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