Add read() hypercall

defs.h

@@ -3,5 +3,12 @@
 #define PORT_GETNUMEXITS 0xEB
 #define PORT_DISPLAY     0xEC
 #define PORT_OPEN        0xED
+#define PORT_READ        0xEE
 
-#define MAX_FD 256
+#define MAX_FD 256
+
+struct rw_args{
+	int fd;
+	void *buf;
+	size_t count;
+};

guest.c

@@ -33,6 +33,18 @@ int open(const char *filename) {
 	return temp;
 }
 
+int read(int fd, void *buf, size_t count) {
+	struct rw_args args[1];
+	args[0].fd = fd;
+	args[0].buf = buf;
+	args[0].count = count;
+
+	uint32_t temp = (char *)args - (char *)0; // Cast struct read_args * to uint32_t
+	outb(PORT_READ, temp);
+	temp = inb(PORT_READ);
+	return temp;
+}
+
 void
 __attribute__((noreturn))
 __attribute__((section(".start")))
@@ -41,30 +53,44 @@ _start(void) {
 	int fd;
 
 	/* Print Hello world */
+	display("----------------------------------------\n");
 	for (p = "Hello, world!\n"; *p; ++p)
 		outb(PORT_PRINT_CHAR, *p);
 
 	/* Test printVal() */
+	display("----------------------------------------\n");
 	printVal(1234);
 	outb(PORT_PRINT_CHAR, '\n');
 
 	/* Test getNumExits() */
+	display("----------------------------------------\n");
 	uint32_t numExits = getNumExits();
 	printVal(numExits);
 	outb(PORT_PRINT_CHAR, '\n');
 
 	/* Test display() */
+	display("----------------------------------------\n");
 	printVal(getNumExits());
 	display("\nHello world again!\n");
 	printVal(getNumExits());
 	display("\n");
 
 	/* Test open() */
+	display("----------------------------------------\n");
 	display("Opening test.txt\n");
 	fd = open("test.txt");
 	printVal(fd);
 	display("\n");
 
+	/* Test read() */
+	display("----------------------------------------\n");
+	char buf[100];
+	display("Reading test.txt - read returned ");
+	printVal(read(fd, buf, sizeof(buf)));
+
+	display("\nContents of test.txt:\n");
+	display(buf);
+
 	/* Halt after setting 0x400 & rax as 42 */
 	*(long *) 0x400 = 42;
 	for (;;)

kvm-hello-world.c

@@ -188,9 +188,8 @@ void handle_open(struct vm *vm, struct vcpu *vcpu) {
 
 		filename = vm->mem + (uint64_t)*((char **)p);
 
-		files[min_fd].fd = open(filename, O_RDONLY);
+		fd = files[min_fd].fd = open(filename, O_RDONLY);
 		files[min_fd].in_use = 1;
-		fd = files[min_fd].fd;
 
 		printf("opened %s as fd %d. min_fd is %d\n", filename, files[min_fd].fd, min_fd);
 	}
@@ -201,6 +200,39 @@ void handle_open(struct vm *vm, struct vcpu *vcpu) {
 	}
 }
 
+void handle_read(struct vm *vm, struct vcpu *vcpu) {
+	static int ret = 0;
+	if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_OUT) {
+		char *p = (char *)vcpu->kvm_run + vcpu->kvm_run->io.data_offset;
+		struct rw_args *args = (struct rw_args*)(vm->mem + (uint64_t)(*((char **)p)));
+
+		int fd = args->fd;
+		if(fd < 0 || fd >= MAX_FD) { // Invalid fd
+			ret = -1;
+			return;
+		}
+		for(int i = 0; i < MAX_FD; i++) {
+			if(files[i].fd == fd) {
+				if(!files[i].in_use) { // Unopened fd
+					ret = -1;
+					return;
+				}
+				break;
+			}
+		}
+
+		void *buf = vm->mem + (uint64_t)(args->buf);
+
+		size_t count = args->count;
+
+		ret = read(fd, buf, count);
+	}
+	else if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_IN) {
+		char *p = (char *)vcpu->kvm_run + vcpu->kvm_run->io.data_offset;
+		*((int32_t *)p) = ret;
+	}
+}
+
 int run_vm(struct vm *vm, struct vcpu *vcpu, size_t sz)
 {
 	struct kvm_regs regs;
@@ -246,6 +278,10 @@ int run_vm(struct vm *vm, struct vcpu *vcpu, size_t sz)
 				handle_open(vm, vcpu);
 				break;
 
+			case PORT_READ:
+				handle_read(vm, vcpu);
+				break;
+
 			default:
 				fprintf(stderr, "Unvalid hypercall\n");
 				exit(1);