[Qemu-devel] [PATCH v3] slirp: check for ioctlsocket error and 0-length udp payload.

[Vic Lee]

Sometimes sorecvfrom() is called from slirp.c because revents == G_IO_IN,
but there is 0 bytes available and recvfrom could be blocking indefinitely.
This is likely due to 0-length udp payload. This also adds an error
checking for ioctlsocket.

Signed-off-by: Vic Lee <address@hidden>
---
 slirp/socket.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/slirp/socket.c b/slirp/socket.c
index 4876ea3f31..af732f78fb 100644
--- a/slirp/socket.c
+++ b/slirp/socket.c
@@ -529,6 +529,15 @@ sorecvfrom(struct socket *so)
           int n;
 #endif
 
+            if (ioctlsocket(so->s, FIONREAD, &n) != 0) {
+                DEBUG_MISC((dfd, " ioctlsocket errno = %d-%s\n",
+                            errno, strerror(errno)));
+                return;
+            }
+            if (n == 0) {
+                return;
+            }
+
          m = m_get(so->slirp);
          if (!m) {
              return;
@@ -552,7 +561,6 @@ sorecvfrom(struct socket *so)
           */
          len = M_FREEROOM(m);
          /* if (so->so_fport != htons(53)) { */
-         ioctlsocket(so->s, FIONREAD, &n);
 
          if (n > len) {
            n = (m->m_data - m->m_dat) + m->m_len + n + 1;
-- 
2.20.1