Re: [PATCH 2/3] super: wait for nascent superblocks

[Matthew Wilcox <willy@infradead.org>]

On Thu, Aug 17, 2023 at 02:50:21PM +0200, Jan Kara wrote:
> > +/**
> > + * super_wait - wait for superblock to become ready
> > + * @sb: superblock to wait for
> > + * @excl: whether exclusive access is required
> > + *
> > + * If the superblock has neither passed through vfs_get_tree() or
> > + * generic_shutdown_super() yet wait for it to happen. Either superblock
> > + * creation will succeed and SB_BORN is set by vfs_get_tree() or we're
> > + * woken and we'll see SB_DYING.
> > + *
> > + * The caller must have acquired a temporary reference on @sb->s_count.
> > + *
> > + * Return: true if SB_BORN was set, false if SB_DYING was set.
> 
> The comment should mention that this acquires s_umount and returns with it
> held. Also the name is a bit too generic for my taste and not expressing
> the fact this is in fact a lock operation. Maybe something like
> super_lock_wait_born()?

Isn't this actually the normal function we want people to call?  So maybe
this function should be called super_lock() and the functions in the
last patch get called __super_lock() for raw access to the lock.

I'm also a little wary that this isn't _killable.  Are we guaranteed
that a superblock will transition to BORN or DYING within a limited
time?

This isn't part of the VFS I know well.