From cb1f903fe81c2c9ca971534696836e21486dfafc Mon Sep 17 00:00:00 2001
From: Joshua Saxby <joshua.a.saxby@gmail.com>
Date: Wed, 4 Dec 2019 14:42:04 +0000
Subject: [PATCH] Implemented read() Tested this at least works on the console
by running the shell program it works
---
userprog/syscall_read.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/userprog/syscall_read.c b/userprog/syscall_read.c
index bd6c2df..67f7d98 100644
--- a/userprog/syscall_read.c
+++ b/userprog/syscall_read.c
@@ -3,10 +3,40 @@
*
* Authored by Joshua Saxby
*/
-#include "filesys/filesys.h"
+#include <stddef.h>
+#include "devices/input.h"
+#include "filesys/file.h"
#include "system_calls.h"
#include "threads/interrupt.h"
void syscall_read(struct intr_frame *f) {
- (void*)0;
+ // first argument is syscall code (already handled)
+ int fd = *((int*)f->esp + 1); // file descriptor is second argument
+ char* buffer = (void*)(*((int*)f->esp + 2)); // buffer is third argument
+ unsigned size = *((unsigned*)((int*)f->esp + 3)); // size to read is fourth
+ // reading from stdin (keyboard) is a special case
+ switch (fd) {
+ case 0: {
+ // read from keyboard for as many bytes as requested
+ for (size_t i = 0; i < size; i++) {
+ *(buffer + i) = input_getc();
+ }
+ f->eax = size;
+ break;
+ }
+ case 1: // stdout
+ case 2: // stderr
+ f->eax = -1; // it is a mistake to attempt to read from stdout or stderr
+ break;
+ default: {
+ // otherwise, we need to read from a file denoted by fd
+ struct file* file_to_read = get_associated_file_pointer(fd);
+ if (file_to_read == NULL) {
+ f->eax = -1; // invalid file descriptor
+ break;
+ }
+ f->eax = file_read(file_to_read, buffer, size);
+ break;
+ }
+ }
}
--
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