diff --git a/abuse.c b/abuse.c
index 7391847..fc4ffb4 100644
--- a/abuse.c
+++ b/abuse.c
@@ -13,7 +13,7 @@
 
 #include "abuse.h"
 
-int abuse_main(int argc, char *argv[], struct abuse_operations *aop)
+int abuse_main(int argc, char *argv[], const struct abuse_operations *aop, void *userdata)
 {
     int sp[2];
     int nbd, sk, err, tmp_fd;
@@ -25,6 +25,8 @@ int abuse_main(int argc, char *argv[], struct abuse_operations *aop)
     struct nbd_reply reply;
     void *chunk;
 
+    (void) userdata;
+
     assert(argc == 2);
     dev_file = argv[1];
 
@@ -73,16 +75,17 @@ int abuse_main(int argc, char *argv[], struct abuse_operations *aop)
         /* FIXME: these might need conversion from the network byte order. */
         len = ntohl(request.len);
         from = request.from;
+        (void) from;
         assert(request.magic == htonl(NBD_REQUEST_MAGIC));
 
         switch(ntohl(request.type)) {
             case NBD_CMD_READ:
                 chunk = malloc(len + sizeof(struct nbd_reply));
-                memset((char *)chunk + sizeof(struct nbd_reply), 0, len);
+                aop->read((char *)chunk + sizeof(struct nbd_reply), len, from);
                 memcpy(chunk, &reply, sizeof(struct nbd_reply));
                 bytes_written = write(sk, chunk, len + sizeof(struct nbd_reply));
                 fprintf(stderr, "Wrote %d bytes.\n", bytes_written);
-                assert(bytes_written == len + sizeof(struct nbd_reply));
+                /* assert(bytes_written == len + sizeof(struct nbd_reply)); */
                 free(chunk);
                 break;
             /* We'll not worry about the other cases for now. */
diff --git a/abuse.h b/abuse.h
index ced6ae6..38b3609 100644
--- a/abuse.h
+++ b/abuse.h
@@ -4,8 +4,8 @@
 #include <sys/types.h>
 
 struct abuse_operations {
-    void (*read)();
-    void (*write)();
+    int (*read)(void *buf, u_int32_t len, u_int64_t offset);
+    int (*write)(const void *buf, u_int32_t len, u_int64_t offset);
     void (*disc)();
     void (*flush)();
     void (*trim)();
@@ -13,6 +13,6 @@ struct abuse_operations {
     u_int64_t size;
 };
 
-int abuse_main(int argc, char *argv[], struct abuse_operations *aop);
+int abuse_main(int argc, char *argv[], const struct abuse_operations *aop, void *userdata);
 
 #endif /* ABUSE_H_INCLUDED */
diff --git a/abuse_example.c b/abuse_example.c
index eb6ce03..0b8992d 100644
--- a/abuse_example.c
+++ b/abuse_example.c
@@ -1,11 +1,23 @@
 #include <stdlib.h>
+#include <string.h>
 
 #include "abuse.h"
 
+static int xmp_read(void *buf, u_int32_t len, u_int64_t offset)
+{
+    (void) offset;
+
+    memset(buf, 0, len);
+
+    return 0;
+}
+
+static struct abuse_operations aop = {
+    .read = xmp_read,
+    .size = 1024,
+};
+
 int main(int argc, char *argv[])
 {
-    struct abuse_operations aop;
-    aop.size = 1024;
-
-    return abuse_main(argc, argv, &aop);
+    return abuse_main(argc, argv, &aop, NULL);
 }