posix: options: implement the POSIX_FILE_LOCKING Option Group

Provide an implementation of the POSIX_FILE_LOCKING Option
Group.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>

Author: cfriedt

lib/libc/Kconfig

@@ -86,6 +86,7 @@ config PICOLIBC
 	select LIBC_ERRNO if THREAD_LOCAL_STORAGE
 	select NEED_LIBC_MEM_PARTITION
 	select TC_PROVIDES_POSIX_C_LANG_SUPPORT_R
+	select TC_PROVIDES_POSIX_FILE_LOCKING
 	imply COMMON_LIBC_MALLOC
 	depends on PICOLIBC_SUPPORTED
 	help

lib/os/fdtable.c

@@ -339,43 +339,37 @@ static bool supports_pread_pwrite(uint32_t mode)
 	}
 }
 
-static ssize_t zvfs_rw(int fd, void *buf, size_t sz, bool is_write, const size_t *from_offset)
+static ssize_t zvfs_rw_unlocked(int fd, void *buf, size_t sz, bool is_write,
+				const size_t *from_offset)
 {
 	bool prw;
 	ssize_t res;
 	const size_t *off;
 
-	if (_check_fd(fd) < 0) {
-		return -1;
-	}
-
-	(void)k_mutex_lock(&fdtable[fd].lock, K_FOREVER);
-
 	prw = supports_pread_pwrite(fdtable[fd].mode);
 	if (from_offset != NULL && !prw) {
 		/*
 		 * Seekable file types should support pread() / pwrite() and per-fd offset passing.
 		 * Otherwise, it's a bug.
 		 */
 		errno = ENOTSUP;
-		res = -1;
-		goto unlock;
+		return -1;
 	}
 
 	/* If there is no specified from_offset, then use the current offset of the fd */
 	off = (from_offset == NULL) ? &fdtable[fd].offset : from_offset;
 
 	if (is_write) {
 		if (fdtable[fd].vtable->write_offs == NULL) {
-			res = -1;
 			errno = EIO;
+			return -1;
 		} else {
 			res = fdtable[fd].vtable->write_offs(fdtable[fd].obj, buf, sz, *off);
 		}
 	} else {
 		if (fdtable[fd].vtable->read_offs == NULL) {
-			res = -1;
 			errno = EIO;
+			return -1;
 		} else {
 			res = fdtable[fd].vtable->read_offs(fdtable[fd].obj, buf, sz, *off);
 		}
@@ -388,7 +382,21 @@ static ssize_t zvfs_rw(int fd, void *buf, size_t sz, bool is_write, const size_t
 		fdtable[fd].offset += res;
 	}
 
-unlock:
+	return res;
+}
+
+static ssize_t zvfs_rw(int fd, void *buf, size_t sz, bool is_write, const size_t *from_offset)
+{
+	ssize_t res;
+
+	if (_check_fd(fd) < 0) {
+		return -1;
+	}
+
+	(void)k_mutex_lock(&fdtable[fd].lock, K_FOREVER);
+
+	res = zvfs_rw_unlocked(fd, buf, sz, is_write, from_offset);
+
 	k_mutex_unlock(&fdtable[fd].lock);
 
 	return res;
@@ -562,6 +570,81 @@ int zvfs_ioctl(int fd, unsigned long request, va_list args)
 	return fdtable[fd].vtable->ioctl(fdtable[fd].obj, request, args);
 }
 
+int zvfs_lock_file(FILE *file, k_timeout_t timeout)
+{
+	int fd;
+	int prev_errno;
+	struct fd_entry *entry;
+
+	fd = z_libc_file_get_fd(file);
+	prev_errno = errno;
+	if (_check_fd(fd) < 0) {
+		if (errno != prev_errno) {
+			errno = prev_errno;
+		}
+		return -1;
+	}
+
+	entry = &fdtable[fd];
+	return k_mutex_lock(&entry->lock, timeout);
+}
+
+int zvfs_unlock_file(FILE *file)
+{
+	int fd;
+	int prev_errno;
+	struct fd_entry *entry;
+
+	fd = z_libc_file_get_fd(file);
+	prev_errno = errno;
+	if (_check_fd(fd) < 0) {
+		if (errno != prev_errno) {
+			errno = prev_errno;
+		}
+		return -1;
+	}
+
+	entry = &fdtable[fd];
+	return k_mutex_unlock(&entry->lock);
+}
+
+int zvfs_getc_unlocked(FILE *stream)
+{
+	int fd;
+	int res;
+	char buf;
+
+	fd = z_libc_file_get_fd(stream);
+	if (_check_fd(fd) < 0) {
+		return EOF;
+	}
+
+	res = zvfs_rw_unlocked(fd, &buf, 1, false, NULL);
+	if (res <= 0) {
+		return EOF;
+	}
+
+	return (int)buf;
+}
+
+int zvfs_putc_unlocked(int c, FILE *stream)
+{
+	int fd;
+	int res;
+	char buf = (char)c;
+
+	fd = z_libc_file_get_fd(stream);
+	if (_check_fd(fd) < 0) {
+		return EOF;
+	}
+
+	res = zvfs_rw_unlocked(fd, &buf, 1, true, NULL);
+	if (res <= 0) {
+		return EOF;
+	}
+
+	return c;
+}
 
