Re: [PATCH 1/8] quota: Allow to pass mount path to quotactl

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jan 25, 2021 at 04:45:07PM +0100, Jan Kara wrote:
> > What do you mean by "take"? Take the superblock as an argument to
> > quotactl_sb() or take a reference to the superblock?
> > Sorry, I don't really get where you aiming at.
> 
> I think Christoph was pointing at the fact it is suboptimal to search for
> superblock by device number when you already have a pointer to it.  And I
> guess he was suggesting we could pass 'sb' pointer to quotactl_sb() when we
> already have it. Although to be honest, I'm not sure how Christoph imagines
> the refactoring of user_get_super() he mentions - when we have a path
> looked up through user_path(), that pins the superblock the path is on so
> it cannot be unmounted. So perhaps quotactl_sb() can done like:

I don't think we need a quotactl_sb at all, do_quotactl is in fact a
pretty good abstraction as-is.

For the path based one we just need to factor out a little helper
to set excl and thaw and then call it like:

	sb = path.dentry->d_inode->i_sb;

	if (excl)
		down_write(&sb->s_umount);
	else
		down_read(&sb->s_umount);
	if (thawed && sb->s_writers.frozen != SB_UNFROZEN)
		ret = -EBUSY;
	else
		ret = do_quotactl(sb, type, cmds, id, addr, &path);
	if (excl)
		up_write(&sb->s_umount);
	else
		up_read(&sb->s_umount);

as there is no good reason to bring over the somewhat strange wait until
unfrozen semantics to a new syscall.

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