erts: Flatten too long io vectors in uds write

2 files changed, 36 insertions, 4 deletions

diff --git a/erts/emulator/sys/unix/sys_uds.c b/erts/emulator/sys/unix/sys_uds.c
index 3b63d05cf6..daebcb307b 100644
--- a/erts/emulator/sys/unix/sys_uds.c
+++ b/erts/emulator/sys/unix/sys_uds.c
@@ -18,7 +18,6 @@
  * %CopyrightEnd%
  */
 
-
 #include "sys_uds.h"
 
 int
@@ -89,12 +88,32 @@ sys_uds_writev(int fd, struct iovec *iov, size_t iov_len,
 
     struct msghdr msg;
     struct cmsghdr *cmsg = NULL;
-    int res;
+    int res, i;
 
     /* initialize socket message */
     memset(&msg, 0, sizeof(struct msghdr));
-    msg.msg_iov = iov;
-    msg.msg_iovlen = iov_len;
+
+    /* We flatten the iov if it is too long */
+    if (iov_len > MAXIOV) {
+        int size = 0;
+        char *buff;
+        for (i = 0; i < iov_len; i++)
+            size += iov[i].iov_len;
+        buff = malloc(size);
+
+        for (i = 0; i < iov_len; i++) {
+            memcpy(buff, iov[i].iov_base, iov[i].iov_len);
+            buff += iov[i].iov_len;
+        }
+
+        iov[0].iov_base = buff - size;
+        iov[0].iov_len = size;
+        msg.msg_iov = iov;
+        msg.msg_iovlen = 1;
+    } else {
+        msg.msg_iov = iov;
+        msg.msg_iovlen = iov_len;
+    }
 
     /* initialize the ancillary data */
     msg.msg_control = calloc(1, CMSG_SPACE(sizeof(int) * fd_count));
@@ -110,6 +129,9 @@ sys_uds_writev(int fd, struct iovec *iov, size_t iov_len,
 
     res = sendmsg(fd, &msg, flags);
 
+    if (iov_len > MAXIOV)
+        free(iov[0].iov_base);
+
     free(msg.msg_control);
 
     return res;
diff --git a/erts/emulator/sys/unix/sys_uds.h b/erts/emulator/sys/unix/sys_uds.h
index 7ff58b17dd..844a2804d8 100644
--- a/erts/emulator/sys/unix/sys_uds.h
+++ b/erts/emulator/sys/unix/sys_uds.h
@@ -29,10 +29,20 @@
 #define _XOPEN_SOURCE 500
 #endif
 
+#include <limits.h>
+
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/uio.h>
 
+#if defined IOV_MAX
+#define MAXIOV IOV_MAX
+#elif defined UIO_MAXIOV
+#define MAXIOV UIO_MAXIOV
+#else
+#define MAXIOV 16
+#endif
+
 #include "sys.h"
 
 int sys_uds_readv(int fd, struct iovec *iov, size_t iov_len,