1 files changed, 530 insertions, 0 deletions

diff --git a/src/lib/file-lock.c b/src/lib/file-lock.c
new file mode 100644
index 0000000..f17beea
--- /dev/null
+++ b/src/lib/file-lock.c
@@ -0,0 +1,530 @@
+/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "istream.h"
+#include "file-lock.h"
+#include "file-dotlock.h"
+#include "time-util.h"
+
+#include <time.h>
+#include <sys/stat.h>
+#ifdef HAVE_FLOCK
+#  include <sys/file.h>
+#endif
+
+struct file_lock {
+	struct file_lock_settings set;
+
+	int fd;
+	char *path;
+	struct dotlock *dotlock;
+
+	struct timeval locked_time;
+	int lock_type;
+};
+
+static struct timeval lock_wait_start;
+static uint64_t file_lock_wait_usecs = 0;
+static long long file_lock_slow_warning_usecs = -1;
+
+static void file_lock_log_warning_if_slow(struct file_lock *lock);
+
+bool file_lock_method_parse(const char *name, enum file_lock_method *method_r)
+{
+	if (strcasecmp(name, "fcntl") == 0)
+		*method_r = FILE_LOCK_METHOD_FCNTL;
+	else if (strcasecmp(name, "flock") == 0)
+		*method_r = FILE_LOCK_METHOD_FLOCK;
+	else if (strcasecmp(name, "dotlock") == 0)
+		*method_r = FILE_LOCK_METHOD_DOTLOCK;
+	else
+		return FALSE;
+	return TRUE;
+}
+
+const char *file_lock_method_to_str(enum file_lock_method method)
+{
+	switch (method) {
+	case FILE_LOCK_METHOD_FCNTL:
+		return "fcntl";
+	case FILE_LOCK_METHOD_FLOCK:
+		return "flock";
+	case FILE_LOCK_METHOD_DOTLOCK:
+		return "dotlock";
+	}
+	i_unreached();
+}
+
+int file_try_lock(int fd, const char *path, int lock_type,
+		  const struct file_lock_settings *set,
+		  struct file_lock **lock_r, const char **error_r)
+{
+	return file_wait_lock(fd, path, lock_type, set, 0, lock_r, error_r);
+}
+
+static const char *
+file_lock_find_fcntl(int lock_fd, int lock_type)
+{
+	struct flock fl;
+
+	i_zero(&fl);
+	fl.l_type = lock_type;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = 0;
+	fl.l_len = 0;
+
+	if (fcntl(lock_fd, F_GETLK, &fl) < 0 ||
+	    fl.l_type == F_UNLCK || fl.l_pid == -1 || fl.l_pid == 0)
+		return "";
+	return t_strdup_printf(" (%s lock held by pid %ld)",
+		fl.l_type == F_RDLCK ? "READ" : "WRITE", (long)fl.l_pid);
+}
+
+static const char *
+file_lock_find_proc_locks(int lock_fd ATTR_UNUSED)
+{
+	/* do anything except Linux support this? don't bother trying it for
+	   OSes we don't know about. */
+#ifdef __linux__
+	static bool have_proc_locks = TRUE;
+	struct stat st;
+	char node_buf[MAX_INT_STRLEN * 3 + 2];
+	struct istream *input;
+	const char *line, *lock_type = "";
+	pid_t pid = 0;
+	int fd;
+
+	if (!have_proc_locks)
+		return NULL;
+
+	if (fstat(lock_fd, &st) < 0)
+		return "";
+	i_snprintf(node_buf, sizeof(node_buf), "%02x:%02x:%llu",
+		   major(st.st_dev), minor(st.st_dev),
+		   (unsigned long long)st.st_ino);
+	fd = open("/proc/locks", O_RDONLY);
+	if (fd == -1) {
+		have_proc_locks = FALSE;
+		return "";
+	}
+	input = i_stream_create_fd_autoclose(&fd, 512);
+	while (pid == 0 && (line = i_stream_read_next_line(input)) != NULL) T_BEGIN {
+		const char *const *args = t_strsplit_spaces(line, " ");
+
+		/* number: FLOCK/POSIX ADVISORY READ/WRITE pid
+		   major:minor:inode region-start region-end */
+		if (str_array_length(args) < 8) {
+			; /* don't continue from within a T_BEGIN {...} T_END */
+		} else if (strcmp(args[5], node_buf) == 0) {
+			lock_type = strcmp(args[3], "READ") == 0 ?
