[PATCH] An attempt to have an unlimitedly extendable sys_clone

Daniel Hokka Zakrisson daniel at hozac.com
Tue Jan 15 23:58:51 PST 2008

Pavel Emelyanov wrote:
> [snip]
>>> +static struct long_clone_arg *get_long_clone_arg(int __user
>>> *child_tidptr)
>>> +{
>>> +	int size;
>>> +	struct long_clone_arg *carg;
>>> +
>>> +	if (get_user(size, child_tidptr))
>>> +		return ERR_PTR(-EFAULT);
>>> +
>>> +	if (size > sizeof(struct long_clone_arg))
>>> +		return ERR_PTR(-EINVAL);
>> This means that software built against a newer kernel won't work on an
>> older one. Surely that's not intended?
> It is intended. If I ask an old kernel to clone the mq namespace, but
> it doesn't support such, that I'd better like to get an -EINVAL error
> rather than be silently held in an old global namespace.

That rules out using the struct for things like child_tidptr, the desired
pid for C/R, etc. I think the version Dave Hansen proposed would be
better, or if it's really just for bits, use an array rather than a struct
to make that obvious.

> [snip]

Daniel Hokka Zakrisson

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