Re: [PATCH 8/8] Re-enable msgmni automatic recomputing msgmni ifset to negative

[Nadia Derbey]

Andrew Morton wrote:
> On Mon, 11 Feb 2008 15:16:54 +0100
> Nadia.Derbey@xxxxxxxx wrote:
>
>
> > [PATCH 08/08]
> >
> > This patch is the enhancement as asked for by Yasunori: if msgmni is set to
> > a negative value, register it back into the ipcns notifier chain.
> >
> > A new interface has been added to the notification mechanism:
> > notifier_chain_cond_register() registers a notifier block only if not already
> > registered. With that new interface we avoid taking care of the states changes
> > in procfs.
> >
> > ...
> >
> > static int proc_ipc_callback_dointvec(ctl_table *table, int write,
> > 	struct file *filp, void __user *buffer, size_t *lenp, loff_t *ppos)
> > {
> > +	struct ctl_table ipc_table;
> > 	size_t lenp_bef = *lenp;
> > 	int rc;
> >
> > -	rc = proc_ipc_dointvec(table, write, filp, buffer, lenp, ppos);
> > +	memcpy(&ipc_table, table, sizeof(ipc_table));
> > +	ipc_table.data = get_ipc(table);
> > +
> > +	rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
> >
> > 	if (write && !rc && lenp_bef == *lenp)
> > -		/*
> > -		 * Tunable has successfully been changed from userland:
> > -		 * disable its automatic recomputing.
> > -		 */
> > -		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
> > +		tunable_set_callback(*((int *)(ipc_table.data)));
> >
> > 	return rc;
> > }
> > @@ -119,12 +142,14 @@ static int sysctl_ipc_registered_data(ct
> > 	rc = sysctl_ipc_data(table, name, nlen, oldval, oldlenp, newval,
> > 		newlen);
> >
> > -	if (newval && newlen && rc > 0)
> > +	if (newval && newlen && rc > 0) {
> > 		/*
> > -		 * Tunable has successfully been changed from userland:
> > -		 * disable its automatic recomputing.
> > +		 * Tunable has successfully been changed from userland
> > 		 */
> > -		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
> > +		int *data = get_ipc(table);
> > +
> > +		tunable_set_callback(*data);
> > +	}
> >
> > 	return rc;
> > }
>
>
> hm, what's happening here?  We take a local copy of the caller's ctl_table
> and then pass that into proc_dointvec().  Is that as hacky as it seems??

Well, the caller's ctl_table contains the tunables addresses for the 
init namspeace in its .data fields. While what needs to be passed in to 
proc_dointvec() is the tunable address in the caller's namespace.
Since all the fields in ipc_kern_table[] are ok but the .data one, imho 
it's correct to store it in a local copy and change the data field to 
the appropirate one, before passing it to proc_dointvec().

Regards,
Nadia
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