fanotify and namespaces/bind mounts

fanotify and namespaces/bind mounts

[Marko Rauhamaa]

If I call fanotify_mark(... FAN_MARK_ADD | FAN_MARK_MOUNT ...), I get
notifications on all files on the file system.

Except I don't.

If a process has mounted directories on the file system in a different
namespace, the global namespace experiences file system events but no
fanotify events are generated. A similar limitation applies to bind
mounts.

You can easily see this behavior in action. Do "man fanotify", and copy
the example program to, say, example.c. Then,

    cc -o example example.c
    mkdir -p /mnt/xyz
    mount -o bind /root /mnt/xyz
    ./example /root

The last command prints out fanotify events. It will display events for

    touch /root/xyzzy

but nothing for

    touch /mnt/xyz/zyxxy

or

    unshare -m touch /root/yxyyx

Should the current situation be considered a bug in fanotify? Or is
there another recommended way to monitor file system events
categorigally?


Marko

Re: fanotify and namespaces/bind mounts

[riya khanna]

Are fsnotify events generated per mount namespace?

On Thu, Oct 29, 2015 at 9:29 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>
> If I call fanotify_mark(... FAN_MARK_ADD | FAN_MARK_MOUNT ...), I get
> notifications on all files on the file system.
>
> Except I don't.
>
> If a process has mounted directories on the file system in a different
> namespace, the global namespace experiences file system events but no
> fanotify events are generated. A similar limitation applies to bind
> mounts.
>
> You can easily see this behavior in action. Do "man fanotify", and copy
> the example program to, say, example.c. Then,
>
>     cc -o example example.c
>     mkdir -p /mnt/xyz
>     mount -o bind /root /mnt/xyz
>     ./example /root
>
> The last command prints out fanotify events. It will display events for
>
>     touch /root/xyzzy
>
> but nothing for
>
>     touch /mnt/xyz/zyxxy
>
> or
>
>     unshare -m touch /root/yxyyx
>
> Should the current situation be considered a bug in fanotify? Or is
> there another recommended way to monitor file system events
> categorigally?
>
>
> Marko
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