nbd: Treat flags vs. command type as separate fields

Current upstream NBD documents that requests have a 16-bit flags,
followed by a 16-bit type integer; although older versions mentioned
only a 32-bit field with masking to find flags.  Since the protocol
is in network order (big-endian over the wire), the ABI is unchanged;
but dealing with the flags as a separate field rather than masking
will make it easier to add support for upcoming NBD extensions that
increase the number of both flags and commands.

Improve some comments in nbd.h based on the current upstream
NBD protocol (https://github.com/yoe/nbd/blob/master/doc/proto.md),
and touch some nearby code to keep checkpatch.pl happy.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1476469998-28592-3-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

5 files changed, 42 insertions, 37 deletions

diff --git a/block/nbd-client.c b/block/nbd-client.c
index 40b28ab00b..8ca503015c 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -1,6 +1,7 @@
 /*
  * QEMU Block driver for  NBD
  *
+ * Copyright (C) 2016 Red Hat, Inc.
  * Copyright (C) 2008 Bull S.A.S.
  *     Author: Laurent Vivier <Laurent.Vivier@bull.net>
  *
@@ -258,7 +259,7 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
 
     if (flags & BDRV_REQ_FUA) {
         assert(client->nbdflags & NBD_FLAG_SEND_FUA);
-        request.type |= NBD_CMD_FLAG_FUA;
+        request.flags |= NBD_CMD_FLAG_FUA;
     }
 
     assert(bytes <= NBD_MAX_BUFFER_SIZE);
@@ -343,11 +344,7 @@ void nbd_client_attach_aio_context(BlockDriverState *bs,
 void nbd_client_close(BlockDriverState *bs)
 {
     NbdClientSession *client = nbd_get_client_session(bs);
-    struct nbd_request request = {
-        .type = NBD_CMD_DISC,
-        .from = 0,
-        .len = 0
-    };
+    struct nbd_request request = { .type = NBD_CMD_DISC };
 
     if (client->ioc == NULL) {
         return;
diff --git a/include/block/nbd.h b/include/block/nbd.h
index fd58390d5d..5fe2670fdb 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -1,4 +1,5 @@
 /*
+ *  Copyright (C) 2016 Red Hat, Inc.
  *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
  *
  *  Network Block Device
@@ -32,7 +33,8 @@ struct nbd_request {
     uint64_t handle;
     uint64_t from;
     uint32_t len;
-    uint32_t type;
+    uint16_t flags;
+    uint16_t type;
 };
 
 struct nbd_reply {
@@ -40,6 +42,8 @@ struct nbd_reply {
     uint32_t error;
 };
 
+/* Transmission (export) flags: sent from server to client during handshake,
+   but describe what will happen during transmission */
 #define NBD_FLAG_HAS_FLAGS      (1 << 0)        /* Flags are there */
 #define NBD_FLAG_READ_ONLY      (1 << 1)        /* Device is read-only */
 #define NBD_FLAG_SEND_FLUSH     (1 << 2)        /* Send FLUSH */
@@ -47,10 +51,12 @@ struct nbd_reply {
 #define NBD_FLAG_ROTATIONAL     (1 << 4)        /* Use elevator algorithm - rotational media */
 #define NBD_FLAG_SEND_TRIM      (1 << 5)        /* Send TRIM (discard) */
 
-/* New-style global flags. */
+/* New-style handshake (global) flags, sent from server to client, and
+   control what will happen during handshake phase. */
 #define NBD_FLAG_FIXED_NEWSTYLE     (1 << 0)    /* Fixed newstyle protocol. */
 
-/* New-style client flags. */
+/* New-style client flags, sent from client to server to control what happens
+   during handshake phase. */
 #define NBD_FLAG_C_FIXED_NEWSTYLE   (1 << 0)    /* Fixed newstyle protocol. */
 
 /* Reply types. */
@@ -61,10 +67,10 @@ struct nbd_reply {
 #define NBD_REP_ERR_INVALID     ((UINT32_C(1) << 31) | 3) /* Invalid length. */
 #define NBD_REP_ERR_TLS_REQD    ((UINT32_C(1) << 31) | 5) /* TLS required */
 
