posix: fd_mgmt: implement dup(), dup2(), fseeko(), and ftello()

Implement the remaining functions from the POSIX_FD_MGMT Option
Group that are part of POSIX, and add the
CONFIG_REQUIRES_FULL_LIBC dependency to CONFIG_POSIX_FD_MGMT, to
pull in the remaining C89 functions.

The POSIX_FD_MGMT Option Group is required for PSE52, PSE53, and
PSE54 Subprofiling Option Groups.

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

lib/os/fdtable.c

@@ -424,6 +424,46 @@ int zvfs_fileno(FILE *file)
 	return (struct fd_entry *)file - fdtable;
 }
 
+int zvfs_dup(int fd, int *newfd)
+{
+	int ret;
+
+	if (_check_fd(fd) < 0) {
+		return -1;
+	}
+
+	(void)k_mutex_lock(&fdtable_lock, K_FOREVER);
+
+	if (newfd == NULL) {
+		/* dup() - just find lowest-numbered fd */
+		ret = _find_fd_entry();
+	} else {
+		/* dup2() - check if newfd is valid */
+		if (_check_fd(*newfd) < 0) {
+			ret = -1;
+		} else {
+			if (fdtable[fd].vtable->close) {
+				(void)fdtable[fd].vtable->close(fdtable[fd].obj);
+			}
+			ret = *newfd;
+		}
+	}
+
+	if (ret >= 0) {
+		/* Mark entry as used and initialize fields */
+		if (newfd == NULL) {
+			(void)z_fd_ref(ret);
+		}
+		fdtable[ret] = fdtable[fd];
+		k_mutex_init(&fdtable[ret].lock);
+		k_condvar_init(&fdtable[ret].cond);
+	}
+
+	k_mutex_unlock(&fdtable_lock);
+
+	return ret;
+}
+
 int zvfs_fstat(int fd, struct stat *buf)
 {
 	if (_check_fd(fd) < 0) {

lib/posix/options/Kconfig.fd_mgmt

@@ -5,6 +5,8 @@
 menuconfig POSIX_FD_MGMT
 	bool "POSIX file descriptor management [EXPERIMENTAL]"
 	select EXPERIMENTAL
+	select FDTABLE
+	select REQUIRES_FULL_LIBC
 	help
 	  Select 'y' here and Zephyr will provide implementations for the POSIX_FD_MGMT Option Group.
 	  This includes support for dup(), dup2(), fcntl(), fseeko(), ftello(), ftruncate(),

lib/posix/options/fd_mgmt.c

@@ -7,17 +7,30 @@
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <stdio.h>
 
 #include <zephyr/posix/unistd.h>
 #include <zephyr/posix/sys/select.h>
 #include <zephyr/posix/sys/socket.h>
 #include <zephyr/sys/fdtable.h>
 
 /* prototypes for external, not-yet-public, functions in fdtable.c or fs.c */
+int zvfs_dup(int fd, int *newfd);
 int zvfs_fcntl(int fd, int cmd, va_list arg);
+int zvfs_fileno(FILE *file);
 int zvfs_ftruncate(int fd, off_t length);
 off_t zvfs_lseek(int fd, off_t offset, int whence);
 
+int dup(int fd)
+{
+	return zvfs_dup(fd, NULL);
+}
+
+int dup2(int oldfd, int newfd)
+{
+	return zvfs_dup(oldfd, &newfd);
+}
+
 int fcntl(int fd, int cmd, ...)
 {
 	int ret;
@@ -33,6 +46,30 @@ int fcntl(int fd, int cmd, ...)
 FUNC_ALIAS(fcntl, _fcntl, int);
 #endif /* CONFIG_POSIX_FD_MGMT_ALIAS_FCNTL */
 
+int fseeko(FILE *file, off_t offset, int whence)
+{
+	int fd;
+
+	fd = zvfs_fileno(file);
+	if (fd < 0) {
+		return -1;
+	}
+
+	return zvfs_lseek(fd, offset, whence);
+}
+
+off_t ftello(FILE *file)
+{
+	int fd;
+
+	fd = zvfs_fileno(file);
+	if (fd < 0) {
+		return -1;
+	}
+
+	return zvfs_lseek(fd, 0, SEEK_CUR);
+}
+
 int ftruncate(int fd, off_t length)
 {
 	return zvfs_ftruncate(fd, length);