lib: xpc: implement scatter/gather i/o for buffers and messages

lib/libxpc/buffer.c

@@ -5,6 +5,7 @@
 
 kern_status_t xpc_buffer_read(
 	const xpc_buffer_t *buf,
+	size_t offset,
 	void *out,
 	size_t max,
 	size_t *nr_read)
@@ -14,25 +15,35 @@ kern_status_t xpc_buffer_read(
 		return KERN_BAD_STATE;
 	}
 
-	size_t to_read = max;
-	if (to_read > buf->buf_len) {
-		to_read = buf->buf_len;
+	if (offset >= buf->buf_len) {
+		if (nr_read) {
+			*nr_read = 0;
+		}
+
+		return KERN_OK;
 	}
 
-	kern_status_t status
-		= xpc_msg_read(buf->buf_origin, buf->buf_offset, out, to_read);
+	size_t to_read = max;
+	if (offset + to_read > buf->buf_len) {
+		to_read = buf->buf_len - offset;
+	}
+
+	kern_status_t status = xpc_msg_read(
+		buf->buf_origin,
+		buf->buf_offset + offset,
+		out,
+		to_read,
+		nr_read);
 	if (status != KERN_OK) {
 		return status;
 	}
 
-	/* TODO */
-	*nr_read = to_read;
-
 	return KERN_OK;
 }
 
 kern_status_t xpc_buffer_write(
 	xpc_buffer_t *buf,
+	size_t offset,
 	const void *in,
 	size_t len,
 	size_t *nr_written)
@@ -41,9 +52,17 @@ kern_status_t xpc_buffer_write(
 		return KERN_BAD_STATE;
 	}
 
+	if (offset >= buf->buf_max) {
+		if (nr_written) {
+			*nr_written = 0;
+		}
+
+		return KERN_OK;
+	}
+
 	size_t to_write = len;
-	if (to_write > buf->buf_max) {
-		to_write = buf->buf_max;
+	if (offset + to_write > buf->buf_max) {
+		to_write = buf->buf_max - offset;
 	}
 
 	if (!(buf->buf_flags & XPC_BUFFER_F_REMOTE)) {
@@ -54,8 +73,70 @@ kern_status_t xpc_buffer_write(
 
 	return xpc_msg_write(
 		buf->buf_origin,
-		buf->buf_offset,
+		buf->buf_offset + offset,
 		in,
 		to_write,
 		nr_written);
 }
+
+xpc_status_t xpc_buffer_readv(
+	const xpc_buffer_t *buf,
+	size_t offset,
+	kern_iovec_t *iov,
+	size_t nr_iov,
+	size_t *nr_read)
+{
+	if (!(buf->buf_flags & XPC_BUFFER_F_IN)) {
+		return KERN_BAD_STATE;
+	}
+
+	/* TODO limit to buffer bounds */
+
+	if (!(buf->buf_flags & XPC_BUFFER_F_REMOTE)) {
+		/* TODO */
+		return KERN_UNIMPLEMENTED;
+	}
+
+	return xpc_msg_readv(
+		buf->buf_origin,
+		buf->buf_offset + offset,
+		iov,
+		nr_iov,
+		nr_read);
+}
+
+xpc_status_t xpc_buffer_writev(
+	xpc_buffer_t *buf,
+	size_t offset,
+	kern_iovec_t *iov,
+	size_t nr_iov,
+	size_t *nr_written)
+{
+	if (!(buf->buf_flags & XPC_BUFFER_F_OUT)) {
+		return KERN_BAD_STATE;
+	}
+
+	/* TODO limit to buffer bounds */
+
+	if (!(buf->buf_flags & XPC_BUFFER_F_REMOTE)) {
+		/* TODO */
+		return KERN_UNIMPLEMENTED;
+	}
+
+	return xpc_msg_writev(
+		buf->buf_origin,
+		buf->buf_offset + offset,
+		iov,
+		nr_iov,
+		nr_written);
+}
+
+xpc_status_t xpc_buffer_length(const xpc_buffer_t *s)
+{
+	return s->buf_len;
+}
+
+xpc_status_t xpc_buffer_capacity(const xpc_buffer_t *s)
+{
+	return s->buf_max;
+}