libc: io: implement file io buffering and internal locking for concurrency

lib/libc/io/stdio/file.h

@@ -1,25 +1,38 @@
 #ifndef _LIBC_IO_FILE_H_
 #define _LIBC_IO_FILE_H_
 
+#include "ringbuf.h"
+
+#include <mango/types.h>
 #include <stddef.h>
 
 enum file_flags {
 	FILE_EOF = 0x01u,
 	FILE_ERR = 0x02u,
 	FILE_BIN = 0x04u,
+	FILE_STATIC = 0x08u,
 };
 
 struct __opaque_file {
 	enum file_flags f_flags;
+	kern_futex_t f_lock;
+	int f_prev;
+	int f_buffer_mode;
 	int f_fd;
 	char f_unget;
-	char *f_buf;
-	size_t f_buf_datalen, f_buf_max;
-	size_t f_buf_readptr;
+	/* the current seek position of the buffered data (i.e. the offset of
+	 * the data that would be returned by reading f_buf). */
+	size_t f_seek;
+	struct ringbuf f_buf;
 };
 
-extern int __libc_file_refill(struct __opaque_file *f);
-extern int __libc_file_read(struct __opaque_file *f, void *out, size_t count);
-extern size_t __libc_file_available(struct __opaque_file *f);
+extern void __libc_file_lock(struct __opaque_file *f);
+extern void __libc_file_unlock(struct __opaque_file *f);
+
+extern long __libc_file_read(struct __opaque_file *f, void *p, size_t count);
+extern long __libc_file_write(
+	struct __opaque_file *f,
+	const void *p,
+	size_t count);
 
 #endif