posix: add timerfd interface

This is a wrapper around zvfs_timerfd, so we provide a standard
POSIX "compatible" timerfd interface.

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

Author: casaroli

include/zephyr/posix/sys/timerfd.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2020 Tobias Svehagen
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_POSIX_SYS_TIMERFD_H_
+#define ZEPHYR_INCLUDE_POSIX_SYS_TIMERFD_H_
+
+#include <zephyr/zvfs/timerfd.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define TFD_NONBLOCK  ZVFS_TFD_NONBLOCK
+
+#define TFD_IOC_SET_TICKS ZVFS_TFD_IOC_SET_TICKS
+
+#define TFD_TIMER_ABSTIME 1
+
+typedef zvfs_timerfd_t timerfd_t;
+
+/**
+ * @brief Create a file descriptor for ZVFS timer notification
+ *
+ * The returned file descriptor can be used with POSIX read calls or
+ * with the @ref zvfs_timerfd_settime or @ref zvfs_timerfd_gettime 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 by simply writing to
+ * the timerfd.
+ *
+ * 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 timerfd_create(int clockid, int flags);
+
+/**
+ * @brief Get the itimespec configuration ZVFS timerfd
+ *
+ * @param fd File descriptor
+ * @param curr_value Pointer to struct itimerspec to store current value
+ *
+ * @return 0 on success, -1 on error
+ */
+int timerfd_gettime(int fd, struct itimerspec *curr_value);
+
+/**
+ * @brief Set the itimespec configuration ZVFS timerfd
+ *
+ * The current value is stored in old_value if it is not NULL.
+ *
+ * @param fd File descriptor
+ * @param new_value Pointer to struct itimerspec to set new value
+ * @param old_value Pointer to struct itimerspec to store old value
+ *
+ * @return 0 on success, -1 on error
+ */
+int timerfd_settime(int fd, int flags, const struct itimerspec *new_value,
+    struct itimerspec *old_value);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_POSIX_SYS_TIMERFD_H_ */

lib/posix/CMakeLists.txt

@@ -2,6 +2,7 @@
 
 # zephyr-keep-sorted-start
 add_subdirectory_ifdef(CONFIG_EVENTFD eventfd)
+add_subdirectory_ifdef(CONFIG_TIMERFD timerfd)
 add_subdirectory_ifdef(CONFIG_POSIX_C_LANG_SUPPORT_R c_lang_support_r)
 add_subdirectory_ifdef(CONFIG_POSIX_C_LIB_EXT c_lib_ext)
 add_subdirectory_ifdef(CONFIG_POSIX_SHELL shell)

lib/posix/Kconfig

@@ -42,3 +42,6 @@ endmenu
 
 # Eventfd Support (not officially POSIX)
 rsource "eventfd/Kconfig"
+
+# Timerfd Support (not officially POSIX)
+rsource "timerfd/Kconfig"

lib/posix/Kconfig.profile

@@ -15,6 +15,7 @@ config POSIX_API
 	select POSIX_AEP_REALTIME_MINIMAL # CLOCK_MONOTONIC, pthread_attr_setstack(), etc
 	select POSIX_NETWORKING if NETWORKING # inet_ntoa(), socket(), etc
 	imply EVENTFD # eventfd(), eventfd_read(), eventfd_write()
+	imply TIMERFD # timerfd_create(), timerfd_settime(), timerfd_gettime()
 	imply POSIX_FD_MGMT # open(), close(), read(), write()
 	imply POSIX_MULTI_PROCESS # sleep(), getpid(), etc
 	imply XSI_SINGLE_PROCESS # gettimeofday()

lib/posix/timerfd/CMakeLists.txt

@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library()
+zephyr_library_sources(timerfd.c)

lib/posix/timerfd/Kconfig

@@ -0,0 +1,12 @@
+# Copyright (c) 2025 Atym, Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+config TIMERFD
+	bool "Support for timerfd"
+	select ZVFS
+	select ZVFS_TIMERFD
+	help
+	  Enable support for timer file descriptors, timerfd. A timerfd can
+	  be used as an timer waiting mechanism together with POSIX calls
+	  like read, write and poll.

lib/posix/timerfd/timerfd.c

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2024, Tenstorrent AI ULC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "../options/posix_clock.h"
+#include <string.h>
+
+#include <zephyr/posix/sys/timerfd.h>
+#include <zephyr/zvfs/timerfd.h>
+
+int timerfd_create(int clockid, int flags)
+{
+    return zvfs_timerfd(clockid, flags);
+};
+
+int timerfd_gettime(int fd, struct itimerspec *curr_value)
+{
+    int ret;
+    uint32_t value, period;
+   	int32_t leftover;
+	int64_t nsecs, secs;
+
+    ret = zvfs_timerfd_gettime(fd, &value, &period);
+    if (ret != 0) {
+        return ret;
+    }
+
+    /* converts value */
+    secs =  value / MSEC_PER_SEC;
+	leftover = value - (secs * MSEC_PER_SEC);
+	nsecs = (int64_t)leftover * NSEC_PER_MSEC;
+	curr_value->it_value.tv_sec = (int32_t) secs;
+	curr_value->it_value.tv_nsec = (int32_t) nsecs;
+
+	/* converts period */
+	secs =  period / MSEC_PER_SEC;
+    leftover = period - (secs * MSEC_PER_SEC);
+    nsecs = (int64_t)leftover * NSEC_PER_MSEC;
+    curr_value->it_interval.tv_sec = (int32_t) secs;
+    curr_value->it_interval.tv_nsec = (int32_t) nsecs;
+
+    return 0;
+};
+
+int timerfd_settime(int fd, int flags, const struct	itimerspec *new_value,
+	   struct itimerspec *old_value)
+{
+    uint32_t period, duration, current;
+
+   	if (!timespec_is_valid(&new_value->it_interval) ||
+	    !timespec_is_valid(&new_value->it_value)) {
+		errno = EINVAL;
+		return -1;
+	}
+
+   	/*  Save time to expire and old reload value. */
+	if (old_value != NULL) {
+		timerfd_gettime(fd, old_value);
+	}
+
+	/* Calculate timer duration */
+	duration = ts_to_ms(&(new_value->it_value));
+
+	/* Calculate timer period */
+	period = ts_to_ms(&(new_value->it_interval));
+
+	if ((flags & TFD_TIMER_ABSTIME) != 0) {
+    	zvfs_timerfd_gettime(fd, &current, NULL);
+
+		if (current >= duration) {
+			duration = 0U;
+		} else {
+			duration -= current;
+		}
+	}
+
+    return zvfs_timerfd_settime(fd, K_MSEC(duration), K_MSEC(period));
+}