linux-ext4 - Re: [PATCH v6 09/21] fsnotify: Allow events reported with an empty inode

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Date:   Fri, 13 Aug 2021 10:58:56 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, Linux API <linux-api@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Theodore Tso <tytso@....edu>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com
Subject: Re: [PATCH v6 09/21] fsnotify: Allow events reported with an empty inode

On Fri, Aug 13, 2021 at 12:41 AM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Some file system events (i.e. FS_ERROR) might not be associated with an
> inode.  For these, it makes sense to associate them directly with the
> super block of the file system they apply to.  This patch allows the
> event to be reported with a NULL inode, by recovering the superblock
> directly from the data field, if needed.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>
> --
> Changes since v5:
>   - add fsnotify_data_sb handle to retrieve sb from the data field. (jan)
> ---
>  fs/notify/fsnotify.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index 30d422b8c0fc..536db02cb26e 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -98,6 +98,14 @@ void fsnotify_sb_delete(struct super_block *sb)
>         fsnotify_clear_marks_by_sb(sb);
>  }
>
> +static struct super_block *fsnotify_data_sb(const void *data, int data_type)
> +{
> +       struct inode *inode = fsnotify_data_inode(data, data_type);
> +       struct super_block *sb = inode ? inode->i_sb : NULL;
> +
> +       return sb;
> +}
> +
>  /*
>   * Given an inode, first check if we care what happens to our children.  Inotify
>   * and dnotify both tell their parents about events.  If we care about any event
> @@ -455,8 +463,10 @@ static void fsnotify_iter_next(struct fsnotify_iter_info *iter_info)
>   *             @file_name is relative to
>   * @file_name: optional file name associated with event
>   * @inode:     optional inode associated with event -
> - *             either @dir or @inode must be non-NULL.
> - *             if both are non-NULL event may be reported to both.
> + *             If @dir and @inode are NULL, @data must have a type that
> + *             allows retrieving the file system associated with this

Irrelevant comment. sb must always be available from @data.

> + *             event.  if both are non-NULL event may be reported to
> + *             both.
>   * @cookie:    inotify rename cookie
>   */
>  int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
> @@ -483,7 +493,7 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
>                  */
>                 parent = dir;
>         }
> -       sb = inode->i_sb;
> +       sb = inode ? inode->i_sb : fsnotify_data_sb(data, data_type);

        const struct path *path = fsnotify_data_path(data, data_type);
+       const struct super_block *sb = fsnotify_data_sb(data, data_type);

All the games with @data @inode and @dir args are irrelevant to this.
sb should always be available from @data and it does not matter
if fsnotify_data_inode() is the same as @inode, @dir or neither.
All those inodes are anyway on the same sb.

Thanks,
Amir.