Implemented fio_read, fio_write, and fio_flush on Horizon

photon/libc/sys/horizon/fio.c

@@ -1,5 +1,6 @@
 #include <magenta/misc.h>
 #include <stdio.h>
+#include <unistd.h>
 #include "sys/types.h"
 #include "__fio.h"
 
@@ -55,12 +56,28 @@ int __fileno(struct __io_file *f)
 
 unsigned int __fio_read(struct __io_file *f, char *buf, unsigned int sz)
 {
+    ssize_t err = read(f->fd, buf, sz);
+    if (err < 0) {
+        f->err = 1;
         return 0;
+    }
+
+    return err;
 }
 
 unsigned int __fio_write(struct __io_file *f, const char *buf, unsigned int sz)
 {
-    mx_console_write(buf, sz);
+    for (unsigned int i = 0; i < sz; i++) {
+        if (f->buf_idx >= __FIO_BUFSZ) {
+            __fio_flush(f);
+        }
+
+        f->buf[f->buf_idx++] = buf[i];
+        if (buf[i] == '\n') {
+            __fio_flush(f);
+        }
+    }
+
     return sz;
 }
 
@@ -71,7 +88,14 @@ int __fio_ungetc(struct __io_file *f, char c)
 
 unsigned int __fio_flush(struct __io_file *f)
 {
-    return 0;
+    ssize_t res = write(f->fd, f->buf, f->buf_idx);
+    if (res != f->buf_idx) {
+        f->err = 1;
+    }
+
+    size_t flushed = f->buf_idx;
+    f->buf_idx = 0;
+    return flushed;
 }
 
 int __fio_error(struct __io_file *f)