On Mon, Nov 26, 2018 at 4:18 PM Florian Weimer <fweimer@xxxxxxxxxx> wrote: > > * Arnd Bergmann: > > > On Thu, Nov 15, 2018 at 7:30 AM Dmitry V. Levin <ldv@xxxxxxxxxxxx> wrote: > >> On Thu, Nov 15, 2018 at 06:39:03AM -0800, Arnd Bergmann wrote: > >> > On Thu, Nov 15, 2018 at 6:05 AM Dmitry V. Levin wrote: > >> > > On Thu, Apr 20, 2017 at 03:20:51PM +0200, Albert ARIBAUD wrote: > >> > >> 1. strace needs a race-free invocation of wait4(2) or waitid(2) > >> with a different signal mask, this cannot be achieved without > >> an extended version of syscall, similar to pselect6(2) extension > >> over select(2) and ppoll(2) extension over poll(2). > >> > >> Signal mask specification in linux requires two parameters: > >> "const sigset_t *sigmask" and "size_t sigsetsize". > >> Creating pwait6(2) as an extension of wait4(2) with two arguments > >> is straightforward. > >> Creating pwaitid(2) as an extension of waitid(2) that already has 5 > >> arguments would require an indirection similar to pselect6(2). > > > > Getting back to this point: you could also do the same thing with > > the CLONE_FD approach from Josh Triplett[1] or Casey Dahlin's > > older waitfd() syscall, correct? > > A descriptor-based solution would not be useful to glibc because > applications assume that glibc does not (persistently) open any file > descriptors behind t heir back. Right, makes sense. What about a temporary file descriptor as discussed in the recent procfd() mail thread then? Would that work? /* for illustration, needs error handling and more features */ int pwait(pid_t id, siginfo_t *infop) { char waitfd_file[MAX_PROCFD_LEN]; struct pollfd pfd[1] = { {.events = POLLIN }}; snprintf(waitfd_file, MAX_PROCFD_LEN, "/proc/%d/wait", pid); pfd.fd = open(waitfd_file, O_RDONLY); ppoll(&pfd, 1, NULL, sigmask); read(fd, infop, sizeof(*infop)); close(fd); return 0; } Arnd