[systemd-devel] Masking mount units

[Nils Kattenbeck]

On Tue, Nov 19, 2024 at 1:00 AM Lennart Poettering
<lennart at poettering.net> wrote:
>
> On Do, 14.11.24 14:25, Phillip Susi (phill at thesusis.net) wrote:
>
> > Lennart Poettering <lennart at poettering.net> writes:
> >
> > > the BLKFLSBUF ioctl() works fine on block device fds open for read only.
> >
> > Oh, I might have to change that to use a read only open then.
> >
> > > I am not following anymore. As *long* *as* *the* lock is taken the
> > > auto mounting doesn't happen. Once you release the lock then
> > > everything will be reprobed and work as it always worked, including
> > > auto-mounting.
> >
> > It is not about delaying the auto mounting, but *preventing it*
> > entirely.
>
> It *is* prevented. While you keep the lock open *no* events are
> propagated from udev to its clients, hence no automounts will take
> place. Any kernel reported event that happen while you keep the lock
> will basically be eaten up by udev and not propagated on to rest of
> userspace. They are sent to /dev/null if you so will. When you release
> the lock once you are fully done (which might as well be 3h later, if
> you like) however, then a single *new* event is *synthesized*, to get
> the rest of userspace updated again on things. And yes, that *might*
> cause userspace to automount things, and other stuff. But that's fine,
> you explicit indicated you are now done with the device, hence others
> can consume it again.

I think you have been talking past each other for the last dozen mails.
I am quite sure that Philip Susi not only wants to prevent auto-mounts
while gparted is working with the filesystem but also afterwards,
i.e. they also want to suppress the synthetic event you are talking about.

> Or in other words: if you must, just take the frickin' lock the
> *entire* time gparted runs, and nothing else will automount or
> otherwise touch device while gparted runs.
>
> Hence, again: just take the frickin' lock. It's the API you should be
> using. Don't mask units or anything, that's entirely besides the
> point and seriously broken.
>
> Did I get through now? I really fail to see why the concept of a lock
> is so difficult to grok?
>
> Lennart
>
> --
> Lennart Poettering, Berlin