_reset(&link); |
| 78 | } |
| 79 | |
| 80 | /* |
| 81 | * Lock PID file functions - write PID to a foo~pid.lock file alongside |
| 82 | * the lock file for debugging stale locks. The PID file is registered |
| 83 | * as a tempfile so it gets cleaned up by signal/atexit handlers. |
| 84 | * |
| 85 | * Naming: For "foo.lock", the PID file is "foo~pid.lock". The tilde is |
| 86 | * forbidden in refnames and allowed in Windows filenames, guaranteeing |
| 87 | * no collision with the refs namespace. |
| 88 | */ |
| 89 | |
| 90 | /* Global config variable, initialized from core.lockfilePid */ |
| 91 | int lockfile_pid_enabled; |
| 92 | |
| 93 | /* |
| 94 | * Path generation helpers. |
| 95 | * Given base path "foo", generate: |
| 96 | * - lock path: "foo.lock" |
| 97 | * - pid path: "foo-pid.lock" |
| 98 | */ |
| 99 | static void get_lock_path(struct strbuf *out, const char *path) |
| 100 | { |
| 101 | strbuf_addstr(out, path); |
| 102 | strbuf_addstr(out, LOCK_SUFFIX); |
| 103 | } |
| 104 | |
| 105 | static void get_pid_path(struct strbuf *out, const char *path) |
| 106 | { |
| 107 | strbuf_addstr(out, path); |
| 108 | strbuf_addstr(out, LOCK_PID_INFIX); |
| 109 | strbuf_addstr(out, LOCK_SUFFIX); |
| 110 | } |
| 111 | |
| 112 | static struct tempfile *create_lock_pid_file(const char *pid_path, int mode) |
| 113 | { |
| 114 | struct strbuf content = STRBUF_INIT; |
| 115 | struct tempfile *pid_tempfile = NULL; |
| 116 | int fd; |
| 117 | |
| 118 | if (!lockfile_pid_enabled) |
| 119 | goto out; |
| 120 | |
| 121 | fd = open(pid_path, O_WRONLY | O_CREAT | O_EXCL, mode); |
| 122 | if (fd < 0) |
| 123 | goto out; |
| 124 | |
| 125 | strbuf_addf(&content, "pid %" PRIuMAX "\n", (uintmax_t)getpid()); |
| 126 | if (write_in_full(fd, content.buf, content.len) < 0) { |
| 127 | warning_errno(_("could not write lock pid file '%s'"), pid_path); |
| 128 | close(fd); |
| 129 | unlink(pid_path); |
| 130 | goto out; |
| 131 | } |
| 132 | |
| 133 | close(fd); |
| 134 | pid_tempfile = register_tempfile(pid_path); |
| 135 | |
| 136 | out: |
| 137 | strbuf_release(&content); |
| 138 | return pid_tempfile; |
| 139 | } |
| 140 | |
| 141 | static int read_lock_pid(const char *pid_path, uintmax_t *pid_out) |
| 142 | { |
| 143 | struct strbuf content = STRBUF_INIT; |
| 144 | const char *val; |
| 145 | int ret = -1; |
| 146 | |
| 147 | if (strbuf_read_file(&content, pid_path, LOCK_PID_MAXLEN) <= 0) |
| 148 | goto out; |
| 149 | |
| 150 | strbuf_rtrim(&content); |
| 151 | |
| 152 | if (skip_prefix(content.buf, "pid ", &val)) { |
| 153 | char *endptr; |
| 154 | *pid_out = strtoumax(val, &endptr, 10); |
| 155 | if (*pid_out > 0 && !*endptr) |
| 156 | ret = 0; |
| 157 | } |
| 158 | |
| 159 | if (ret) |
| 160 | warning(_("malformed lock pid file '%s'"), pid_path); |
| 161 | |
| 162 | out: |
| 163 | strbuf_release(&content); |
| 164 | return ret; |
| 165 | } |
| 166 | |
| 167 | /* Make sure errno contains a meaningful value on error */ |
| 168 | static int lock_file(struct repository *r, struct lock_file *lk, |
| 169 | const char *path, int flags, int mode) |
| 170 | { |
| 171 | struct strbuf base_path = STRBUF_INIT; |
| 172 | struct strbuf lock_path = STRBUF_INIT; |
| 173 | struct strbuf pid_path = STRBUF_INIT; |
| 174 | |
| 175 | strbuf_addstr(&base_path, path); |
| 176 | if (!(flags & LOCK_NO_DEREF)) |
| 177 | resolve_symlink(&base_path); |
| 178 | |
| 179 | get_lock_path(&lock_path, base_path.buf); |
| 180 | get_pid_path(&pid_path, base_path.buf); |
