Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO request

[Oleg Nesterov <oleg@redhat.com>]

Dmitry,

You certainly understand the user-space needs much better than me.
I am just trying to understand your point.

On 01/17, Dmitry V. Levin wrote:
>
> We should accept larger user_size from the very beginning, so that in case
> the structure grows in the future, the userspace that sicks to the current
> set of supported features would be still able to work with older kernels.

This is what I can't understand, perhaps I have a blind spot here ;)

Could you provide an example (even absolutely artificial) of possible extension
which can help me to understand?

> We cannot just use sizeof(info) because it depends on the alignment of
> __u64.

Hmm why? I thought that the kernel already depends on the "natural" alignment?
And if we can't, then PTRACE_SYSCALL_INFO_SIZE_VER0 added by this patch makes
no sense?

Sorry I guess I must have missed something, I am sick today.

> Also, I don't think we need to fill with zeroes the trailing
> padding bytes of the structure as we are not going to use them in any way.

At least we seem to agree here ;)

Oleg.