linux-ext4 - Re: [PATCH v7 10/28] fsnotify: Retrieve super block from the data field

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Date:   Fri, 15 Oct 2021 08:39:39 +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>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v7 10/28] fsnotify: Retrieve super block from the data field

On Fri, Oct 15, 2021 at 12:38 AM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Some file system events (i.e. FS_ERROR) might not be associated with an
> inode or directory.  For these, we can retrieve the super block from the
> data field.  But, since the super_block is available in the data field
> on every event type, simplify the code to always retrieve it from there,
> through a new helper.
>
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
Reviewed-by: Amir Goldstein <amir73il@...il.com>

>
> --
> Changes since v6:
>   - Always use data field for superblock retrieval
> Changes since v5:
>   - add fsnotify_data_sb handle to retrieve sb from the data field. (jan)
> ---
>  fs/notify/fsnotify.c             |  7 +++----
>  include/linux/fsnotify_backend.h | 15 +++++++++++++++
>  2 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index 963e6ce75b96..fde3a1115a17 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -455,16 +455,16 @@ 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 both 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,
>              const struct qstr *file_name, struct inode *inode, u32 cookie)
>  {
>         const struct path *path = fsnotify_data_path(data, data_type);
> +       struct super_block *sb = fsnotify_data_sb(data, data_type);
>         struct fsnotify_iter_info iter_info = {};
> -       struct super_block *sb;
>         struct mount *mnt = NULL;
>         struct inode *parent = NULL;
>         int ret = 0;
> @@ -483,7 +483,6 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
>                  */
>                 parent = dir;
>         }
> -       sb = inode->i_sb;
>
>         /*
>          * Optimization: srcu_read_lock() has a memory barrier which can
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index b323d0c4b967..035438fe4a43 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -289,6 +289,21 @@ static inline const struct path *fsnotify_data_path(const void *data,
>         }
>  }
>
> +static inline struct super_block *fsnotify_data_sb(const void *data,
> +                                                  int data_type)
> +{
> +       switch (data_type) {
> +       case FSNOTIFY_EVENT_INODE:
> +               return ((struct inode *)data)->i_sb;
> +       case FSNOTIFY_EVENT_DENTRY:
> +               return ((struct dentry *)data)->d_sb;
> +       case FSNOTIFY_EVENT_PATH:
> +               return ((const struct path *)data)->dentry->d_sb;
> +       default:
> +               return NULL;
> +       }
> +}
> +
>  enum fsnotify_obj_type {
>         FSNOTIFY_OBJ_TYPE_INODE,
>         FSNOTIFY_OBJ_TYPE_PARENT,
> --
> 2.33.0
>