| 181 | |
| 182 | lk->tempfile = repo_create_tempfile_mode(r, lock_path.buf, mode); |
| 183 | if (lk->tempfile) |
| 184 | lk->pid_tempfile = create_lock_pid_file(pid_path.buf, mode); |
| 185 | |
| 186 | strbuf_release(&base_path); |
| 187 | strbuf_release(&lock_path); |
| 188 | strbuf_release(&pid_path); |
| 189 | return lk->tempfile ? lk->tempfile->fd : -1; |
| 190 | } |
| 191 | |
| 192 | /* |
| 193 | * Constants defining the gaps between attempts to lock a file. The |
| 194 | * first backoff period is approximately INITIAL_BACKOFF_MS |
| 195 | * milliseconds. The longest backoff period is approximately |
| 196 | * (BACKOFF_MAX_MULTIPLIER * INITIAL_BACKOFF_MS) milliseconds. |
| 197 | */ |
| 198 | #define INITIAL_BACKOFF_MS 1L |
| 199 | #define BACKOFF_MAX_MULTIPLIER 1000 |
| 200 | |
| 201 | /* |
| 202 | * Try locking path, retrying with quadratic backoff for at least |
| 203 | * timeout_ms milliseconds. If timeout_ms is 0, try locking the file |
| 204 | * exactly once. If timeout_ms is -1, try indefinitely. |
| 205 | */ |
| 206 | static int lock_file_timeout(struct repository *r, struct lock_file *lk, |
| 207 | const char *path, int flags, long timeout_ms, |
| 208 | int mode) |
| 209 | { |
| 210 | int n = 1; |
| 211 | int multiplier = 1; |
| 212 | long remaining_ms = 0; |
| 213 | static int random_initialized = 0; |
| 214 | |
| 215 | if (timeout_ms == 0) |
| 216 | return lock_file(r, lk, path, flags, mode); |
| 217 | |
| 218 | if (!random_initialized) { |
| 219 | srand((unsigned int)getpid()); |
| 220 | random_initialized = 1; |
| 221 | } |
| 222 | |
| 223 | if (timeout_ms > 0) |
| 224 | remaining_ms = timeout_ms; |
| 225 | |
| 226 | while (1) { |
| 227 | long backoff_ms, wait_ms; |
| 228 | int fd; |
| 229 | |
| 230 | fd = lock_file(r, lk, path, flags, mode); |
| 231 | |
| 232 | if (fd >= 0) |
| 233 | return fd; /* success */ |
| 234 | else if (errno != EEXIST) |
| 235 | return -1; /* failure other than lock held */ |
| 236 | else if (timeout_ms > 0 && remaining_ms <= 0) |
| 237 | return -1; /* failure due to timeout */ |
| 238 | |
| 239 | backoff_ms = multiplier * INITIAL_BACKOFF_MS; |
| 240 | /* back off for between 0.75*backoff_ms and 1.25*backoff_ms */ |
| 241 | wait_ms = (750 + rand() % 500) * backoff_ms / 1000; |
| 242 | sleep_millisec(wait_ms); |
| 243 | remaining_ms -= wait_ms; |
| 244 | |
| 245 | /* Recursion: (n+1)^2 = n^2 + 2n + 1 */ |
| 246 | multiplier += 2*n + 1; |
| 247 | if (multiplier > BACKOFF_MAX_MULTIPLIER) |
| 248 | multiplier = BACKOFF_MAX_MULTIPLIER; |
| 249 | else |
| 250 | n++; |
| 251 | } |
| 252 | } |
| 253 | |
| 254 | void unable_to_lock_message(const char *path, int err, struct strbuf *buf) |
| 255 | { |
| 256 | if (err == EEXIST) { |
| 257 | const char *abs_path = absolute_path(path); |
| 258 | struct strbuf lock_path = STRBUF_INIT; |
| 259 | struct strbuf pid_path = STRBUF_INIT; |
| 260 | uintmax_t pid; |
| 261 | int pid_status = 0; /* 0 = unknown, 1 = running, -1 = stale */ |
| 262 | |
| 263 | get_lock_path(&lock_path, abs_path); |
| 264 | get_pid_path(&pid_path, abs_path); |
| 265 | |
| 266 | strbuf_addf(buf, _("Unable to create '%s': %s.\n\n"), |
| 267 | lock_path.buf, strerror(err)); |
| 268 | |
| 269 | /* |
| 270 | * Try to read PID file unconditionally - it may exist if |
| 271 | * core.lockfilePid was enabled. |
| 272 | */ |
| 273 | if (!read_lock_pid(pid_path.buf, &pid)) { |
| 274 | if (kill((pid_t)pid, 0) == 0 || errno == EPERM) |