+				"READ" : "WRITE";
+			if (str_to_pid(args[4], &pid) < 0)
+				pid = 0;
+		}
+	} T_END;
+	i_stream_destroy(&input);
+	if (pid == 0) {
+		/* not found */
+		return "";
+	}
+	if (pid == getpid())
+		return " (BUG: lock is held by our own process)";
+	return t_strdup_printf(" (%s lock held by pid %ld)", lock_type, (long)pid);
+#else
+	return "";
+#endif
+}
+
+const char *file_lock_find(int lock_fd, enum file_lock_method lock_method,
+			   int lock_type)
+{
+	const char *ret;
+
+	if (lock_method == FILE_LOCK_METHOD_FCNTL) {
+		ret = file_lock_find_fcntl(lock_fd, lock_type);
+		if (ret[0] != '\0')
+			return ret;
+	}
+	return file_lock_find_proc_locks(lock_fd);
+}
+
+static bool err_is_lock_timeout(time_t started, unsigned int timeout_secs)
+{
+	/* if EINTR took at least timeout_secs-1 number of seconds,
+	   assume it was the alarm. otherwise log EINTR failure.
+	   (We most likely don't want to retry EINTR since a signal
+	   means somebody wants us to stop blocking). */
+	return errno == EINTR &&
+		(unsigned long)(time(NULL) - started + 1) >= timeout_secs;
+}
+
+static int file_lock_do(int fd, const char *path, int lock_type,
+			const struct file_lock_settings *set,
+			unsigned int timeout_secs, const char **error_r)
+{
+	const char *lock_type_str;
+	time_t started = time(NULL);
+	int ret;
+
+	i_assert(fd != -1);
+
+	if (timeout_secs != 0) {
+		alarm(timeout_secs);
+		file_lock_wait_start();
+	}
+
+	lock_type_str = lock_type == F_UNLCK ? "unlock" :
+		(lock_type == F_RDLCK ? "read-lock" : "write-lock");
+
+	switch (set->lock_method) {
+	case FILE_LOCK_METHOD_FCNTL: {
+#ifndef HAVE_FCNTL
+		*error_r = t_strdup_printf(
+			"Can't lock file %s: fcntl() locks not supported", path);
+		return -1;
+#else
+		struct flock fl;
+
+		fl.l_type = lock_type;
+		fl.l_whence = SEEK_SET;
+		fl.l_start = 0;
+		fl.l_len = 0;
+
+		ret = fcntl(fd, timeout_secs != 0 ? F_SETLKW : F_SETLK, &fl);
+		if (timeout_secs != 0) {
+			alarm(0);
+			file_lock_wait_end(path);
+		}
+
+		if (ret == 0)
+			break;
+
+		if (timeout_secs == 0 &&
+		    (errno == EACCES || errno == EAGAIN)) {
+			/* locked by another process */
+			*error_r = t_strdup_printf(
+				"fcntl(%s, %s, F_SETLK) locking failed: %m "
+				"(File is already locked)", path, lock_type_str);
+			return 0;
+		}
+
+		if (err_is_lock_timeout(started, timeout_secs)) {
+			errno = EAGAIN;
+			*error_r = t_strdup_printf(
+				"fcntl(%s, %s, F_SETLKW) locking failed: "
+				"Timed out after %u seconds%s",
+				path, lock_type_str, timeout_secs,
+				file_lock_find(fd, set->lock_method,
+					       lock_type));
+			return 0;
+		}
+		*error_r = t_strdup_printf("fcntl(%s, %s, %s) locking failed: %m",
+			path, lock_type_str, timeout_secs == 0 ? "F_SETLK" : "F_SETLKW");
+		if (errno == EDEADLK && !set->allow_deadlock) {
+			i_panic("%s%s", *error_r,
+				file_lock_find(fd, set->lock_method,
+					       lock_type));
+		}
+		return -1;
+#endif
+	}
+	case FILE_LOCK_METHOD_FLOCK: {
+#ifndef HAVE_FLOCK
+		*error_r = t_strdup_printf(
+			"Can't lock file %s: flock() not supported", path);
+		return -1;
+#else
+		int operation = timeout_secs != 0 ? 0 : LOCK_NB;
+
+		switch (lock_type) {
+		case F_RDLCK:
+			operation |= LOCK_SH;
+			break;
+		case F_WRLCK:
+			operation |= LOCK_EX;
+			break;
+		case F_UNLCK:
+			operation |= LOCK_UN;
+			break;
+		}
+
+		ret = flock(fd, operation);
+		if (timeout_secs != 0) {
+			alarm(0);
+			file_lock_wait_end(path);
+		}
+
+		if (ret == 0)
