tty: hvc_console: use flexible array for outbuf

This means:
* move outbuf to the end of struct hvc_struct and convert from pointer
  to flexible array (the structure is smaller now)
* use struct_size() at the allocation site
* align outbuf in the struct instead of ALIGN() at kzalloc()

And apart from the above, use u8 instead of char (which are the same
thanks to -funsigned-char). The former is now preferred over the latter.

It makes the code easier to understand.
Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20231121092258.9334-12-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/hvc/hvc_console.c

@@ -922,8 +922,7 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
 			return ERR_PTR(err);
 	}
 
-	hp = kzalloc(ALIGN(sizeof(*hp), sizeof(long)) + outbuf_size,
-			GFP_KERNEL);
+	hp = kzalloc(struct_size(hp, outbuf, outbuf_size), GFP_KERNEL);
 	if (!hp)
 		return ERR_PTR(-ENOMEM);
 
@@ -931,7 +930,6 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
 	hp->data = data;
 	hp->ops = ops;
 	hp->outbuf_size = outbuf_size;
-	hp->outbuf = &((char *)hp)[ALIGN(sizeof(*hp), sizeof(long))];
 
 	tty_port_init(&hp->port);
 	hp->port.ops = &hvc_port_ops;

drivers/tty/hvc/hvc_console.h

@@ -37,7 +37,6 @@ struct hvc_struct {
 	spinlock_t lock;
 	int index;
 	int do_wakeup;
-	char *outbuf;
 	int outbuf_size;
 	int n_outbuf;
 	uint32_t vtermno;
@@ -48,6 +47,7 @@ struct hvc_struct {
 	struct work_struct tty_resize;
 	struct list_head next;
 	unsigned long flags;
+	u8 outbuf[] __aligned(sizeof(long));
 };
 
 /* implemented by a low level driver */