linux-kernel - Re: [RFC][PATCH] Cross Memory Attach

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Date:	Wed, 15 Sep 2010 08:11:16 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christopher Yeoh <cyeoh@....ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Cross Memory Attach

On Tue, Sep 14, 2010 at 6:18 PM, Christopher Yeoh <cyeoh@....ibm.com> wrote:
> +
> +               if (copy_to) {
> +                       ret = copy_from_user(target_kaddr,
> +                                            user_buf + *bytes_copied,
> +                                            bytes_to_copy);
> +                       if (ret) {
> +                               kunmap(process_pages[i]);
> +                               goto end;
> +                       }
> +               } else {
> +                       ret = copy_to_user(user_buf + *bytes_copied,
> +                                          target_kaddr, bytes_to_copy);
> +                       if (ret) {
> +                               kunmap(process_pages[i]);
> +                               goto end;
> +                       }
> +               }
> +               kunmap(process_pages[i]);

Btw, please just do this as

   if (copy_to)
      ret = copy_from_user(..);
   else
      ret = copy_to_user(..);
   kunmap(process_pages[i]);
   if (ret)
      goto out;

(and also, I think you should probably use a real variable for
*bytes_copied, rather than update things behind the pointer. Update
the pointer just once at the end instead, or preferably just change
the calling convention to just return the number of bytes copied, and
let the caller do the page counting).

                      Linus
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