swrap: Add environment variable to specify mtu size

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

diff --git a/lib/socket_wrapper/socket_wrapper.c b/lib/socket_wrapper/socket_wrapper.c
index 18622af27a0c3cf26dfc471c65531bc6b85dbf9e..01ab8d52d38d23ad703bc634fe531efc34a8f6f7 100644 (file)
--- a/lib/socket_wrapper/socket_wrapper.c
+++ b/lib/socket_wrapper/socket_wrapper.c
@@ -203,11 +203,12 @@ enum swrap_dbglvl_e {
 #define SOCKET_TYPE_CHAR_UDP_V6                'Y'
 
 /*
- * Cut down to 1500 byte packets for stream sockets,
- * which makes it easier to format PCAP capture files
- * (as the caller will simply continue from here)
+ * Set the packet MTU to 1500 bytes for stream sockets to make it it easier to
+ * format PCAP capture files (as the caller will simply continue from here).
  */
-#define SOCKET_MAX_PACKET 1500
+#define SOCKET_WRAPPER_MTU_DEFAULT 1500
+#define SOCKET_WRAPPER_MTU_MIN     512
+#define SOCKET_WRAPPER_MTU_MAX     32768
 
 #define SOCKET_MAX_SOCKETS 1024
 
@@ -912,6 +913,38 @@ static const char *socket_wrapper_dir(void)
        return s;
 }
 
+static unsigned int socket_wrapper_mtu(void)
+{
+       static unsigned int max_mtu = 0;
+       unsigned int tmp;
+       const char *s;
+       char *endp;
+
+       if (max_mtu != 0) {
+               return max_mtu;
+       }
+
+       max_mtu = SOCKET_WRAPPER_MTU_DEFAULT;
+
+       s = getenv("SOCKET_WRAPPER_MTU");
+       if (s == NULL) {
+               goto done;
+       }
+
+       tmp = strtol(s, &endp, 10);
+       if (s == endp) {
+               goto done;
+       }
+
+       if (tmp < SOCKET_WRAPPER_MTU_MIN || tmp > SOCKET_WRAPPER_MTU_MAX) {
+               goto done;
+       }
+       max_mtu = tmp;
+
+done:
+       return max_mtu;
+}
+
 bool socket_wrapper_enabled(void)
 {
        const char *s = socket_wrapper_dir();
@@ -3743,7 +3776,9 @@ static ssize_t swrap_sendmsg_before(int fd,
        }
 
        switch (si->type) {
-       case SOCK_STREAM:
+       case SOCK_STREAM: {
+               unsigned long mtu;
+
                if (!si->connected) {
                        errno = ENOTCONN;
                        return -1;
@@ -3753,22 +3788,23 @@ static ssize_t swrap_sendmsg_before(int fd,
                        break;
                }
 
+               mtu = socket_wrapper_mtu();
                for (i = 0; i < (size_t)msg->msg_iovlen; i++) {
                        size_t nlen;
                        nlen = len + msg->msg_iov[i].iov_len;
-                       if (nlen > SOCKET_MAX_PACKET) {
+                       if (nlen > mtu) {
                                break;
                        }
                }
                msg->msg_iovlen = i;
                if (msg->msg_iovlen == 0) {
                        *tmp_iov = msg->msg_iov[0];
-                       tmp_iov->iov_len = MIN(tmp_iov->iov_len, SOCKET_MAX_PACKET);
+                       tmp_iov->iov_len = MIN(tmp_iov->iov_len, mtu);
                        msg->msg_iov = tmp_iov;
                        msg->msg_iovlen = 1;
                }
                break;
-
+       }
        case SOCK_DGRAM:
                if (si->connected) {
                        if (msg->msg_name) {
@@ -3958,7 +3994,8 @@ static int swrap_recvmsg_before(int fd,
        (void)fd; /* unused */
 
        switch (si->type) {
-       case SOCK_STREAM:
+       case SOCK_STREAM: {
+               unsigned int mtu;
                if (!si->connected) {
                        errno = ENOTCONN;
                        return -1;
@@ -3968,22 +4005,23 @@ static int swrap_recvmsg_before(int fd,
                        break;
                }
 
+               mtu = socket_wrapper_mtu();
                for (i = 0; i < (size_t)msg->msg_iovlen; i++) {
                        size_t nlen;
                        nlen = len + msg->msg_iov[i].iov_len;
-                       if (nlen > SOCKET_MAX_PACKET) {
+                       if (nlen > mtu) {
                                break;
                        }
                }
                msg->msg_iovlen = i;
                if (msg->msg_iovlen == 0) {
                        *tmp_iov = msg->msg_iov[0];
-                       tmp_iov->iov_len = MIN(tmp_iov->iov_len, SOCKET_MAX_PACKET);
+                       tmp_iov->iov_len = MIN(tmp_iov->iov_len, mtu);
                        msg->msg_iov = tmp_iov;
                        msg->msg_iovlen = 1;
                }
                break;
-
+       }
        case SOCK_DGRAM:
                if (msg->msg_name == NULL) {
                        errno = EINVAL;