linux-kernel - Re: fs/notify/fanotify/fanotify_user.c:370:3: warning: Assignment of function parameter has no effect outside the function. Did you forget dereferencing

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Message-ID: <CAOQ4uxh9s8ukzyUvADZzF-kyTGXgZxdei9LyfzEDHJ_h+wKRFg@mail.gmail.com>
Date:   Wed, 5 Aug 2020 19:58:57 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>
Subject: Re: fs/notify/fanotify/fanotify_user.c:370:3: warning: Assignment of
 function parameter has no effect outside the function. Did you forget dereferencing

On Wed, Aug 5, 2020 at 10:40 AM kernel test robot <lkp@...el.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   4da9f3302615f4191814f826054846bf843e24fa
> commit: 44d705b0370b1d581f46ff23e5d33e8b5ff8ec58 fanotify: report name info for FAN_DIR_MODIFY event
> date:   4 months ago

Gee that's an old patch...

> compiler: nds32le-linux-gcc (GCC) 9.3.0
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
>
>
> cppcheck warnings: (new ones prefixed by >>)
>
> >> fs/notify/fanotify/fanotify_user.c:370:3: warning: Assignment of function parameter has no effect outside the function. Did you forget dereferencing it? [uselessAssignmentPtrArg]
>      buf += ret;
>      ^
> >> fs/notify/fanotify/fanotify_user.c:371:3: warning: Assignment of function parameter has no effect outside the function. [uselessAssignmentArg]
>      count -= ret;
>      ^
...

>    348          /* Event info records order is: dir fid + name, child fid */
>    349          if (fanotify_event_name_len(event)) {
>    350                  struct fanotify_name_event *fne = FANOTIFY_NE(event);
>    351
>    352                  ret = copy_info_to_user(fanotify_event_fsid(event),
>    353                                          fanotify_event_dir_fh(event),
>    354                                          fne->name, fne->name_len,
>    355                                          buf, count);
>    356                  if (ret < 0)
>    357                          return ret;
>    358
>    359                  buf += ret;
>    360                  count -= ret;
>    361          }
>    362
>    363          if (fanotify_event_object_fh_len(event)) {
>    364                  ret = copy_info_to_user(fanotify_event_fsid(event),
>    365                                          fanotify_event_object_fh(event),
>    366                                          NULL, 0, buf, count);
>    367                  if (ret < 0)
>    368                          return ret;
>    369
>  > 370                  buf += ret;
>  > 371                  count -= ret;
>    372          }

This is intentional.
The code is more readable and robust this way even though these
assignments have no effect in current code.

Thanks,
Amir.