+			break;
+
+		if (timeout_secs == 0 && errno == EWOULDBLOCK) {
+			/* locked by another process */
+			*error_r = t_strdup_printf(
+				"flock(%s, %s) failed: %m "
+				"(File is already locked)", path, lock_type_str);
+			return 0;
+		}
+		if (err_is_lock_timeout(started, timeout_secs)) {
+			errno = EAGAIN;
+			*error_r = t_strdup_printf("flock(%s, %s) failed: "
+				"Timed out after %u seconds%s",
+				path, lock_type_str, timeout_secs,
+				file_lock_find(fd, set->lock_method,
+					       lock_type));
+			return 0;
+		}
+		*error_r = t_strdup_printf("flock(%s, %s) failed: %m",
+					   path, lock_type_str);
+		if (errno == EDEADLK && !set->allow_deadlock) {
+			i_panic("%s%s", *error_r,
+				file_lock_find(fd, set->lock_method,
+					       lock_type));
+		}
+		return -1;
+#endif
+	}
+	case FILE_LOCK_METHOD_DOTLOCK:
+		/* we shouldn't get here */
+		i_unreached();
+	}
+
+	return 1;
+}
+
+int file_wait_lock(int fd, const char *path, int lock_type,
+		   const struct file_lock_settings *set,
+		   unsigned int timeout_secs,
+		   struct file_lock **lock_r, const char **error_r)
+{
+	struct file_lock *lock;
+	int ret;
+
+	ret = file_lock_do(fd, path, lock_type, set, timeout_secs, error_r);
+	if (ret <= 0)
+		return ret;
+
+	lock = i_new(struct file_lock, 1);
+	lock->set = *set;
+	lock->fd = fd;
+	lock->path = i_strdup(path);
+	lock->lock_type = lock_type;
+	i_gettimeofday(&lock->locked_time);
+	*lock_r = lock;
+	return 1;
+}
+
+int file_lock_try_update(struct file_lock *lock, int lock_type)
+{
+	const char *error;
+	int ret;
+
+	ret = file_lock_do(lock->fd, lock->path, lock_type, &lock->set, 0,
+			   &error);
+	if (ret <= 0)
+		return ret;
+	file_lock_log_warning_if_slow(lock);
+	lock->lock_type = lock_type;
+	return 1;
+}
+
+void file_lock_set_unlink_on_free(struct file_lock *lock, bool set)
+{
+	lock->set.unlink_on_free = set;
+}
+
+void file_lock_set_close_on_free(struct file_lock *lock, bool set)
+{
+	lock->set.close_on_free = set;
+}
+
+struct file_lock *file_lock_from_dotlock(struct dotlock **dotlock)
+{
+	struct file_lock *lock;
+
+	lock = i_new(struct file_lock, 1);
+	lock->set.lock_method = FILE_LOCK_METHOD_DOTLOCK;
+	lock->fd = -1;
+	lock->path = i_strdup(file_dotlock_get_lock_path(*dotlock));
+	lock->lock_type = F_WRLCK;
+	i_gettimeofday(&lock->locked_time);
+	lock->dotlock = *dotlock;
+
+	*dotlock = NULL;
+	return lock;
+}
+
+static void file_unlock_real(struct file_lock *lock)
+{
+	const char *error;
+
+	if (file_lock_do(lock->fd, lock->path, F_UNLCK, &lock->set, 0,
+			 &error) == 0) {
+		/* this shouldn't happen */
+		i_error("file_unlock(%s) failed: %m", lock->path);
+	}
+}
+
+void file_unlock(struct file_lock **_lock)
+{
+	struct file_lock *lock = *_lock;
+
+	*_lock = NULL;
+
+	/* unlocking is unnecessary when the file is unlinked. or alternatively
+	   the unlink() must be done before unlocking, because otherwise it
+	   could be deleting the new lock. */
+	i_assert(!lock->set.unlink_on_free);
+
+	if (lock->dotlock == NULL)
+		file_unlock_real(lock);
+	file_lock_free(&lock);
+}
+
+static void file_try_unlink_locked(struct file_lock *lock)
+{
+	struct file_lock *temp_lock = NULL;
+	struct file_lock_settings temp_set = lock->set;
+	struct stat st1, st2;
+	const char *error;
+	int ret;
+
+	temp_set.close_on_free = FALSE;
+	temp_set.unlink_on_free = FALSE;
+
+	file_unlock_real(lock);
+	ret = file_try_lock(lock->fd, lock->path, F_WRLCK, &temp_set,
+			    &temp_lock, &error);
