Re: [PATCH v5 10/18] fs: add a flag to indicate the fs supports pre-content events

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Sep 4, 2024 at 10:29 PM Josef Bacik <josef@toxicpanda.com> wrote:
>
> The pre-content events require some extra thinking, especially around
> page faults.  In order to make sure we don't advertise a feature working
> that doesn't actually work, add a flag to allow file systems to opt-in
> to this behavior.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Better squash this patch to FAN_PRE_ACCESS patch, so it will
not be allowed to mark with FAN_PRE_ACCESS on unsupported fs
mid series.

OR - move this patch before the FAN_PRE_ACCESS patch and pre-define
FANOTIFY_PRE_CONTENT_EVENTS to 0.

Apart from that, you may add:

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.

> ---
>  fs/notify/fanotify/fanotify_user.c | 2 ++
>  include/linux/fs.h                 | 1 +
>  include/linux/fsnotify.h           | 4 ++++
>  3 files changed, 7 insertions(+)
>
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 53eee8af34a0..936e9f9e0cbc 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -1736,6 +1736,8 @@ static int fanotify_events_supported(struct fsnotify_group *group,
>
>         /* Pre-content events are only supported on regular files and dirs */
>         if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {
> +               if (!(path->mnt->mnt_sb->s_type->fs_flags & FS_ALLOW_HSM))
> +                       return -EINVAL;
>                 if (!is_dir && !d_is_reg(path->dentry))
>                         return -EINVAL;
>                 if (is_dir && mask & FAN_PRE_MODIFY)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index fd34b5755c0b..5708e91d3625 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2494,6 +2494,7 @@ struct file_system_type {
>  #define FS_USERNS_MOUNT                8       /* Can be mounted by userns root */
>  #define FS_DISALLOW_NOTIFY_PERM        16      /* Disable fanotify permission events */
>  #define FS_ALLOW_IDMAP         32      /* FS has been updated to handle vfs idmappings. */
> +#define FS_ALLOW_HSM           64      /* FS can handle fanotify pre-content events. */
>  #define FS_RENAME_DOES_D_MOVE  32768   /* FS will handle d_move() during rename() internally. */
>         int (*init_fs_context)(struct fs_context *);
>         const struct fs_parameter_spec *parameters;
> diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> index 9d001d328619..27992b548f0c 100644
> --- a/include/linux/fsnotify.h
> +++ b/include/linux/fsnotify.h
> @@ -179,6 +179,10 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
>         if (!S_ISDIR(inode->i_mode) && !S_ISREG(inode->i_mode))
>                 return 0;
>
> +       /* The fs doesn't support pre-content events. */
> +       if (!(inode->i_sb->s_type->fs_flags & FS_ALLOW_HSM))
> +               return 0;
> +
>         if (perm_mask & MAY_WRITE)
>                 fsnotify_mask = FS_PRE_MODIFY;
>         else if (perm_mask & (MAY_READ | MAY_ACCESS))
> --
> 2.43.0
>