Re: [RFC][PATCH 0/2] Monitoring unmounted fs with fanotify

[Christian Brauner <brauner@kernel.org>]

On Fri, Apr 14, 2023 at 09:29:01PM +0300, Amir Goldstein wrote:
> Jan,
> 
> Followup on my quest to close the gap with inotify functionality,
> here is a proposal for FAN_UNMOUNT event.
> 
> I have had many design questions about this:

I'm going to humbly express what I feel makes sense to me when looking
at this from a user perspective:

> 1) Should we also report FAN_UNMOUNT for marked inodes and sb
>    on sb shutdown (same as IN_UNMOUNT)?

My preference would be if this would be a separate event type.
FAN_SB_SHUTDOWN or something.

> 2) Should we also report FAN_UNMOUNT on sb mark for any unmounts
>    of that sb?

I don't think so. It feels to me that if you watch an sb you don't
necessarily want to watch bind mounts of that sb.

> 3) Should we report also the fid of the mount root? and if we do...
> 4) Should we report/consider FAN_ONDIR filter?
> 
> All of the questions above I answered "not unless somebody requests"
> in this first RFC.

Fwiw, I agree.

> 
> Specifically, I did get a request for an unmount event for containers
> use case.
> 
> I have also had doubts regarding the info records.
> I decided that reporting fsid and mntid is minimum, but couldn't
> decide if they were better of in a single MNTID record or seprate
> records.
> 
> I went with separate records, because:
> a) FAN_FS_ERROR has set a precendent of separate fid record with
>    fsid and empty fid, so I followed this precendent
> b) MNTID record we may want to add later with FAN_REPORT_MNTID
>    to all the path events, so better that it is independent

I agree.

> 
> There is test for the proposed API extention [1].
> 
> Thoughts?

I think this is a rather useful extension!