From cfe5e3905201349e9cf3f95d52ff4bd100bde37d Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 14 Apr 2024 21:10:49 +0200 Subject: Adding upstream version 2.39.3. Signed-off-by: Daniel Baumann --- libmount/src/lock.c | 399 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 399 insertions(+) create mode 100644 libmount/src/lock.c (limited to 'libmount/src/lock.c') diff --git a/libmount/src/lock.c b/libmount/src/lock.c new file mode 100644 index 0000000..4835406 --- /dev/null +++ b/libmount/src/lock.c @@ -0,0 +1,399 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ +/* + * This file is part of libmount from util-linux project. + * + * Copyright (C) 2009-2018 Karel Zak + * + * libmount is free software; you can redistribute it and/or modify it + * under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or + * (at your option) any later version. + */ + +/** + * SECTION: lock + * @title: Locking + * @short_description: locking methods for utab or another libmount files + * + * Since v2.39 libmount does nto support classic mtab locking. Now all is based + * on flock only. + * + */ +#include +#include +#include +#include +#include +#include + +#include "strutils.h" +#include "closestream.h" +#include "pathnames.h" +#include "mountP.h" +#include "monotonic.h" + +/* + * lock handler + */ +struct libmnt_lock { + char *lockfile; /* path to lock file (e.g. /etc/mtab~) */ + int lockfile_fd; /* lock file descriptor */ + + unsigned int locked :1, /* do we own the lock? */ + sigblock :1; /* block signals when locked */ + + sigset_t oldsigmask; +}; + + +/** + * mnt_new_lock: + * @datafile: the file that should be covered by the lock + * @id: ignored by library + * + * Returns: newly allocated lock handler or NULL on case of error. + */ +struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id __attribute__((__unused__))) +{ + struct libmnt_lock *ml = NULL; + char *lo = NULL; + size_t losz; + + if (!datafile) + return NULL; + + losz = strlen(datafile) + sizeof(".lock"); + lo = malloc(losz); + if (!lo) + goto err; + + snprintf(lo, losz, "%s.lock", datafile); + + ml = calloc(1, sizeof(*ml) ); + if (!ml) + goto err; + + ml->lockfile_fd = -1; + ml->lockfile = lo; + + DBG(LOCKS, ul_debugobj(ml, "alloc: lockfile=%s", lo)); + return ml; +err: + free(lo); + free(ml); + return NULL; +} + + +/** + * mnt_free_lock: + * @ml: struct libmnt_lock handler + * + * Deallocates mnt_lock. + */ +void mnt_free_lock(struct libmnt_lock *ml) +{ + if (!ml) + return; + DBG(LOCKS, ul_debugobj(ml, "free%s", ml->locked ? " !!! LOCKED !!!" : "")); + free(ml->lockfile); + free(ml); +} + +/** + * mnt_lock_block_signals: + * @ml: struct libmnt_lock handler + * @enable: TRUE/FALSE + * + * Block/unblock signals when the lock is locked, the signals are not blocked + * by default. + * + * Returns: <0 on error, 0 on success. + */ +int mnt_lock_block_signals(struct libmnt_lock *ml, int enable) +{ + if (!ml) + return -EINVAL; + DBG(LOCKS, ul_debugobj(ml, "signals: %s", enable ? "BLOCKED" : "UNBLOCKED")); + ml->sigblock = enable ? 1 : 0; + return 0; +} + +/* + * Returns path to lockfile. + */ +static const char *mnt_lock_get_lockfile(struct libmnt_lock *ml) +{ + return ml ? ml->lockfile : NULL; +} + +/* + * Simple flocking + */ +static void unlock_simplelock(struct libmnt_lock *ml) +{ + assert(ml); + + if (ml->lockfile_fd >= 0) { + DBG(LOCKS, ul_debugobj(ml, "%s: unflocking", + mnt_lock_get_lockfile(ml))); + close(ml->lockfile_fd); + } +} + +static int lock_simplelock(struct libmnt_lock *ml) +{ + const char *lfile; + int rc; + struct stat sb; + const mode_t lock_mask = S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH; + + assert(ml); + + lfile = mnt_lock_get_lockfile(ml); + + DBG(LOCKS, ul_debugobj(ml, "%s: locking", lfile)); + + if (ml->sigblock) { + sigset_t sigs; + sigemptyset(&ml->oldsigmask); + sigfillset(&sigs); + sigprocmask(SIG_BLOCK, &sigs, &ml->oldsigmask); + } + + ml->lockfile_fd = open(lfile, O_RDONLY|O_CREAT|O_CLOEXEC, + S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH); + if (ml->lockfile_fd < 0) { + rc = -errno; + goto err; + } + + rc = fstat(ml->lockfile_fd, &sb); + if (rc < 0) { + rc = -errno; + goto err; + } + + if ((sb.st_mode & lock_mask) != lock_mask) { + rc = fchmod(ml->lockfile_fd, lock_mask); + if (rc < 0) { + rc = -errno; + goto err; + } + } + + while (flock(ml->lockfile_fd, LOCK_EX) < 0) { + int errsv; + if ((errno == EAGAIN) || (errno == EINTR)) + continue; + errsv = errno; + close(ml->lockfile_fd); + ml->lockfile_fd = -1; + rc = -errsv; + goto err; + } + ml->locked = 1; + return 0; +err: + if (ml->sigblock) + sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL); + return rc; +} + +/** + * mnt_lock_file + * @ml: pointer to struct libmnt_lock instance + * + * Creates a lock file. +* + * Note that when the lock is used by mnt_update_table() interface then libmount + * uses flock() for private library file /run/mount/utab. + * + * Returns: 0 on success or negative number in case of error (-ETIMEOUT is case + * of stale lock file). + */ +int mnt_lock_file(struct libmnt_lock *ml) +{ + if (!ml) + return -EINVAL; + + return lock_simplelock(ml); +} + +/** + * mnt_unlock_file: + * @ml: lock struct + * + * Unlocks the file. The function could be called independently of the + * lock status (for example from exit(3)). + */ +void mnt_unlock_file(struct libmnt_lock *ml) +{ + if (!ml) + return; + + DBG(LOCKS, ul_debugobj(ml, "(%d) %s", getpid(), + ml->locked ? "unlocking" : "cleaning")); + + unlock_simplelock(ml); + + ml->locked = 0; + ml->lockfile_fd = -1; + + if (ml->sigblock) { + DBG(LOCKS, ul_debugobj(ml, "restoring sigmask")); + sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL); + } +} + +#ifdef TEST_PROGRAM + +static struct libmnt_lock *lock; + +/* + * read number from @filename, increment the number and + * write the number back to the file + */ +static void increment_data(const char *filename, int verbose, int loopno) +{ + long num; + FILE *f; + char buf[256]; + + if (!(f = fopen(filename, "r" UL_CLOEXECSTR))) + err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename); + + if (!fgets(buf, sizeof(buf), f)) + err(EXIT_FAILURE, "%d failed read: %s", getpid(), filename); + + fclose(f); + num = atol(buf) + 1; + + if (!(f = fopen(filename, "w" UL_CLOEXECSTR))) + err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename); + + fprintf(f, "%ld", num); + + if (close_stream(f) != 0) + err(EXIT_FAILURE, "write failed: %s", filename); + + if (verbose) + fprintf(stderr, "%d: %s: %ld --> %ld (loop=%d)\n", getpid(), + filename, num - 1, num, loopno); +} + +static void clean_lock(void) +{ + if (!lock) + return; + mnt_unlock_file(lock); + mnt_free_lock(lock); +} + +static void __attribute__((__noreturn__)) sig_handler(int sig) +{ + errx(EXIT_FAILURE, "\n%d: catch signal: %s\n", getpid(), strsignal(sig)); +} + +static int test_lock(struct libmnt_test *ts, int argc, char *argv[]) +{ + time_t synctime = 0; + unsigned int usecs; + const char *datafile = NULL; + int verbose = 0, loops = 0, l, idx = 1; + + if (argc < 3) + return -EINVAL; + + if (strcmp(argv[idx], "--synctime") == 0) { + synctime = (time_t) atol(argv[idx + 1]); + idx += 2; + } + if (idx < argc && strcmp(argv[idx], "--verbose") == 0) { + verbose = 1; + idx++; + } + + if (idx < argc) + datafile = argv[idx++]; + if (idx < argc) + loops = atoi(argv[idx++]); + + if (!datafile || !loops) + return -EINVAL; + + if (verbose) + fprintf(stderr, "%d: start: synctime=%u, datafile=%s, loops=%d\n", + getpid(), (int) synctime, datafile, loops); + + atexit(clean_lock); + + /* be paranoid and call exit() (=clean_lock()) for all signals */ + { + int sig = 0; + struct sigaction sa; + + sa.sa_handler = sig_handler; + sa.sa_flags = 0; + sigfillset(&sa.sa_mask); + + while (sigismember(&sa.sa_mask, ++sig) != -1 && sig != SIGCHLD) + sigaction (sig, &sa, (struct sigaction *) 0); + } + + /* start the test in exactly defined time */ + if (synctime) { + struct timeval tv; + + gettimeofday(&tv, NULL); + if (synctime && synctime - tv.tv_sec > 1) { + usecs = ((synctime - tv.tv_sec) * 1000000UL) - + (1000000UL - tv.tv_usec); + xusleep(usecs); + } + } + + for (l = 0; l < loops; l++) { + lock = mnt_new_lock(datafile, 0); + if (!lock) + return -1; + + if (mnt_lock_file(lock) != 0) { + fprintf(stderr, "%d: failed to lock %s file\n", + getpid(), datafile); + return -1; + } + + increment_data(datafile, verbose, l); + + mnt_unlock_file(lock); + mnt_free_lock(lock); + lock = NULL; + + /* The mount command usually finishes after a mtab update. We + * simulate this via short sleep -- it's also enough to make + * concurrent processes happy. + */ + if (synctime) + xusleep(25000); + } + + return 0; +} + +/* + * Note that this test should be executed from a script that creates many + * parallel processes, otherwise this test does not make sense. + */ +int main(int argc, char *argv[]) +{ + struct libmnt_test tss[] = { + { "--lock", test_lock, " [--synctime ] [--verbose] " + "increment a number in datafile" }, + { NULL } + }; + + return mnt_run_test(tss, argc, argv); +} + +#endif /* TEST_PROGRAM */ -- cgit v1.2.3