Add write() hypercall

defs.h

@@ -4,6 +4,7 @@
 #define PORT_DISPLAY     0xEC
 #define PORT_OPEN        0xED
 #define PORT_READ        0xEE
+#define PORT_WRITE       0xEF
 
 #define MAX_FD 256
 

guest.c

@@ -39,18 +39,30 @@ int read(int fd, void *buf, size_t count) {
 	args[0].buf = buf;
 	args[0].count = count;
 
-	uint32_t temp = (char *)args - (char *)0; // Cast struct read_args * to uint32_t
+	uint32_t temp = (char *)args - (char *)0; // Cast struct rw_args * to uint32_t
 	outb(PORT_READ, temp);
 	temp = inb(PORT_READ);
 	return temp;
 }
 
+int write(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 rw_args * to uint32_t
+	outb(PORT_WRITE, temp);
+	temp = inb(PORT_WRITE);
+	return temp;
+}
+
 void
 __attribute__((noreturn))
 __attribute__((section(".start")))
 _start(void) {
 	const char *p;
-	int fd, fd1, fd2, fd3;
+	int fd, fd1, fd2, fd3, fd4;
 
 	/* Print Hello world */
 	display("----------------------------------------\n");
@@ -92,8 +104,7 @@ _start(void) {
 	display("\nContents of test.txt:\n");
 	display(buf);
 
-	// Clear buf
-	for(int i = 0; i < 100; i++) buf[i] = 0;
+	for(int i = 0; i < 100; i++) buf[i] = 0; // Clear buf
 
 	/* Test multiple opening & reading */
 	display("----------------------------------------\n");
@@ -126,7 +137,17 @@ _start(void) {
 
 	/* Test write() */
 	display("----------------------------------------\n");
+	display("Writing to test.txt - write returned ");
+	printVal(write(fd, "Writing someting\n", 17));
+	display("\n");
 
+	display("Contents of test.txt:\n");
+	// Reopen test.txt
+	open("test.txt");
+	fd4 = open("test.txt");
+	read(fd4, buf, sizeof(buf));
+	display(buf);
+	for(int i = 0; i < 100; i++) buf[i] = 0;
 
 	/* Halt after setting 0x400 & rax as 42 */
 	*(long *) 0x400 = 42;

kvm-hello-world.c

@@ -189,7 +189,7 @@ void handle_open(struct vm *vm, struct vcpu *vcpu) {
 
 		// Fetch filename from guest & open the file
 		filename = vm->mem + (uint64_t)*((char **)p);
-		fd = files[min_fd].fd = open(filename, O_RDONLY);
+		fd = files[min_fd].fd = open(filename, O_RDWR);
 		files[min_fd].in_use = 1;
 	}
 	else if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_IN) {
@@ -224,7 +224,6 @@ void handle_read(struct vm *vm, struct vcpu *vcpu) {
 		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) {
@@ -234,6 +233,40 @@ void handle_read(struct vm *vm, struct vcpu *vcpu) {
 	}
 }
 
+void handle_write(struct vm *vm, struct vcpu *vcpu) {
+	static int ret = 0;
+	if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_OUT) {
+		// Fetch arguments from guest
+		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 = write(fd, buf, count);
+	}
+	else if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_IN) {
+		// Return the number of bytes written to the guest
+		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;
@@ -283,6 +316,10 @@ int run_vm(struct vm *vm, struct vcpu *vcpu, size_t sz)
 				handle_read(vm, vcpu);
 				break;
 
+			case PORT_WRITE:
+				handle_write(vm, vcpu);
+				break;
+
 			default:
 				fprintf(stderr, "Unvalid hypercall\n");
 				exit(1);

test.txt

@@ -1 +1,2 @@
 Test file for open, read, and write
+Writing someting