lib: posix: fs: add ftruncate support

Add support for ftruncate in posix implementation

Signed-off-by: Karthikeyan Krishnasamy <karthikeyan@linumiz.com>

include/zephyr/posix/unistd.h

@@ -238,6 +238,7 @@ ssize_t write(int file, const void *buffer, size_t count);
 ssize_t read(int file, void *buffer, size_t count);
 off_t lseek(int file, off_t offset, int whence);
 int fsync(int fd);
+int ftruncate(int fd, off_t length);
 
 /* File System related operations */
 int rename(const char *old, const char *newp);

lib/posix/options/fs.c

@@ -416,3 +416,18 @@ int mkdir(const char *path, mode_t mode)
 
 	return 0;
 }
+
+/**
+ * @brief Truncate file to specified length.
+ *
+ */
+int ftruncate(int fd, off_t length)
+{
+	struct posix_fs_desc *ptr = NULL;
+
+	ptr = z_get_fd_obj(fd, NULL, EBADF);
+	if (!ptr)
+		return -1;
+
+	return fs_truncate(&ptr->file, length);
+}