Replace select() system call with poll()

poll() is specified in POSIX.1-2001 as a simpler interface for
multiplexed file descriptors than select(). It also provides more
functionality.

This PR replaces the select() calls used in xrdp with poll()
equivalents.

xrdpapi/xrdp-ssh-agent.c

@@ -105,6 +105,7 @@
 #include <fcntl.h>
 #include <sys/time.h>
 #include <sys/resource.h>
+#include <poll.h>
 
 #define _PATH_DEVNULL  "/dev/null"
 
@@ -275,14 +276,24 @@ handle_connection(int client_fd)
     int client_going = 1;
     while (client_going)
     {
-        /* Wait for data from RDP or the client */
-        fd_set readfds;
-        FD_ZERO(&readfds);
-        FD_SET(client_fd, &readfds);
-        FD_SET(rdp_fd, &readfds);
-        select(FD_SETSIZE, &readfds, NULL, NULL, NULL);
+        struct pollfd pollfd[2];
+        enum
+        {
+            RDP_FD = 0,
+            CLIENT_FD
+        };
 
-        if (FD_ISSET(rdp_fd, &readfds))
+        /* Wait for data from RDP or the client */
+        pollfd[RDP_FD].fd = rdp_fd;
+        pollfd[RDP_FD].events = POLLIN;
+        pollfd[RDP_FD].revents = 0;
+        pollfd[CLIENT_FD].fd = client_fd;
+        pollfd[CLIENT_FD].events = POLLIN;
+        pollfd[CLIENT_FD].revents = 0;
+
+        poll(pollfd, 2, -1);
+
+        if ((pollfd[RDP_FD].revents & (POLLIN | POLLHUP)) != 0)
         {
             /* Read from RDP and write to the client */
             char buffer[4096];
@@ -325,7 +336,7 @@ handle_connection(int client_fd)
             }
         }
 
-        if (FD_ISSET(client_fd, &readfds))
+        if ((pollfd[CLIENT_FD].revents & (POLLIN | POLLHUP)) != 0)
         {
             /* Read from the client and write to RDP */
             char buffer[4096];
@@ -380,14 +391,18 @@ main(int argc, char **argv)
     /* Wait for a client to connect to the socket */
     while (is_going)
     {
-        fd_set readfds;
-        FD_ZERO(&readfds);
-        FD_SET(sa_uds_fd, &readfds);
-        select(FD_SETSIZE, &readfds, NULL, NULL, NULL);
+        struct pollfd pollfd;
+
+        pollfd.fd = sa_uds_fd;
+        pollfd.events = POLLIN;
+        pollfd.revents = 0;
+
+        poll(pollfd, 1, -1);
 
         /* If something connected then get it...
          * (You can test this using "socat - UNIX-CONNECT:<udspath>".) */
-        if (FD_ISSET(sa_uds_fd, &readfds))
+        if ((pollfd.revents & (POLLIN | POLLHUP)) != 0)
+
         {
             socklen_t addrsize = sizeof(addr);
             int client_fd = accept(sa_uds_fd,

xrdpapi/xrdpapi.c

@@ -32,6 +32,7 @@
 #include <sys/stat.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <poll.h>
 
 #include "log.h"
 #include "xrdp_sockets.h"
@@ -481,40 +482,40 @@ WTSFreeMemory(void *pMemory)
 static int
 can_send(int sck, int millis)
 {
-    struct timeval time;
-    fd_set         wfds;
-    int            select_rv;
+    int rv = 0;
+    struct pollfd pollfd;
 
-    /* setup for a select call */
-    FD_ZERO(&wfds);
-    FD_SET(sck, &wfds);
-    time.tv_sec = millis / 1000;
-    time.tv_usec = (millis * 1000) % 1000000;
+    pollfd.fd = sck;
+    pollfd.events = POLLOUT;
+    pollfd.revents = 0;
+    if (poll(&pollfd, 1, millis) > 0)
+    {
+        if ((pollfd.revents & POLLOUT) != 0)
+        {
+            rv = 1;
+        }
+    }
 
-    /* check if it is ok to write to specified socket */
-    select_rv = select(sck + 1, 0, &wfds, 0, &time);
-
-    return (select_rv > 0) ? 1 : 0;
+    return rv;
 }
 
 /*****************************************************************************/
 static int
 can_recv(int sck, int millis)
 {
-    struct timeval time;
-    fd_set rfds;
-    int select_rv;
+    int rv = 0;
+    struct pollfd pollfd;
 
-    FD_ZERO(&rfds);
-    FD_SET(sck, &rfds);
-    time.tv_sec = millis / 1000;
-    time.tv_usec = (millis * 1000) % 1000000;
-    select_rv = select(sck + 1, &rfds, 0, 0, &time);
-
-    if (select_rv > 0)
+    pollfd.fd = sck;
+    pollfd.events = POLLIN;
+    pollfd.revents = 0;
+    if (poll(&pollfd, 1, millis) > 0)
     {
-        return 1;
+        if ((pollfd.revents & (POLLIN | POLLHUP)) != 0)
+        {
+            rv = 1;
+        }
     }
 
-    return 0;
+    return rv;
 }