+	if (ret < 0) {
+		i_error("file_lock_free(): Unexpectedly failed to retry locking %s: %s",
+			lock->path, error);
+	} else if (ret == 0) {
+		/* already locked by someone else */
+	} else if (fstat(lock->fd, &st1) < 0) {
+		/* not expected to happen */
+		i_error("file_lock_free(): fstat(%s) failed: %m", lock->path);
+	} else if (stat(lock->path, &st2) < 0) {
+		if (errno != ENOENT)
+			i_error("file_lock_free(): stat(%s) failed: %m", lock->path);
+	} else if (st1.st_ino != st2.st_ino ||
+		   !CMP_DEV_T(st1.st_dev, st2.st_dev)) {
+		/* lock file was recreated already - don't delete it */
+	} else {
+		/* nobody was waiting on the lock - unlink it */
+		i_unlink(lock->path);
+	}
+	file_lock_free(&temp_lock);
+}
+
+void file_lock_free(struct file_lock **_lock)
+{
+	struct file_lock *lock = *_lock;
+
+	if (lock == NULL)
+		return;
+
+	*_lock = NULL;
+
+	if (lock->dotlock != NULL)
+		file_dotlock_delete(&lock->dotlock);
+	if (lock->set.unlink_on_free)
+		file_try_unlink_locked(lock);
+	if (lock->set.close_on_free)
+		i_close_fd(&lock->fd);
+
+	file_lock_log_warning_if_slow(lock);
+	i_free(lock->path);
+	i_free(lock);
+}
+
+const char *file_lock_get_path(struct file_lock *lock)
+{
+	return lock->path;
+}
+
+void file_lock_set_path(struct file_lock *lock, const char *path)
+{
+	if (path != lock->path) {
+		i_free(lock->path);
+		lock->path = i_strdup(path);
+	}
+}
+
+void file_lock_wait_start(void)
+{
+	i_assert(lock_wait_start.tv_sec == 0);
+
+	i_gettimeofday(&lock_wait_start);
+}
+
+static void file_lock_wait_init_warning(void)
+{
+	const char *value;
+
+	i_assert(file_lock_slow_warning_usecs == -1);
+
+	value = getenv("FILE_LOCK_SLOW_WARNING_MSECS");
+	if (value == NULL)
+		file_lock_slow_warning_usecs = LLONG_MAX;
+	else if (str_to_llong(value, &file_lock_slow_warning_usecs) == 0 &&
+		 file_lock_slow_warning_usecs > 0) {
+		file_lock_slow_warning_usecs *= 1000;
+	} else {
+		i_error("FILE_LOCK_SLOW_WARNING_MSECS: "
+			"Invalid value '%s' - ignoring", value);
+		file_lock_slow_warning_usecs = LLONG_MAX;
+	}
+}
+
+static void file_lock_log_warning_if_slow(struct file_lock *lock)
+{
+	if (file_lock_slow_warning_usecs < 0)
+		file_lock_wait_init_warning();
+	if (file_lock_slow_warning_usecs == LLONG_MAX) {
+		/* slowness checking is disabled */
+		return;
+	}
+	if (lock->lock_type != F_WRLCK) {
+		/* some shared locks can legitimately be kept for a long time.
+		   don't warn about them. */
+		return;
+	}
+
+	struct timeval now;
+	i_gettimeofday(&now);
+
+	int diff = timeval_diff_msecs(&now, &lock->locked_time);
+	if (diff > file_lock_slow_warning_usecs/1000) {
+		i_warning("Lock %s kept for %d.%03d secs", lock->path,
+			  diff / 1000, diff % 1000);
+	}
+}
+
+void file_lock_wait_end(const char *lock_name)
+{
+	struct timeval now;
+
+	i_assert(lock_wait_start.tv_sec != 0);
+
+	i_gettimeofday(&now);
+	long long diff = timeval_diff_usecs(&now, &lock_wait_start);
+	if (diff < 0) {
+		/* time moved backwards */
+		diff = 0;
+	}
+	if (diff > file_lock_slow_warning_usecs) {
+		if (file_lock_slow_warning_usecs < 0)
+			file_lock_wait_init_warning();
+		if (diff > file_lock_slow_warning_usecs) {
+			int diff_msecs = (diff + 999) / 1000;
+			i_warning("Locking %s took %d.%03d secs", lock_name,
+				  diff_msecs / 1000, diff_msecs % 1000);
+		}
+	}
+	file_lock_wait_usecs += diff;
+	lock_wait_start.tv_sec = 0;
+}
+
+uint64_t file_lock_wait_get_total_usecs(void)
+{
+	return file_lock_wait_usecs;
+}