 #if defined(CONFIG_POSIX_DEVICE_IO)
 /*

lib/posix/options/CMakeLists.txt

@@ -67,6 +67,12 @@ if (NOT CONFIG_TC_PROVIDES_POSIX_FD_MGMT)
   )
 endif()
 
+if (NOT CONFIG_TC_PROVIDES_POSIX_FILE_LOCKING)
+  zephyr_library_sources_ifdef(CONFIG_POSIX_FILE_LOCKING
+    file_locking.c
+  )
+endif()
+
 if (NOT CONFIG_TC_PROVIDES_POSIX_FILE_SYSTEM)
   zephyr_library_sources_ifdef(CONFIG_POSIX_FILE_SYSTEM fs.c)
 endif()

lib/posix/options/Kconfig

@@ -14,6 +14,7 @@ rsource "Kconfig.c_lang_r"
 rsource "Kconfig.c_lib_ext"
 rsource "Kconfig.device_io"
 rsource "Kconfig.fd_mgmt"
+rsource "Kconfig.file_locking"
 rsource "Kconfig.file_system_r"
 rsource "Kconfig.fs"
 rsource "Kconfig.mem"

lib/posix/options/Kconfig.file_locking

@@ -0,0 +1,14 @@
+# Copyright (c) 2024 Tenstorrent AI ULC
+#
+# SPDX-License-Identifier: Apache-2.0
+
+config POSIX_FILE_LOCKING
+	bool "POSIX file locking"
+	help
+	  Select 'y' here and the following functions will be available:
+
+	  flockfile(), ftrylockfile(), funlockfile(), getc_unlocked(), getchar_unlocked(),
+	  putc_unlocked(), putchar_unlocked().
+
+	  For more information, please see
+	  https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_subprofiles.html

lib/posix/options/file_locking.c

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2024 Tenstorrent AI ULC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <errno.h>
+#include <stdio.h>
+
+#include <zephyr/toolchain.h>
+#include <zephyr/sys/fdtable.h>
+
+int zvfs_lock_file(FILE *file, k_timeout_t timeout);
+int zvfs_unlock_file(FILE *file);
+int zvfs_getc_unlocked(FILE *stream);
+int zvfs_putc_unlocked(int c, FILE *stream);
+
+/*
+ * This is incorrectly declared by (at least) newlib to be a macro with 2 arguments
+ * but it only takes 1 argument.
+ *
+ * Undefine any possible macro before attempting to define a duplicately-named function.
+ */
+#undef putchar_unlocked
+
+/*
+ * This is incorrectly declared by (at least) newlib to be a macro with 0 arguments
+ * but it should take 1 argument.
+ *
+ * Undefine any possible macro before attempting to define a duplicately-named function.
+ */
+#undef getchar_unlocked
+
+void flockfile(FILE *file)
+{
+	while (zvfs_lock_file(file, K_FOREVER) != 0) {
+		k_yield();
+	}
+}
+
+int ftrylockfile(FILE *file)
+{
+	return zvfs_lock_file(file, K_NO_WAIT);
+}
+
+void funlockfile(FILE *file)
+{
+	(void)zvfs_unlock_file(file);
+}
+
+int getc_unlocked(FILE *stream)
+{
+	return zvfs_getc_unlocked(stream);
+}
+
+int getchar_unlocked(void)
+{
+	return zvfs_getc_unlocked(stdin);
+}
+
+int putc_unlocked(int c, FILE *stream)
+{
+	return zvfs_putc_unlocked(c, stream);
+}
+
+int putchar_unlocked(int c)
+{
+	return zvfs_putc_unlocked(c, stdout);
+}