Re: [PATCH v2 2/4] exit: support non-blocking pidfds

On Thu, Sep 03, 2020 at 04:22:42PM +0200, Oleg Nesterov wrote:

On 09/02, Christian Brauner wrote:

quoted

It also makes the API more consistent and uniform. In essence, waitid() is
treated like a read on a non-blocking pidfd or a recvmsg() on a non-blocking
socket.
With the addition of support for non-blocking pidfds we support the same
functionality that sockets do. For sockets() recvmsg() supports MSG_DONTWAIT
for pidfds waitid() supports WNOHANG.

What I personally do not like is that waitid(WNOHANG) returns zero or EAGAIN
depending on f_flags & O_NONBLOCK... This doesn't match recvmsg(MSG_DONTWAIT)
and doesn't look consistent to me.

It's not my favorite thing either but async event loops are usually
modeled around EAGAIN so I think this has benefits. Josh can speak more
to that.

Christian