Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> writes: > Introduce a mechanism to quickly disable/enable syscall handling for a > specific process and redirect to userspace via SIGSYS. This is useful > for processes with parts that require syscall redirection and parts that > don't, but who need to perform this boundary crossing really fast, > without paying the cost of a system call to reconfigure syscall handling > on each boundary transition. This is particularly important for Windows > games running over Wine. I raised a discussion about this on libc-alpha, as requested by Florian. At the moment, there was some back and forth on why the use-case is not done by seccomp, but a more interesting point about user_notif was raised by Rich Felker (cc'ed). SIGSYS, as a signal handler, is limited in what can be done inside it. Rich suggested the user_notif design is a better solution. I understand that from a Wine perspective, SIGSYS suffices for their work, but would it make sense to extend SUD interface to support a user_notif-like interface? Would this be acceptable as future work to be added when/if needed, or should we design it from the start? The existing interface could be extended with a flags field as part of the opcode passed in argument 2, which is currently reserved, and then return a FD, just like seccomp(2) does. So it is not like the current patches couldn't be extended in the future if needed, unless I'm mistaken. -- Gabriel Krisman Bertazi
