Add linux user util support

This topic branch contains required changes to the user space
utilities to allow them to integrate cleanly with Linux.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

lib/libzfs/libzfs_sendrecv.c

@@ -34,6 +34,11 @@
 #include <stddef.h>
 #include <fcntl.h>
 #include <sys/mount.h>
+#include <sys/mntent.h>
+#include <sys/mnttab.h>
+#include <sys/avl.h>
+#include <sys/debug.h>
+#include <stddef.h>
 #include <pthread.h>
 #include <umem.h>
 

lib/libzfs/libzfs_util.c

@@ -614,6 +614,13 @@ libzfs_init(void)
 	}
 
 	if ((hdl->libzfs_fd = open(ZFS_DEV, O_RDWR)) < 0) {
+		(void) fprintf(stderr, gettext("Unable to open %s: %s.\n"),
+			       ZFS_DEV, strerror(errno));
+		if (errno == ENOENT)
+			(void) fprintf(stderr,
+			     gettext("Verify the ZFS module stack is "
+			     "loaded by running '/sbin/modprobe zfs'.\n"));
+
 		free(hdl);
 		return (NULL);
 	}