Re: [PATCH v2] Cygwin: clipboard: Fix a bug in read().

[Mark Geisert <mark@maxrnd.com>]

Takashi Yano wrote:
[...]
> I think the following patch makes the intent clearer.
> What do you think?
> 
> 
>  From d0aee9af225384a24ac6301f987ce2e94f262500 Mon Sep 17 00:00:00 2001
> From: Takashi Yano <takashi.yano@nifty.ne.jp>
> Date: Wed, 8 Dec 2021 17:06:03 +0900
> Subject: [PATCH] Cygwin: clipboard: Make intent of the code clearer.
> 
> ---
>   winsup/cygwin/fhandler_clipboard.cc   | 4 ++--
>   winsup/cygwin/include/sys/clipboard.h | 1 +
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/winsup/cygwin/fhandler_clipboard.cc b/winsup/cygwin/fhandler_clipboard.cc
> index 05f54ffb3..65a3cad97 100644
> --- a/winsup/cygwin/fhandler_clipboard.cc
> +++ b/winsup/cygwin/fhandler_clipboard.cc
> @@ -76,7 +76,7 @@ fhandler_dev_clipboard::set_clipboard (const void *buf, size_t len)
>         clipbuf->cb_sec  = clipbuf->ts.tv_sec;
>   #endif
>         clipbuf->cb_size = len;
> -      memcpy (&clipbuf[1], buf, len); // append user-supplied data
> +      memcpy (clipbuf->data, buf, len); // append user-supplied data
>   
>         GlobalUnlock (hmem);
>         EmptyClipboard ();
> @@ -229,7 +229,7 @@ fhandler_dev_clipboard::read (void *ptr, size_t& len)
>         if (pos < (off_t) clipbuf->cb_size)
>   	{
>   	  ret = (len > (clipbuf->cb_size - pos)) ? clipbuf->cb_size - pos : len;
> -	  memcpy (ptr, (char *) (clipbuf + 1) + pos, ret);
> +	  memcpy (ptr, clipbuf->data + pos, ret);
>   	  pos += ret;
>   	}
>       }
> diff --git a/winsup/cygwin/include/sys/clipboard.h b/winsup/cygwin/include/sys/clipboard.h
> index 4c00c8ea1..b2544be85 100644
> --- a/winsup/cygwin/include/sys/clipboard.h
> +++ b/winsup/cygwin/include/sys/clipboard.h
> @@ -44,6 +44,7 @@ typedef struct
>       };
>     };
>     uint64_t      cb_size; // 8 bytes everywhere
> +  char          data[];
>   } cygcb_t;
>   
>   #endif

Sigh.  I guess it's not possible to keep rid of a data item like I'd hoped.  At 
least "data[]" is cleaner than the historical "data[1]" here.  If you call the 
item cb_data I can live with it.
Thanks all for the discussion.

..mark