From af9d45719fa8f22e6d90a774540d172b9d8ac03a Mon Sep 17 00:00:00 2001
From: "Nicholas J. Kain" <nicholas@kain.us>
Date: Tue, 20 Oct 2020 05:09:26 -0400
Subject: [PATCH] Use poll() instead of epoll() for ifchd and sockd.

poll() is simpler, portable, and the scalability advantages of
epoll are inapplicable here.
---
 src/ifchd.c | 47 ++++++++++++++++++++---------------------------
 src/sockd.c | 47 ++++++++++++++++++++---------------------------
 2 files changed, 40 insertions(+), 54 deletions(-)

diff --git a/src/ifchd.c b/src/ifchd.c
index ddfcc8f..31d314f 100644
--- a/src/ifchd.c
+++ b/src/ifchd.c
@@ -34,7 +34,7 @@
 #include <sys/un.h>
 #include <sys/time.h>
 #include <sys/types.h>
-#include <sys/epoll.h>
+#include <poll.h>
 #include <sys/prctl.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -53,10 +53,6 @@
 
 struct ifchd_client cl;
 
-static int epollfd;
-/* Slots are for the ndhc -> ifchd socket. */
-static struct epoll_event events[2];
-
 static int resolv_conf_fd = -1;
 /* int ntp_conf_fd = -1; */
 static int resolv_conf_head_fd = -1;
@@ -341,36 +337,33 @@ static void process_client_socket(void)
 
 static void do_ifch_work(void)
 {
-    epollfd = epoll_create1(0);
-    if (epollfd < 0)
-        suicide("epoll_create1 failed");
-
     cl.state = STATE_NOTHING;
     memset(cl.ibuf, 0, sizeof cl.ibuf);
     memset(cl.namesvrs, 0, sizeof cl.namesvrs);
     memset(cl.domains, 0, sizeof cl.domains);
 
-    epoll_add(epollfd, ifchSock[1]);
-    epoll_add(epollfd, ifchStream[1]);
+    struct pollfd pfds[2] = {0};
+    pfds[0].fd = ifchSock[1];
+    pfds[0].events = POLLIN|POLLHUP|POLLERR|POLLRDHUP;
+    pfds[1].fd = ifchStream[1];
+    pfds[1].events = POLLHUP|POLLERR|POLLRDHUP;
 
     for (;;) {
-        int r = epoll_wait(epollfd, events, 2, -1);
-        if (r < 0) {
-            if (errno == EINTR)
-                continue;
-            else
-                suicide("epoll_wait failed");
+        if (poll(pfds, 2, -1) < 0) {
+            if (errno == EINTR) continue;
+            else suicide("pollt failed");
         }
-        for (int i = 0; i < r; ++i) {
-            int fd = events[i].data.fd;
-            if (fd == ifchSock[1]) {
-                if (events[i].events & EPOLLIN)
-                    process_client_socket();
-            } else if (fd == ifchStream[1]) {
-                if (events[i].events & (EPOLLHUP|EPOLLERR|EPOLLRDHUP))
-                    exit(EXIT_SUCCESS);
-            } else
-                suicide("ifch: unexpected fd while performing epoll");
+        if (pfds[0].revents & POLLIN) {
+            pfds[0].revents &= ~POLLIN;
+            process_client_socket();
+        }
+        if (pfds[0].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
+            pfds[0].revents &= ~(POLLHUP|POLLERR|POLLRDHUP);
+            suicide("ifchSock closed unexpectedly");
+        }
+        if (pfds[1].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
+            pfds[1].revents &= ~(POLLHUP|POLLERR|POLLRDHUP);
+            exit(EXIT_SUCCESS);
         }
     }
 }
diff --git a/src/sockd.c b/src/sockd.c
index 6beed09..a50224a 100644
--- a/src/sockd.c
+++ b/src/sockd.c
@@ -36,7 +36,7 @@
 #include <fcntl.h>
 #include <assert.h>
 #include <sys/socket.h>
-#include <sys/epoll.h>
+#include <poll.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/prctl.h>
@@ -58,10 +58,6 @@
 #include "dhcp.h"
 #include "sys.h"
 
-static int epollfd;
-/* Slots are for the ndhc -> ifchd socket. */
-static struct epoll_event events[2];
-
 uid_t sockd_uid = 0;
 gid_t sockd_gid = 0;
 
@@ -550,31 +546,28 @@ static void process_client_socket(void)
 
 static void do_sockd_work(void)
 {
-    epollfd = epoll_create1(0);
-    if (epollfd < 0)
-        suicide("epoll_create1 failed");
-
-    epoll_add(epollfd, sockdSock[1]);
-    epoll_add(epollfd, sockdStream[1]);
+    struct pollfd pfds[2] = {0};
+    pfds[0].fd = sockdSock[1];
+    pfds[0].events = POLLIN|POLLHUP|POLLERR|POLLRDHUP;
+    pfds[1].fd = sockdStream[1];
+    pfds[1].events = POLLHUP|POLLERR|POLLRDHUP;
 
     for (;;) {
-        int r = epoll_wait(epollfd, events, 2, -1);
-        if (r < 0) {
-            if (errno == EINTR)
-                continue;
-            else
-                suicide("epoll_wait failed");
+        if (poll(pfds, 2, -1) < 0) {
+            if (errno == EINTR) continue;
+            else suicide("poll failed");
         }
-        for (int i = 0; i < r; ++i) {
-            int fd = events[i].data.fd;
-            if (fd == sockdSock[1]) {
-                if (events[i].events & EPOLLIN)
-                    process_client_socket();
-            } else if (fd == sockdStream[1]) {
-                if (events[i].events & (EPOLLHUP|EPOLLERR|EPOLLRDHUP))
-                    exit(EXIT_SUCCESS);
-            } else
-                suicide("sockd: unexpected fd while performing epoll");
+        if (pfds[0].revents & POLLIN) {
+            pfds[0].revents &= ~POLLIN;
+            process_client_socket();
+        }
+        if (pfds[0].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
+            pfds[0].revents &= ~(POLLHUP|POLLERR|POLLRDHUP);
+            suicide("sockdSock closed unexpectedly");
+        }
+        if (pfds[1].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
+            pfds[1].revents &= ~(POLLHUP|POLLERR|POLLRDHUP);
+            exit(EXIT_SUCCESS);
         }
     }
 }