On Tue, Jan 27, 2015 at 8:49 AM, Jasper St. Pierre <jstpie...@mecheye.net> wrote:
> Gah. I always get those backwards. I actually typed "SCM_RIGHTS" and then > changed it to "SCM_CREDENTIALS". I still don't understand why fd passing is > called "rights". > > On Tue, Jan 27, 2015 at 11:25 AM, Simon McVittie < > simon.mcvit...@collabora.co.uk> wrote: > >> On 27/01/15 15:55, Jasper St. Pierre wrote: >> > Wayland requires two features that would perhaps make it unportable: FD >> > passing (SCM_CREDENTIALS), and shared memory (allocate a temporary >> > files, ftruncate it, mmap it, unlink it and then send the fd across the >> > wire). Everything else is just a simple Unix domain socket. Does OS X >> > support those two features? >> >> I think you mean SCM_RIGHTS? >> >> SCM_RIGHTS is "here's a message with an open fd attached". It's how >> D-Bus does fd-passing, so if D-Bus fd-passing works on your favourite >> platform, Wayland fd-passing should too. >> >> SCM_CREDENTIALS is "here's a message with my uid, gid and pid[1] >> attached, the kernel will check that I haven't lied to you" (also called >> SCM_CREDS on e.g. FreeBSD). Basically every Unix has either this or a >> syscall to query those things or both, but most Unixes also have their >> own unique spelling for the API, because standards are hard.[2] >> >> S >> >> [1] Strictly speaking "the uid, gid and pid I had at the time I opened >> this socket" >> [2] Except that FreeBSD, Dragonfly BSD and Hurd share SCM_CREDS, and >> several platforms (sadly not including Linux) share getpeereid(). For >> the gory details see libdbus source code. > > I put it to the test and tried to build Jasper's proof of concept (and therefore Wayland) on OSX. I didn't get very far. Wayland's configure.ac checks for SFD_CLOEXEC and TFD_CLOEXEC which implies that it uses signalfd() and timerfd(), not available on OSX. I guess the replacement would be something with kqueue though I really haven't the faintest idea what I'm talking about there. Wayland also wants clock_gettime() - not insurmountable to provide on OSX but afaik uses a different API, quick googling showed up this: http://stackoverflow.com/a/6725161/172999 PS. Funny thing that this is one of the top results for googling SFD_CLOEXEC, even without adding "osx" or "wayland": http://stackoverflow.com/questions/27864027/sfd-cloexec-wayland Best, -- Philip
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