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

[Jan Kara <jack@xxxxxxx>]

On Wed 29-01-20 01:29:29, Al Viro wrote:
> On Tue, Jan 28, 2020 at 11:06:31AM +0100, Sascha Hauer wrote:
> > Hi Jan,
> 
> > @@ -810,6 +811,36 @@ static struct super_block *quotactl_block(const char __user *special, int cmd)
> >  #endif
> >  }
> >  
> > +static struct super_block *quotactl_path(const char __user *special, int cmd,
> > +					 struct path *path)
> > +{
> > +	struct super_block *sb;
> > +	int ret;
> > +
> > +	ret = user_path_at(AT_FDCWD, special, LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> > +			   path);
> > +	if (ret)
> > +		return ERR_PTR(ret);
> > +
> > +	sb = path->mnt->mnt_sb;
> > +restart:
> > +	if (quotactl_cmd_onoff(cmd))
> > +		down_write(&sb->s_umount);
> > +	else
> > +		down_read(&sb->s_umount);
> > +
> > +	if (quotactl_cmd_write(cmd) && sb->s_writers.frozen != SB_UNFROZEN) {
> > +		if (quotactl_cmd_onoff(cmd))
> > +			up_write(&sb->s_umount);
> > +		else
> > +			up_read(&sb->s_umount);
> > +		wait_event(sb->s_writers.wait_unfrozen,
> > +			   sb->s_writers.frozen == SB_UNFROZEN);
> > +		goto restart;
> > +	}
> > +
> > +	return sb;
> > +}
> 
> This partial duplicate of __get_super_thawed() guts does *not* belong here,
> especially not interleaved with quota-specific checks.

OK, so some primitive in fs/super.c like:

void hold_super_thawed(struct super_block *sb, bool excl);

that would implement the above functionality and grab passive reference?

> > +	if (q_path) {
> > +		if (quotactl_cmd_onoff(cmd))
> > +			up_write(&sb->s_umount);
> > +		else
> > +			up_read(&sb->s_umount);
> > +
> > +		path_put(&sb_path);
> > +	} else {
> > +		if (!quotactl_cmd_onoff(cmds))
> > +			drop_super(sb);
> > +		else
> > +			drop_super_exclusive(sb);
> > +	}
> 
> Er...  Why not have the same code that you've used to lock the damn thing
> (needs to be moved to fs/super.c) simply get a passive ref to it?  Then
> you could do the same thing, q_path or no q_path...

Yes.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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