diff --git a/io/iob_prefetch.c b/io/iob_prefetch.c
new file mode 100644
index 0000000..1f40b83
--- /dev/null
+++ b/io/iob_prefetch.c
@@ -0,0 +1,29 @@
+#include "iob_internal.h"
+#include <stdio.h>
+#include <sys/mman.h>
+
+void iob_prefetch(io_batch* b,uint64 bytes) {
+  iob_entry* e,* last;
+  if (b->bytesleft==0) return;
+  last=(iob_entry*)(((char*)array_start(&b->b))+array_bytes(&b->b));
+  e=(iob_entry*)array_start(&b->b);
+  if (!e) return;
+  for (; e<last; ++e) {
+    if (e->type==FROMFILE) {
+      char* c,* d;
+      if (e->n>=1000000) {
+	d=c=mmap(0,bytes,PROT_READ,MAP_SHARED,e->fd,(e->offset|4095)+1);
+	if (c!=MAP_FAILED) {
+	  while (bytes>4096) {
+	    volatile char x=*d;
+	    bytes-=4096;
+	    d+=4096;
+	    (void)x;
+	  }
+	}
+	munmap(c,bytes);
+      }
+      return;
+    }
+  }
+}
diff --git a/io/iob_send.c b/io/iob_send.c
index ed3afc1..e09f39c 100644
--- a/io/iob_send.c
+++ b/io/iob_send.c
@@ -20,7 +20,7 @@ int64 iob_send(int64 s,io_batch* b) {
 #endif
 
   if (b->bytesleft==0) return 0;
-  last=((char*)array_start(&b->b))+array_bytes(&b->b);
+  last=(iob_entry*)(((char*)array_start(&b->b))+array_bytes(&b->b));
   v=alloca(b->bufs*sizeof(struct iovec));
   total=0;
   for (;;) {
@@ -114,6 +114,7 @@ eagain:
 	  if (!rest) break;
 	} else {
 	  e[i].offset+=rest;
+	  e[i].n-=rest;
 	  goto abort;
 	}
       }
diff --git a/iob.h b/iob.h
index 8bfb30a..0a46fa6 100644
--- a/iob.h
+++ b/iob.h
@@ -29,5 +29,6 @@ int iob_adds_free(io_batch* b,const char* s);
 int iob_addfile(io_batch* b,int64 fd,uint64 off,uint64 n);
 int64 iob_send(int64 s,io_batch* b);
 void iob_reset(io_batch* b);
+void iob_prefetch(io_batch* b,uint64 bytes);
 
 #endif
diff --git a/test/dnsip.c b/test/dnsip.c
index 0f7d6e0..6f01900 100644
--- a/test/dnsip.c
+++ b/test/dnsip.c
@@ -22,7 +22,7 @@ int main(int argc,char* argv[]) {
       buffer_puts(buffer_2,"unable to find IP address for ");
       buffer_puts(buffer_2,*argv);
       buffer_puts(buffer_2,": ");
-      buffer_puts(buffer_2,strerror(errno));
+      buffer_puterror(buffer_2);
       buffer_putnlflush(buffer_2);
       return 111;
     }