1 files changed, 399 insertions, 0 deletions
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 <kzak@redhat.com>
+ *
+ * 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 <sys/time.h>
+#include <time.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sys/file.h>
+
+#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 <time_t>] [--verbose] <datafile> <loops> "
+				"increment a number in datafile" },
+	{ NULL }
+	};
+
+	return mnt_run_test(tss, argc, argv);
+}
+
+#endif /* TEST_PROGRAM */