poll-rather-than-select.patch

From a1b3c1faa53c8c51aa52361bf7035d6fc91b747d Mon Sep 17 00:00:00 2001
From: garethsb-sony <gareth.sylvester-bradley@sony.com>
Date: Mon, 26 Feb 2018 12:58:27 +0000
Subject: [PATCH] On Linux, use poll rather than select to wait on the socket

---
 .../mDNSShared/dnssd_clientstub.c    | 77 ++++++++--------------
 1 file changed, 30 insertions(+), 47 deletions(-)

diff --git a/mDNSShared/dnssd_clientstub.c b/mDNSShared/dnssd_clientstub.c
index 27e90ee..d0bfcd3 100644
--- a/mDNSShared/dnssd_clientstub.c
+++ b/mDNSShared/dnssd_clientstub.c
@@ -80,6 +80,7 @@ static void syslog( int priority, const char * message, ...)
 }
 #else
 
+    #include <poll.h>
     #include <sys/fcntl.h>      // For O_RDWR etc.
     #include <sys/time.h>
     #include <sys/socket.h>
@@ -283,46 +284,23 @@ static int read_all(dnssd_sock_t sd, char *buf, int len)
 // Returns 1 if more bytes remain to be read on socket descriptor sd, 0 otherwise
 static int more_bytes(dnssd_sock_t sd)
 {
-    struct timeval tv = { 0, 0 };
-    fd_set readfds;
-    fd_set *fs;
     int ret;
 
 #if defined(_WIN32)
-    fs = &readfds;
-    FD_ZERO(fs);
-    FD_SET(sd, fs);
-    ret = select((int)sd+1, fs, (fd_set*)NULL, (fd_set*)NULL, &tv);
+    struct timeval tv = { 0, 0 };
+    fd_set readfds;
+    FD_ZERO(&readfds);
+    FD_SET(sd, &readfds);
+    ret = select((int)sd+1, &readfds, (fd_set*)NULL, (fd_set*)NULL, &tv);
 #else
-    if (sd < FD_SETSIZE)
-    {
-        fs = &readfds;
-        FD_ZERO(fs);
-    }
-    else
-    {
-        // Compute the number of integers needed for storing "sd". Internally fd_set is stored
-        // as an array of ints with one bit for each fd and hence we need to compute
-        // the number of ints needed rather than the number of bytes. If "sd" is 32, we need
-        // two ints and not just one.
-        int nfdbits = sizeof (int) * 8;
-        int nints = (sd/nfdbits) + 1;
-        fs = (fd_set *)calloc(nints, (size_t)sizeof(int));
-        if (fs == NULL) 
-        { 
-            syslog(LOG_WARNING, "dnssd_clientstub more_bytes: malloc failed"); 
-            return 0; 
-        }
-    }
-    FD_SET(sd, fs);
-    ret = select((int)sd+1, fs, (fd_set*)NULL, (fd_set*)NULL, &tv);
-    if (fs != &readfds) 
-        free(fs);
+    // Use poll in order to be able to wait for a file descriptor larger than FD_SETSIZE
+    struct pollfd pfd_read = { sd, POLLIN, 0 };
+    ret = poll(&pfd_read, 1, 0);
 #endif
     return (ret > 0);
 }
 
-// set_waitlimit() implements a timeout using select. It is called from deliver_request() before recv() OR accept()
+// set_waitlimit() implements a timeout using select or poll. It is called from deliver_request() before recv() OR accept()
 // to ensure the UDS clients are not blocked in these system calls indefinitely.
 // Note: Ideally one should never be blocked here, because it indicates either mDNSResponder daemon is not yet up/hung/
 // superbusy/crashed or some other OS bug. For eg: On Windows which suffers from 3rd party software 
@@ -331,23 +309,28 @@ static int more_bytes(dnssd_sock_t sd)
 static int set_waitlimit(dnssd_sock_t sock, int timeout)
 {
     int gDaemonErr = kDNSServiceErr_NoError;
+    int ret;
 
-    // To prevent stack corruption since select does not work with timeout if fds > FD_SETSIZE(1024)
-    if (!gDaemonErr && sock < FD_SETSIZE)
-    {
-        struct timeval tv;
-        fd_set set;
+#if defined(_WIN32)
+    struct timeval tv;
+    fd_set set;
+
+    FD_ZERO(&set);
+    FD_SET(sock, &set);
+    tv.tv_sec = timeout;
+    tv.tv_usec = 0;
+    ret = select((int)(sock + 1), &set, NULL, NULL, &tv);
+#else
+    // Use poll in order to be able to wait for a file descriptor larger than FD_SETSIZE
+    struct pollfd pfd_read = { sock, POLLIN, 0 };
+    ret = poll(&pfd_read, 1, timeout * 1000);
+#endif
 
-        FD_ZERO(&set);
-        FD_SET(sock, &set);
-        tv.tv_sec = timeout;
-        tv.tv_usec = 0;
-        if (!select((int)(sock + 1), &set, NULL, NULL, &tv))
-        {
-            // Ideally one should never hit this case: See comments before set_waitlimit()
-            syslog(LOG_WARNING, "dnssd_clientstub set_waitlimit:_daemon timed out (%d secs) without any response: Socket %d", timeout, sock);
-            gDaemonErr = kDNSServiceErr_Timeout;
-        }
+    if (!(ret > 0))
+    {
+        // Ideally one should never hit this case: See comments before set_waitlimit()
+        syslog(LOG_WARNING, "dnssd_clientstub set_waitlimit:_daemon timed out (%d secs) without any response: Socket %d", timeout, sock);
+        gDaemonErr = kDNSServiceErr_Timeout;
     }
     return gDaemonErr;
 }