On Thu, Apr 18, 2019 at 12:14:58PM -0700, Linus Torvalds wrote: > On Thu, Apr 18, 2019 at 11:58 AM Daniel Colascione <dancol@xxxxxxxxxx> wrote: > > > > On Thu, Apr 18, 2019 at 11:44 AM Jonathan Kowalski <bl0pbl33p@xxxxxxxxx> wrote: > > > > > > Would using something other than POLLIN be an option (maybe POLLPRI)? > > > The convention is to use it to indicate readability on the descriptor, > > > and also possibly POLLHUP instead of POLLERR (the latter is less of a > > > problem, but FreeBSD also does the same, so it'd help with some > > > consistency for libraries wanting to use this, which aren't interested > > > in other sub states). > > > > Existing event loop libraries generally support checking only for > > readability and writability. Not setting POLLIN would make these FDs > > more difficult to use with existing event loop libraries. What > > advantage would compensate for this difficulty? > > Right. > > Usually you'd set POLLIN in _addition_ to any other more specialized poll flag. > > For example, when a socket has shut down the read side, we do > > if (sk->sk_shutdown & RCV_SHUTDOWN) > mask |= EPOLLRDHUP | EPOLLIN | EPOLLRDNORM; > > because while it's true that EPOLLRDHUP is the most _specific_ poll > bit, it's _also_ true that a read shutdown means that the read() will > return immediately. > > So generally a HUP condition should mean that POLLIN and POLLOUT also > get set. Not because there's any actual _data_ to be read, but simply > because the read will not block. Sounds great and I agree with Linus and Daniel. So I am guessing you are Ok with the current set of flags proposed this patch, so I will keep them intact in future patch postings. But please let me know if you want me to change something about the flags. thanks! - Joel