| 275 | pid_status = 1; /* running (or no permission to signal) */ |
| 276 | else if (errno == ESRCH) |
| 277 | pid_status = -1; /* no such process - stale lock */ |
| 278 | } |
| 279 | |
| 280 | if (pid_status == 1) |
| 281 | strbuf_addf(buf, _("Lock may be held by process %" PRIuMAX "; " |
| 282 | "if no git process is running, the lock file " |
| 283 | "may be stale (PIDs can be reused)"), |
| 284 | pid); |
| 285 | else if (pid_status == -1) |
| 286 | strbuf_addf(buf, _("Lock was held by process %" PRIuMAX ", " |
| 287 | "which is no longer running; the lock file " |
| 288 | "appears to be stale"), |
| 289 | pid); |
| 290 | else |
| 291 | strbuf_addstr(buf, _("Another git process seems to be running in this repository, " |
| 292 | "or the lock file may be stale")); |
| 293 | |
| 294 | strbuf_release(&lock_path); |
| 295 | strbuf_release(&pid_path); |
| 296 | } else { |
| 297 | strbuf_addf(buf, _("Unable to create '%s.lock': %s"), |
| 298 | absolute_path(path), strerror(err)); |
| 299 | } |
| 300 | } |
| 301 | |
| 302 | NORETURN void unable_to_lock_die(const char *path, int err) |
| 303 | { |
| 304 | struct strbuf buf = STRBUF_INIT; |
| 305 | |
| 306 | unable_to_lock_message(path, err, &buf); |
| 307 | die("%s", buf.buf); |
| 308 | } |
| 309 | |
| 310 | /* This should return a meaningful errno on failure */ |
| 311 | int hold_lock_file_for_update_timeout_mode(struct lock_file *lk, |
| 312 | const char *path, int flags, |
| 313 | long timeout_ms, int mode) |
| 314 | { |
| 315 | return repo_hold_lock_file_for_update_timeout_mode(the_repository, |
| 316 | lk, path, flags, |
| 317 | timeout_ms, mode); |
| 318 | } |
| 319 | |
| 320 | int repo_hold_lock_file_for_update_timeout_mode(struct repository *r, |
| 321 | struct lock_file *lk, |
| 322 | const char *path, int flags, |
| 323 | long timeout_ms, int mode) |
| 324 | { |
| 325 | int fd = lock_file_timeout(r, lk, path, flags, timeout_ms, mode); |
| 326 | if (fd < 0) { |
| 327 | if (flags & LOCK_DIE_ON_ERROR) |
| 328 | unable_to_lock_die(path, errno); |
| 329 | if (flags & LOCK_REPORT_ON_ERROR) { |
| 330 | struct strbuf buf = STRBUF_INIT; |
| 331 | unable_to_lock_message(path, errno, &buf); |
| 332 | error("%s", buf.buf); |
| 333 | strbuf_release(&buf); |
| 334 | } |
| 335 | } |
| 336 | return fd; |
| 337 | } |
| 338 | |
| 339 | char *get_locked_file_path(struct lock_file *lk) |
| 340 | { |
| 341 | struct strbuf ret = STRBUF_INIT; |
| 342 | |
| 343 | strbuf_addstr(&ret, get_tempfile_path(lk->tempfile)); |
| 344 | if (ret.len <= LOCK_SUFFIX_LEN || |
| 345 | strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX)) |
| 346 | BUG("get_locked_file_path() called for malformed lock object"); |
| 347 | /* remove ".lock": */ |
| 348 | strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN); |
| 349 | return strbuf_detach(&ret, NULL); |
| 350 | } |
| 351 | |
| 352 | int commit_lock_file(struct lock_file *lk) |
| 353 | { |
| 354 | char *result_path = get_locked_file_path(lk); |
| 355 | |
| 356 | delete_tempfile(&lk->pid_tempfile); |
| 357 | |
| 358 | if (commit_lock_file_to(lk, result_path)) { |
| 359 | int save_errno = errno; |
| 360 | free(result_path); |
| 361 | errno = save_errno; |
| 362 | return -1; |
| 363 | } |
| 364 | free(result_path); |
| 365 | return 0; |
| 366 | } |
| 367 | |
| 368 | int rollback_lock_file(struct lock_file *lk) |
| 369 | { |
| 370 | delete_tempfile(&lk->pid_tempfile); |
| 371 | return delete_tempfile(&lk->tempfile); |
| 372 | } |