nbd: Share common option-sending code in client

Rather than open-coding each option request, it's easier to
have common helper functions do the work.  That in turn requires
having convenient packed types for handling option requests
and replies.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1476469998-28592-9-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 22 insertions, 3 deletions

diff --git a/include/block/nbd.h b/include/block/nbd.h
index a33581b6a9..b69bf1dc68 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -26,15 +26,34 @@
 #include "io/channel-socket.h"
 #include "crypto/tlscreds.h"
 
-/* Note: these are _NOT_ the same as the network representation of an NBD
+/* Handshake phase structs - this struct is passed on the wire */
+
+struct nbd_option {
+    uint64_t magic; /* NBD_OPTS_MAGIC */
+    uint32_t option; /* NBD_OPT_* */
+    uint32_t length;
+} QEMU_PACKED;
+typedef struct nbd_option nbd_option;
+
+struct nbd_opt_reply {
+    uint64_t magic; /* NBD_REP_MAGIC */
+    uint32_t option; /* NBD_OPT_* */
+    uint32_t type; /* NBD_REP_* */
+    uint32_t length;
+} QEMU_PACKED;
+typedef struct nbd_opt_reply nbd_opt_reply;
+
+/* Transmission phase structs
+ *
+ * Note: these are _NOT_ the same as the network representation of an NBD
  * request and reply!
  */
 struct NBDRequest {
     uint64_t handle;
     uint64_t from;
     uint32_t len;
-    uint16_t flags;
-    uint16_t type;
+    uint16_t flags; /* NBD_CMD_FLAG_* */
+    uint16_t type; /* NBD_CMD_* */
 };
 typedef struct NBDRequest NBDRequest;