linux-ext4 - Re: [PATCH v9 24/31] fanotify: Report fid entry even for zero-length file

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Date:   Tue, 26 Oct 2021 12:09:19 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        Dave Chinner <david@...morbit.com>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>, kernel@...labora.com,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v9 24/31] fanotify: Report fid entry even for zero-length file_handle

On Mon, Oct 25, 2021 at 10:30 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Non-inode errors will reported with an empty file_handle.  In
> preparation for that, allow some events to print the FID record even if
> there isn't any file_handle encoded
>
> Even though FILEID_ROOT is used internally, make zero-length file
> handles be reported as FILEID_INVALID.
>
> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>
> ---
> Changes since v8:
>   - Move fanotify_event_has_object_fh check here (jan)

Logically, this move is wrong, because after this patch,
copy_fid_info_to_user() can theoretically be called with NULL fh in the
existing construct of:
  if (fanotify_event_has_object_fh(event)) {
  ...
    ret = copy_fid_info_to_user(fanotify_event_fsid(event),

fanotify_event_object_fh(event),

The thing that prevents this case in effect is that FAN_FS_ERROR
is not yet wired, but I am not sure if leaving this theoretic bisect
issue is a good idea.

Anyway, that's a very minor theoretic issue and I am sure Jan can
decide whether to deal with it and how (no need to post v10 IMO).

Thanks,
Amir.