Re: [PATCH 05/11] quota: Allow to pass quotactl a mountpoint

[Al Viro <viro@xxxxxxxxxxxxxxxxxx>]

On Thu, Aug 15, 2019 at 12:36:32AM +0100, Al Viro wrote:
> On Wed, Aug 14, 2019 at 02:18:28PM +0200, Sascha Hauer wrote:
> > +/**
> > + * reference_super - get a reference to a given superblock
> > + * @sb: superblock to get the reference from
> > + *
> > + * Takes a reference to a superblock. Can be used as when the superblock
> > + * is known and leaves it in a state as if get_super had been called.
> > + */
> > +void reference_super(struct super_block *sb)
> > +{
> > +	spin_lock(&sb_lock);
> > +	sb->s_count++;
> > +	spin_unlock(&sb_lock);
> > +
> > +	down_read(&sb->s_umount);
> > +}
> > +EXPORT_SYMBOL_GPL(reference_super);
> 
> NAK, for a plenty of reasons
> 
> 1) introduction of EXPORT_SYMBOL_GPL garbage
> 2) aforementioned garbage on something that doesn't need to be exported
> 3) *way* too easily abused - get_super() is, at least, not tempting to
> play with in random code.  This one is, and it's too low-level to
> allow.

... and this is a crap userland API.

*IF* you want mountpoint-based variants of quotactl() commands, by all means,
add those.  Do not overload the old ones.  And for path-based you don't
need to mess with superblock references - just keep the struct path until
the end.  That will keep the superblock alive and active just fine.

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