Andrew Morton wrote:
> On Mon, 11 Feb 2008 15:16:54 +0100
> Nadia.Derbey@bull.net 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