On Fri, Nov 30, 2018 at 12:29:21PM +0100, Oleg Nesterov wrote:
> On 11/30, Dmitry V. Levin wrote:
> > On Thu, Nov 29, 2018 at 03:47:43PM +0100, Oleg Nesterov wrote:
> >
> > > > so that PTRACE_GETEVENTMSG users can easily tell
> > > > whether this new semantics is supported by the kernel or not.
> > >
> > > Yes. And how much this can help? Again, an application can trivially detect
> > > if this feature implemented or not, and it should do this anyway if it wants
> > > to (try to) use PTRACE_EVENTMSG_SYSCALL_ENTRY/EXIT ?
> >
> > How an application can easily detect whether this feature is implemented?
> 
> As I already said, it can just do ptrace(PTRACE_GET_SYSCALL_INFO, NULL) ?
> If it returns -EIO then this feature is not implemented. Any other error
> code (actually EINVAL or EFAULT) means it is implemented.

Fair enough.
We can change PTRACE_EVENTMSG_SYSCALL_ENTRY/EXIT to 1/2 if you like,
and document this trick somewhere.


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ldv