2 files changed, 20 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 688e8c109..a6b547198 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,10 @@
      [authfile.c]
      Fix bug introduced in r1.78 (incorrect brace location) that broke key auth.
      Patch from joachim joachimschipper nl.
+   - djm@cvs.openbsd.org 2010/01/12 00:58:25
+     [monitor_fdpass.c]
+     avoid spinning when fd passing on nonblocking sockets by calling poll()
+     in the EINTR/EAGAIN path, much like we do in atomicio; ok dtucker@
 
 20100110
  - (dtucker) [configure.ac misc.c readconf.c servconf.c ssh-keyscan.c]
diff --git a/monitor_fdpass.c b/monitor_fdpass.c
index 4b9a066bc..56d3afdf3 100644
--- a/monitor_fdpass.c
+++ b/monitor_fdpass.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: monitor_fdpass.c,v 1.18 2008/11/30 11:59:26 dtucker Exp $ */
+/* $OpenBSD: monitor_fdpass.c,v 1.19 2010/01/12 00:58:25 djm Exp $ */
 /*
  * Copyright 2001 Niels Provos <provos@citi.umich.edu>
  * All rights reserved.
@@ -34,6 +34,7 @@
 #endif
 
 #include <errno.h>
+#include <poll.h>
 #include <string.h>
 #include <stdarg.h>
 
@@ -55,6 +56,7 @@ mm_send_fd(int sock, int fd)
         struct iovec vec;
         char ch = '\0';
         ssize_t n;
+        struct pollfd pfd;
 
         memset(&msg, 0, sizeof(msg));
 #ifdef HAVE_ACCRIGHTS_IN_MSGHDR
@@ -75,9 +77,13 @@ mm_send_fd(int sock, int fd)
         msg.msg_iov = &vec;
         msg.msg_iovlen = 1;
 
-        while ((n = sendmsg(sock, &msg, 0)) == -1 && (errno == EAGAIN ||
-            errno == EINTR))
+        pfd.fd = sock;
+        pfd.events = POLLOUT;
+        while ((n = sendmsg(sock, &msg, 0)) == -1 &&
+            (errno == EAGAIN || errno == EINTR)) {
                 debug3("%s: sendmsg(%d): %s", __func__, fd, strerror(errno));
+                (void)poll(&pfd, 1, -1);
+        }
         if (n == -1) {
                 error("%s: sendmsg(%d): %s", __func__, fd,
                     strerror(errno));
@@ -112,6 +118,7 @@ mm_receive_fd(int sock)
         ssize_t n;
         char ch;
         int fd;
+        struct pollfd pfd;
 
         memset(&msg, 0, sizeof(msg));
         vec.iov_base = &ch;
@@ -126,9 +133,13 @@ mm_receive_fd(int sock)
         msg.msg_controllen = sizeof(cmsgbuf.buf);
 #endif
 
-        while ((n = recvmsg(sock, &msg, 0)) == -1 && (errno == EAGAIN ||
-            errno == EINTR))
+        pfd.fd = sock;
+        pfd.events = POLLIN;
+        while ((n = recvmsg(sock, &msg, 0)) == -1 &&
+            (errno == EAGAIN || errno == EINTR)) {
                 debug3("%s: recvmsg: %s", __func__, strerror(errno));
+                (void)poll(&pfd, 1, -1);
+        }
         if (n == -1) {
                 error("%s: recvmsg: %s", __func__, strerror(errno));
                 return -1;