socket-util: Introduce emulation and wrapper for recvmmsg().

Not every system will have recvmmsg(), so introduce compatibility code
that will allow it to be used blindly from the rest of the tree.

This assumes that recvmmsg() and sendmmsg() are either both present or
both absent in system libraries and headers.

CC: Yi Yang <yangyi01@inspur.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

3 files changed, 74 insertions, 11 deletions

diff --git a/include/sparse/sys/socket.h b/include/sparse/sys/socket.h
index 4178f57e2..d5d7446cf 100644
--- a/include/sparse/sys/socket.h
+++ b/include/sparse/sys/socket.h
@@ -27,6 +27,7 @@
 
 typedef unsigned short int sa_family_t;
 typedef __socklen_t socklen_t;
+struct timespec;
 
 struct sockaddr {
     sa_family_t sa_family;
@@ -126,7 +127,8 @@ enum {
     MSG_PEEK,
     MSG_TRUNC,
     MSG_WAITALL,
-    MSG_DONTWAIT
+    MSG_DONTWAIT,
+    MSG_WAITFORONE
 };
 
 enum {
@@ -163,6 +165,7 @@ ssize_t recvmsg(int, struct msghdr *, int);
 ssize_t send(int, const void *, size_t, int);
 ssize_t sendmsg(int, const struct msghdr *, int);
 int sendmmsg(int, struct mmsghdr *, unsigned int, unsigned int);
+int recvmmsg(int, struct mmsghdr *, unsigned int, int, struct timespec *);
 ssize_t sendto(int, const void *, size_t, int, const struct sockaddr *,
                socklen_t);
 int setsockopt(int, int, int, const void *, socklen_t);
diff --git a/lib/socket-util.c b/lib/socket-util.c
index 6b7378de9..f6f6f3b0a 100644
--- a/lib/socket-util.c
+++ b/lib/socket-util.c
@@ -1283,3 +1283,59 @@ wrap_sendmmsg(int fd, struct mmsghdr *msgs, unsigned int n, unsigned int flags)
 }
 #endif
 #endif
+
+#ifndef _WIN32 /* Avoid using recvmsg on Windows entirely. */
+static int
+emulate_recvmmsg(int fd, struct mmsghdr *msgs, unsigned int n,
+                 int flags, struct timespec *timeout OVS_UNUSED)
+{
+    ovs_assert(!timeout);       /* XXX not emulated */
+
+    bool waitforone = flags & MSG_WAITFORONE;
+    flags &= ~MSG_WAITFORONE;
+
+    for (unsigned int i = 0; i < n; i++) {
+        ssize_t retval = recvmsg(fd, &msgs[i].msg_hdr, flags);
+        if (retval < 0) {
+            return i ? i : retval;
+        }
+        msgs[i].msg_len = retval;
+
+        if (waitforone) {
+            flags |= MSG_DONTWAIT;
+        }
+    }
+    return n;
+}
+
+#ifndef HAVE_SENDMMSG
+int
+recvmmsg(int fd, struct mmsghdr *msgs, unsigned int n,
+         int flags, struct timespec *timeout)
+{
+    return emulate_recvmmsg(fd, msgs, n, flags, timeout);
+}
+#else
+/* recvmmsg was redefined in lib/socket-util.c, should undef recvmmsg here
+ * to avoid recursion */
+#undef recvmmsg
+int
+wrap_recvmmsg(int fd, struct mmsghdr *msgs, unsigned int n,
+              int flags, struct timespec *timeout)
+{
+    ovs_assert(!timeout);       /* XXX not emulated */
+
+    static bool recvmmsg_broken = false;
+    if (!recvmmsg_broken) {
+        int save_errno = errno;
+        int retval = recvmmsg(fd, msgs, n, flags, timeout);
+        if (retval >= 0 || errno != ENOSYS) {
+            return retval;
+        }
+        recvmmsg_broken = true;
+        errno = save_errno;
+    }
+    return emulate_recvmmsg(fd, msgs, n, flags, timeout);
+}
+#endif
+#endif
diff --git a/lib/socket-util.h b/lib/socket-util.h
index a65433d90..71bd68926 100644
--- a/lib/socket-util.h
+++ b/lib/socket-util.h
@@ -104,19 +104,20 @@ int make_unix_socket(int style, bool nonblock,
                      const char *bind_path, const char *connect_path);
 int get_unix_name_len(const struct sockaddr_un *sun, socklen_t sun_len);
 
-/* Universal sendmmsg support.
+/* Universal sendmmsg and recvmmsg support.
  *
- * Some platforms, such as new enough Linux and FreeBSD, support sendmmsg, but
- * other platforms (or older ones) do not.  We add the following infrastructure
- * to allow all code to use sendmmsg, regardless of platform support:
+ * Some platforms, such as new enough Linux and FreeBSD, support sendmmsg and
+ * recvmmsg, but other platforms (or older ones) do not.  We add the following
+ * infrastructure to allow all code to use sendmmsg and recvmmsg, regardless of
+ * platform support:
  *
- *   - For platforms that lack sendmmsg entirely, we emulate it.
+ * - For platforms that lack these functions entirely, we emulate them.
  *
- *   - Some platforms have sendmmsg() in the C library but not in the kernel.
- *     For example, this is true if a Linux system has a newer glibc with an
- *     old kernel.  To compensate, even if sendmmsg() appears to be available,
- *     we still wrap it with a handler that uses our emulation if sendmmsg()
- *     returns ENOSYS.
+ * - Some platforms have sendmmsg() and recvmmsg() in the C library but not in
+ *   the kernel.  For example, this is true if a Linux system has a newer glibc
+ *   with an old kernel.  To compensate, even if these functions appear to be
+ *   available, we still wrap them with handlers that uses our emulation if the
+ *   underlying function returns ENOSYS.
  */
 #ifndef HAVE_STRUCT_MMSGHDR_MSG_LEN
 struct mmsghdr {
@@ -126,9 +127,12 @@ struct mmsghdr {
 #endif
 #ifndef HAVE_SENDMMSG
 int sendmmsg(int, struct mmsghdr *, unsigned int, unsigned int);
+int recvmmsg(int, struct mmsghdr *, unsigned int, int, struct timespec *);
 #else
 #define sendmmsg wrap_sendmmsg
 int wrap_sendmmsg(int, struct mmsghdr *, unsigned int, unsigned int);
+#define recvmmsg wrap_recvmmsg
+int wrap_recvmmsg(int, struct mmsghdr *, unsigned int, int, struct timespec *);
 #endif
 
 /* Helpers for calling ioctl() on an AF_INET socket. */