On Wed, Sep 12, 2018 at 04:52:38PM -0700, Andy Lutomirski wrote: > On Thu, Sep 6, 2018 at 8:28 AM, Tycho Andersen <tycho@xxxxxxxx> wrote: > > The idea here is that the userspace handler should be able to pass an fd > > back to the trapped task, for example so it can be returned from socket(). > > > > I've proposed one API here, but I'm open to other options. In particular, > > this only lets you return an fd from a syscall, which may not be enough in > > all cases. For example, if an fd is written to an output parameter instead > > of returned, the current API can't handle this. Another case is that > > netlink takes as input fds sometimes (IFLA_NET_NS_FD, e.g.). If netlink > > ever decides to install an fd and output it, we wouldn't be able to handle > > this either. > > An alternative could be to have an API (an ioctl on the listener, > perhaps) that just copies an fd into the tracee. There would be the > obvious set of options: do we replace an existing fd or allocate a new > one, and is it CLOEXEC. Then the tracer could add an fd and then > return it just like it's a regular number. > > I feel like this would be more flexible and conceptually simpler, but > maybe a little slower for the common cases. What do you think? Yes, I like this. It also future (or current-) proofs the API against instances where we return an FD in a structure and not via the return code of the syscall. Tycho
