From 3850d27f47a887a958ded828f6ce8de4e791037c Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Tue, 22 Nov 2022 15:23:34 +0100 Subject: [PATCH] io-util: document EINTR situation a bit (cherry picked from commit ffbcc8d423671ad2fe827e4823a8032dc1f0a8b3) Related: #2137584 --- src/basic/io-util.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/src/basic/io-util.c b/src/basic/io-util.c index cdad939aa6..f642beca3a 100644 --- a/src/basic/io-util.c +++ b/src/basic/io-util.c @@ -161,6 +161,21 @@ int ppoll_usec(struct pollfd *fds, size_t nfds, usec_t timeout) { assert(fds || nfds == 0); + /* This is a wrapper around ppoll() that does primarily two things: + * + * ✅ Takes a usec_t instead of a struct timespec + * + * ✅ Guarantees that if an invalid fd is specified we return EBADF (i.e. converts POLLNVAL to + * EBADF). This is done because EBADF is a programming error usually, and hence should bubble up + * as error, and not be eaten up as non-error POLLNVAL event. + * + * ⚠️ ⚠️ ⚠️ Note that this function does not add any special handling for EINTR. Don't forget + * poll()/ppoll() will return with EINTR on any received signal always, there is no automatic + * restarting via SA_RESTART available. Thus, typically you want to handle EINTR not as an error, + * but just as reason to restart things, under the assumption you use a more appropriate mechanism + * to handle signals, such as signalfd() or signal handlers. ⚠️ ⚠️ ⚠️ + */ + if (nfds == 0) return 0; @@ -188,6 +203,9 @@ int fd_wait_for_event(int fd, int event, usec_t timeout) { }; int r; + /* ⚠️ ⚠️ ⚠️ Keep in mind you almost certainly want to handle -EINTR gracefully in the caller, see + * ppoll_usec() above! ⚠️ ⚠️ ⚠️ */ + r = ppoll_usec(&pollfd, 1, timeout); if (r <= 0) return r;