zvfs: introduce timerfd implementation

This add a timerfd-like interface similar to other systems.
Although this is not POSIX, it is very popular alternative to
POSIX timers.

The implementation is based on the current eventfd implementation,
with the relevant improvements and changes.

Add the ZVFS_TIMERFD so we can selectively enable/disable the
timerfd implementation.

Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>

Author: casaroli

include/zephyr/zvfs/timerfd.h

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2025 Atym, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_ZEPHYR_ZVFS_TIMERFD_H_
+#define ZEPHYR_INCLUDE_ZEPHYR_ZVFS_TIMERFD_H_
+
+#include <stdint.h>
+
+#include <zephyr/kernel.h>
+#include <zephyr/sys/timeutil.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define ZVFS_TFD_NONBLOCK 0x4000
+
+#define ZVFS_TFD_IOC_SET_TICKS 1
+
+typedef uint64_t zvfs_timerfd_t;
+
+/**
+ * @brief Create a file descriptor for ZVFS timer
+ *
+ * The returned file descriptor can be used with POSIX read calls or with
+ * the @ref zvfs_timerfd_* functions.
+ *
+ * It also supports polling and by including an timerfd in a call to poll,
+ * it is possible to signal and wake the polling thread when the timer
+ * expires.
+ *
+ * When using read() on a ZVFS timerfd, the size must always be at least
+ * 8 bytes or the operation will fail with EINVAL.
+ *
+ * @return New ZVFS timerfd file descriptor on success, -1 on error
+ */
+int zvfs_timerfd(unsigned int clockid, int flags);
+
+/**
+ * @brief Read from a ZVFS timerfd
+ *
+ * If call is successful, the value parameter will have the number of
+ * times the timer has expired since the last read.
+ *
+ * @param fd File descriptor
+ * @param value Pointer for storing the expired times value
+ *
+ * @return 0 on success, -1 on error
+ */
+int zvfs_timerfd_read(int fd, zvfs_timerfd_t *value);
+
+/**
+ * @brief Get the current value and period of a ZVFS timerfd.
+ *
+ * @param fd File descriptor
+ * @param remaining Pointer for storing the remaining milliseconds
+ * @param period Pointer for storing the period milliseconds
+ *
+ * @return 0 on success, -1 on error
+ */
+int zvfs_timerfd_gettime(int fd, uint32_t *remaining, uint32_t *period);
+
+/**
+ * @brief Set the value and period of a ZVFS timerfd.
+ *
+ * @param fd File descriptor
+ * @param duration Duration to write
+ * @param period Period to write
+ *
+ * @return 0 on success, -1 on error
+ */
+int zvfs_timerfd_settime(int fd, k_timeout_t duration, k_timeout_t period);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_ZEPHYR_ZVFS_TIMERFD_H_ */

lib/os/zvfs/CMakeLists.txt

@@ -2,5 +2,6 @@
 
 zephyr_library()
 zephyr_library_sources_ifdef(CONFIG_ZVFS_EVENTFD zvfs_eventfd.c)
+zephyr_library_sources_ifdef(CONFIG_ZVFS_TIMERFD zvfs_timerfd.c)
 zephyr_library_sources_ifdef(CONFIG_ZVFS_POLL zvfs_poll.c)
 zephyr_library_sources_ifdef(CONFIG_ZVFS_SELECT zvfs_select.c)

lib/os/zvfs/Kconfig

@@ -34,6 +34,25 @@ config ZVFS_EVENTFD_MAX
 
 endif # ZVFS_EVENTFD
 
+config ZVFS_TIMERFD
+	bool "ZVFS timer file descriptor support"
+	imply ZVFS_POLL
+	help
+	  Enable support for ZVFS timer file descriptors. An timerfd can
+	  be used as an event wait/notify mechanism together with POSIX calls
+	  like read, write and poll.
+
+if ZVFS_TIMERFD
+
+config ZVFS_TIMERFD_MAX
+	int "Maximum number of ZVFS timerfd's"
+	default 1
+	range 1 4096
+	help
+	  The maximum number of supported timer file descriptors.
+
+endif # ZVFS_TIMERFD
+
 config ZVFS_POLL
 	bool "ZVFS poll"
 	select POLL