Fix alignment issues in FD passing code

[free-sw/xcb/libxcb] / src / xcb_conn.c

diff --git a/src/xcb_conn.c b/src/xcb_conn.c
index e01d566..46390e1 100644 (file)
--- a/src/xcb_conn.c
+++ b/src/xcb_conn.c
@@ -214,9 +214,42 @@ static int write_vec(xcb_connection_t *c, struct iovec **vector, int *count)
     if (n > IOV_MAX)
        n = IOV_MAX;
 
-    n = writev(c->fd, *vector, n);
-    if(n < 0 && errno == EAGAIN)
-        return 1;
+#if HAVE_SENDMSG
+    if (c->out.out_fd.nfd) {
+        union {
+            struct cmsghdr cmsghdr;
+            char buf[CMSG_SPACE(XCB_MAX_PASS_FD * sizeof(int))];
+        } cmsgbuf;
+        struct msghdr msg = {
+            .msg_name = NULL,
+            .msg_namelen = 0,
+            .msg_iov = *vector,
+            .msg_iovlen = n,
+            .msg_control = cmsgbuf.buf,
+            .msg_controllen = CMSG_LEN(c->out.out_fd.nfd * sizeof (int)),
+        };
+        int i;
+        struct cmsghdr *hdr = CMSG_FIRSTHDR(&msg);
+
+        hdr->cmsg_len = msg.msg_controllen;
+        hdr->cmsg_level = SOL_SOCKET;
+        hdr->cmsg_type = SCM_RIGHTS;
+        memcpy(CMSG_DATA(hdr), c->out.out_fd.fd, c->out.out_fd.nfd * sizeof (int));
+
+        n = sendmsg(c->fd, &msg, 0);
+        if(n < 0 && errno == EAGAIN)
+            return 1;
+        for (i = 0; i < c->out.out_fd.nfd; i++)
+            close(c->out.out_fd.fd[i]);
+        c->out.out_fd.nfd = 0;
+    } else
+#endif
+    {
+        n = writev(c->fd, *vector, n);
+        if(n < 0 && errno == EAGAIN)
+            return 1;
+    }
+
 #endif /* _WIN32 */    
 
     if(n <= 0)
@@ -432,15 +465,25 @@ int _xcb_conn_wait(xcb_connection_t *c, pthread_cond_t *cond, struct iovec **vec
 
     if(ret)
     {
+        /* The code allows two threads to call select()/poll() at the same time.
+         * First thread just wants to read, a second thread wants to write, too.
+         * We have to make sure that we don't steal the reading thread's reply
+         * and let it get stuck in select()/poll().
+         * So a thread may read if either:
+         * - There is no other thread that wants to read (the above situation
+         *   did not occur).
+         * - It is the reading thread (above situation occurred).
+         */
+        int may_read = c->in.reading == 1 || !count;
 #if USE_POLL
-        if((fd.revents & POLLIN) == POLLIN)
+        if(may_read && (fd.revents & POLLIN) != 0)
 #else
-        if(FD_ISSET(c->fd, &rfds))
+        if(may_read && FD_ISSET(c->fd, &rfds))
 #endif
             ret = ret && _xcb_in_read(c);
 
 #if USE_POLL
-        if((fd.revents & POLLOUT) == POLLOUT)
+        if((fd.revents & POLLOUT) != 0)
 #else
         if(FD_ISSET(c->fd, &wfds))
 #endif