On Fri, Nov 30, 2018 at 12:29:21PM +0100, Oleg Nesterov wrote:

On 11/30, Dmitry V. Levin wrote:

quoted

On Thu, Nov 29, 2018 at 03:47:43PM +0100, Oleg Nesterov wrote:

quoted

quoted

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