From 87168807b215b83141220b34ebb30a3e51e61770 Mon Sep 17 00:00:00 2001
From: Viktor Szakats <commit@vsz.me>
Date: Tue, 1 Apr 2025 23:32:16 +0200
Subject: [PATCH] eventfd: fix feature guards

Enable eventfd code consistently when both `HAVE_EVENTFD` and
`HAVE_SYS_EVENTFD_H` macros are defined.

Before this patch `HAVE_EVENTFD` guarded it alone, though the code
also required the header, which was guarded by `HAVE_SYS_EVENTFD_H`.

These should normally be detected in pairs. When they aren't, omit using
`eventfd()` to avoid calling it without a known matching header.

If this disables valid cases (e.g. some system declares this function
via a different header), feature detection and the code may be extended
for those cases. If these are known to come in pairs, always, another
option is detect them both at build stage, and forward a single macro
to C.

Reported-by: Abhinav Singhal
Bug: https://curl.se/mail/lib-2025-04/0000.html
Closes #16909
---
 lib/asyn-thread.c | 4 ++--
 lib/curl_setup.h  | 5 +++++
 lib/multi.c       | 4 ++--
 lib/socketpair.c  | 9 +++++----
 lib/socketpair.h  | 6 +++---
 5 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/lib/asyn-thread.c b/lib/asyn-thread.c
index c3edf72033..177cfc0c7d 100644
--- a/lib/asyn-thread.c
+++ b/lib/asyn-thread.c
@@ -170,7 +170,7 @@ void destroy_thread_sync_data(struct thread_sync_data *tsd)
    * close one end of the socket pair (may be done in resolver thread);
    * the other end (for reading) is always closed in the parent thread.
    */
-#ifndef HAVE_EVENTFD
+#ifndef USE_EVENTFD
   if(tsd->sock_pair[1] != CURL_SOCKET_BAD) {
     wakeup_close(tsd->sock_pair[1]);
   }
@@ -293,7 +293,7 @@ CURL_STDCALL getaddrinfo_thread(void *arg)
   else {
 #ifndef CURL_DISABLE_SOCKETPAIR
     if(tsd->sock_pair[1] != CURL_SOCKET_BAD) {
-#ifdef HAVE_EVENTFD
+#ifdef USE_EVENTFD
       const uint64_t buf[1] = { 1 };
 #else
       const char buf[1] = { 1 };
diff --git a/lib/curl_setup.h b/lib/curl_setup.h
index ff63d3d72f..c5433c02a4 100644
--- a/lib/curl_setup.h
+++ b/lib/curl_setup.h
@@ -455,6 +455,11 @@
 #  define __NO_NET_API
 #endif
 
+/* Whether to use eventfd() */
+#if defined(HAVE_EVENTFD) && defined(HAVE_SYS_EVENTFD_H)
+#define USE_EVENTFD
+#endif
+
 #include <stdio.h>
 #include <assert.h>
 
diff --git a/lib/multi.c b/lib/multi.c
index 09afe804c0..858704beba 100644
--- a/lib/multi.c
+++ b/lib/multi.c
@@ -1408,7 +1408,7 @@ CURLMcode curl_multi_wakeup(CURLM *m)
      and before cleanup */
   if(multi->wakeup_pair[1] != CURL_SOCKET_BAD) {
     while(1) {
-#ifdef HAVE_EVENTFD
+#ifdef USE_EVENTFD
       /* eventfd has a stringent rule of requiring the 8-byte buffer when
          calling write(2) on it */
       const uint64_t buf[1] = { 1 };
@@ -2748,7 +2748,7 @@ CURLMcode curl_multi_cleanup(CURLM *m)
 #else
 #ifdef ENABLE_WAKEUP
     wakeup_close(multi->wakeup_pair[0]);
-#ifndef HAVE_EVENTFD
+#ifndef USE_EVENTFD
     wakeup_close(multi->wakeup_pair[1]);
 #endif
 #endif
diff --git a/lib/socketpair.c b/lib/socketpair.c
index 85fb7a826c..e4ca2cffa0 100644
--- a/lib/socketpair.c
+++ b/lib/socketpair.c
@@ -27,10 +27,9 @@
 #include "urldata.h"
 #include "rand.h"
 
-#ifdef HAVE_EVENTFD
-#ifdef HAVE_SYS_EVENTFD_H
+#ifdef USE_EVENTFD
+
 #include <sys/eventfd.h>
-#endif
 
 int Curl_eventfd(curl_socket_t socks[2], bool nonblocking)
 {
@@ -42,7 +41,9 @@ int Curl_eventfd(curl_socket_t socks[2], bool nonblocking)
   socks[0] = socks[1] = efd;
   return 0;
 }
+
 #elif defined(HAVE_PIPE)
+
 #ifdef HAVE_FCNTL
 #include <fcntl.h>
 #endif
@@ -72,8 +73,8 @@ int Curl_pipe(curl_socket_t socks[2], bool nonblocking)
 
   return 0;
 }
-#endif
 
+#endif /* USE_EVENTFD */
 
 #ifndef CURL_DISABLE_SOCKETPAIR
 #ifdef HAVE_SOCKETPAIR
diff --git a/lib/socketpair.h b/lib/socketpair.h
index da0d08b767..5541899445 100644
--- a/lib/socketpair.h
+++ b/lib/socketpair.h
@@ -26,7 +26,7 @@
 
 #include "curl_setup.h"
 
-#ifdef HAVE_EVENTFD
+#ifdef USE_EVENTFD
 
 #define wakeup_write  write
 #define wakeup_read   read
@@ -46,7 +46,7 @@ int Curl_eventfd(curl_socket_t socks[2], bool nonblocking);
 #include <curl/curl.h>
 int Curl_pipe(curl_socket_t socks[2], bool nonblocking);
 
-#else /* !HAVE_EVENTFD && !HAVE_PIPE */
+#else /* !USE_EVENTFD && !HAVE_PIPE */
 
 #define wakeup_write     swrite
 #define wakeup_read      sread
@@ -69,7 +69,7 @@ int Curl_pipe(curl_socket_t socks[2], bool nonblocking);
 #define wakeup_create(p,nb)\
 Curl_socketpair(SOCKETPAIR_FAMILY, SOCKETPAIR_TYPE, 0, p, nb)
 
-#endif /* HAVE_EVENTFD */
+#endif /* USE_EVENTFD */
 
 #ifndef CURL_DISABLE_SOCKETPAIR
 #include <curl/curl.h>
-- 
2.47.3