nbd: Consistent typedef usage in header

We had a mix of struct declarations followed by typedefs, and direct
struct definitions as part of a typedef.  Pick a single style.  Also
float forward declarations of opaque types to the top of the file,
rather than interspersed with function declarations, which will help a
future patch that wants to expose yet another opaque type that will be
referenced in NBDRequest.  No semantic impact.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20230608135653.2918540-3-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
[eblake: alter patch per mailing list feedback]
Signed-off-by: Eric Blake <eblake@redhat.com>

include/block/nbd.h

@@ -1,5 +1,5 @@
 /*
- *  Copyright (C) 2016-2022 Red Hat, Inc.
+ *  Copyright Red Hat
  *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
  *
  *  Network Block Device
@@ -26,24 +26,26 @@
 #include "qapi/error.h"
 #include "qemu/bswap.h"
 
+typedef struct NBDExport NBDExport;
+typedef struct NBDClient NBDClient;
+typedef struct NBDClientConnection NBDClientConnection;
+
 extern const BlockExportDriver blk_exp_nbd;
 
 /* Handshake phase structs - this struct is passed on the wire */
 
-struct NBDOption {
+typedef struct NBDOption {
     uint64_t magic; /* NBD_OPTS_MAGIC */
     uint32_t option; /* NBD_OPT_* */
     uint32_t length;
-} QEMU_PACKED;
-typedef struct NBDOption NBDOption;
+} QEMU_PACKED NBDOption;
 
-struct NBDOptionReply {
+typedef struct NBDOptionReply {
     uint64_t magic; /* NBD_REP_MAGIC */
     uint32_t option; /* NBD_OPT_* */
     uint32_t type; /* NBD_REP_* */
     uint32_t length;
-} QEMU_PACKED;
-typedef struct NBDOptionReply NBDOptionReply;
+} QEMU_PACKED NBDOptionReply;
 
 typedef struct NBDOptionReplyMetaContext {
     NBDOptionReply h; /* h.type = NBD_REP_META_CONTEXT, h.length > 4 */
@@ -56,14 +58,13 @@ typedef struct NBDOptionReplyMetaContext {
  * Note: these are _NOT_ the same as the network representation of an NBD
  * request and reply!
  */
-struct NBDRequest {
+typedef struct NBDRequest {
     uint64_t handle;
     uint64_t from;
     uint32_t len;
     uint16_t flags; /* NBD_CMD_FLAG_* */
     uint16_t type; /* NBD_CMD_* */
-};
-typedef struct NBDRequest NBDRequest;
+} NBDRequest;
 
 typedef struct NBDSimpleReply {
     uint32_t magic;  /* NBD_SIMPLE_REPLY_MAGIC */
@@ -282,7 +283,7 @@ static inline bool nbd_reply_type_is_error(int type)
 #define NBD_ESHUTDOWN  108
 
 /* Details collected by NBD_OPT_EXPORT_NAME and NBD_OPT_GO */
-struct NBDExportInfo {
+typedef struct NBDExportInfo {
     /* Set by client before nbd_receive_negotiate() */
     bool request_sizes;
     char *x_dirty_bitmap;
@@ -310,8 +311,7 @@ struct NBDExportInfo {
     char *description;
     int n_contexts;
     char **contexts;
-};
-typedef struct NBDExportInfo NBDExportInfo;
+} NBDExportInfo;
 
 int nbd_receive_negotiate(AioContext *aio_context, QIOChannel *ioc,
                           QCryptoTLSCreds *tlscreds,
@@ -330,9 +330,6 @@ int nbd_client(int fd);
 int nbd_disconnect(int fd);
 int nbd_errno_to_system_errno(int err);
 
-typedef struct NBDExport NBDExport;
-typedef struct NBDClient NBDClient;
-
 void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk);
 
 AioContext *nbd_export_aio_context(NBDExport *exp);
@@ -409,8 +406,6 @@ const char *nbd_cmd_lookup(uint16_t info);
 const char *nbd_err_lookup(int err);
 
 /* nbd/client-connection.c */
-typedef struct NBDClientConnection NBDClientConnection;
-
 void nbd_client_connection_enable_retry(NBDClientConnection *conn);
 
 NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,