Hacking away at stuff. Pretty soon there should be a working prototype.

Makefile

@@ -8,10 +8,10 @@ LDFLAGS	:=
 .PHONY: all clean
 all: $(TARGET)
 
-$(TARGET): $(OBJS) abuse.h
+$(TARGET): $(OBJS)
 	$(CC) $(LDFLAGS) -o $@ $^
 
-$(OBJS): %.o: %.c
+$(OBJS): %.o: %.c abuse.h
 	$(CC) $(CFLAGS) -o $@ -c $<
 
 clean:

abuse.c

@@ -1,4 +1,58 @@
-int abuse_main()
+#include <assert.h>
+#include <fcntl.h>
+#include <linux/types.h>
+#include <nbd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "abuse.h"
+
+int abuse_main(int argc, char *argv[], struct abuse_operations *aop)
 {
+    int sp[2];
+    int nbd, sk, err, tmp_fd;
+    char *dev_file;
+
+    assert(argc == 2);
+    dev_file = argv[1];
+
+    assert(!socketpair(AF_UNIX, SOCK_STREAM, 0, sp));
+
+    nbd = open(dev_file, O_RDWR);
+    assert(nbd != -1);
+
+    assert(ioctl(nbd, NBD_SET_SIZE, aop->size) != -1);
+    assert(ioctl(nbd, NBD_CLEAR_SOCK) != -1);
+
+    if (!fork()) {
+        /* The child needs to continue setting things up. */
+        close(sp[0]);
+        sk = sp[1];
+
+        assert(ioctl(nbd, NBD_SET_SOCK, sk) != -1);
+        err = ioctl(nbd, NBD_DO_IT);
+        fprintf(stderr, "nbd device terminated with code %d\n", err);
+
+        assert(ioctl(nbd, NBD_CLEAR_QUE) != -1);
+        assert(ioctl(nbd, NBD_CLEAR_SOCK) != -1);
+
+        exit(0);
+    }
+
+    /* The parent opens the device file at least once, to make sure the
+     * partition table is updated. Then it closes it and starts serving up
+     * requests. */
+
+    tmp_fd = open(dev_file, O_RDONLY);
+    assert(tmp_fd != -1);
+    close(tmp_fd);
+
+    close(sp[1]);
+    sk = sp[0];
+
     return 0;
 }

abuse.h

@@ -1,14 +1,18 @@
 #ifndef ABUSE_H_INCLUDED
 #define ABUSE_H_INCLUDED
 
+#include <sys/types.h>
+
 struct abuse_operations {
     void (*read)();
     void (*write)();
     void (*disc)();
     void (*flush)();
     void (*trim)();
+
+    u_int64_t size;
 };
 
-int abuse_main();
+int abuse_main(int argc, char *argv[], struct abuse_operations *aop);
 
 #endif /* ABUSE_H_INCLUDED */

abuse_example.c

@@ -1,6 +1,8 @@
+#include <stdlib.h>
+
 #include "abuse.h"
 
-int main()
+int main(int argc, char *argv[])
 {
-    return abuse_main();
+    return abuse_main(argc, argv, NULL);
 }