Alexander Viro writes:
>
>
> On Sat, 10 Jun 2000, Richard Gooch wrote:
>
> > Hi, all. I've just been looking at the FS_SINGLE implementation, and
> > have a few comments:
> >
> > - although not documented, you need to do kern_mount() before trying
> Yup.
> > normal mounts of a FS_SINGLE; perhaps kern_mount()/kern_umount()
> > should be called automatically in
> > register_filesystem()/unregister_filesystem()?
>
> I don't think so. They are different operations and I'm not too happy
> about mixing them together. Matter of taste, but...
Yeah, I know. Having it documented would satisfy me. Getting a kernel
BUG after adding FS_SINGLE was a shock: "what the %@$& ?!?".
> > - I note that procfs and pipefs call unregister_filesystem() before
> > calling kern_umount(). This looks counter-intuitive, even if it's
> > correct (is it?)
>
> It is. Look: first you take it out of reach so that nobody would
> mount us while we are doing kern_umount(), then you kill the tree.
I suspected it was about race prevention. Again, if it was documented,
it would be fine. When I first saw the procfs/pipefs code, I was left
wondering if it was safe to unregister before unmounting.
> > - when mounting a FS which is FS_SINGLE, /proc/mounts reports the FS
> > type rather than "bind", which also seems wrong.
>
> Why? Bind is _not_ a filesystem type. From the kernel point of view
> old and new instances after binding are identical - there is no
> asymmetry.
I see your point. However, that suggests that the naming of
/proc/mounts is wrong. Perhaps we should have a /proc/namespace that
shows all these VFS bindings, and separately a list of real mounts.
I have the feeling we're mixing two different pieces of information
into /proc/mounts at the moment.
Regards,
Richard....
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