+/* Request flags, sent from client to server during transmission phase */
+#define NBD_CMD_FLAG_FUA        (1 << 0)
 
-#define NBD_CMD_MASK_COMMAND	0x0000ffff
-#define NBD_CMD_FLAG_FUA	(1 << 16)
-
+/* Supported request types */
 enum {
     NBD_CMD_READ = 0,
     NBD_CMD_WRITE = 1,
diff --git a/nbd/client.c b/nbd/client.c
index f6db8369b3..4620e8dcba 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -1,4 +1,5 @@
 /*
+ *  Copyright (C) 2016 Red Hat, Inc.
  *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
  *
  *  Network Block Device Client Side
@@ -714,11 +715,13 @@ ssize_t nbd_send_request(QIOChannel *ioc, struct nbd_request *request)
 
     TRACE("Sending request to server: "
           "{ .from = %" PRIu64", .len = %" PRIu32 ", .handle = %" PRIu64
-          ", .type=%" PRIu32 " }",
-          request->from, request->len, request->handle, request->type);
+          ", .flags = %" PRIx16 ", .type = %" PRIu16 " }",
+          request->from, request->len, request->handle,
+          request->flags, request->type);
 
     stl_be_p(buf, NBD_REQUEST_MAGIC);
-    stl_be_p(buf + 4, request->type);
+    stw_be_p(buf + 4, request->flags);
+    stw_be_p(buf + 6, request->type);
     stq_be_p(buf + 8, request->handle);
     stq_be_p(buf + 16, request->from);
     stl_be_p(buf + 24, request->len);
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index 7e78064021..99e51571a2 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -53,10 +53,10 @@
 /* This is all part of the "official" NBD API.
  *
  * The most up-to-date documentation is available at:
- * https://github.com/yoe/nbd/blob/master/doc/proto.txt
+ * https://github.com/yoe/nbd/blob/master/doc/proto.md
  */
 
-#define NBD_REQUEST_SIZE        (4 + 4 + 8 + 8 + 4)
+#define NBD_REQUEST_SIZE        (4 + 2 + 2 + 8 + 8 + 4)
 #define NBD_REPLY_SIZE          (4 + 4 + 8)
 #define NBD_REQUEST_MAGIC       0x25609513
 #define NBD_REPLY_MAGIC         0x67446698
diff --git a/nbd/server.c b/nbd/server.c
index ac42391b45..38a0fef4d9 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1,4 +1,5 @@
 /*
+ *  Copyright (C) 2016 Red Hat, Inc.
  *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
  *
  *  Network Block Device Server Side
@@ -652,21 +653,23 @@ static ssize_t nbd_receive_request(QIOChannel *ioc, struct nbd_request *request)
 
     /* Request
        [ 0 ..  3]   magic   (NBD_REQUEST_MAGIC)
-       [ 4 ..  7]   type    (0 == READ, 1 == WRITE)
+       [ 4 ..  5]   flags   (NBD_CMD_FLAG_FUA, ...)
+       [ 6 ..  7]   type    (NBD_CMD_READ, ...)
        [ 8 .. 15]   handle
        [16 .. 23]   from
        [24 .. 27]   len
      */
 
     magic = ldl_be_p(buf);
-    request->type   = ldl_be_p(buf + 4);
+    request->flags  = lduw_be_p(buf + 4);
+    request->type   = lduw_be_p(buf + 6);
     request->handle = ldq_be_p(buf + 8);
     request->from   = ldq_be_p(buf + 16);
     request->len    = ldl_be_p(buf + 24);
 
-    TRACE("Got request: { magic = 0x%" PRIx32 ", .type = %" PRIx32
-          ", from = %" PRIu64 " , len = %" PRIu32 " }",
-          magic, request->type, request->from, request->len);
+    TRACE("Got request: { magic = 0x%" PRIx32 ", .flags = %" PRIx16
+          ", .type = %" PRIx16 ", from = %" PRIu64 ", len = %" PRIu32 " }",
+          magic, request->flags, request->type, request->from, request->len);
 
     if (magic != NBD_REQUEST_MAGIC) {
         LOG("invalid magic (got 0x%" PRIx32 ")", magic);
@@ -1013,7 +1016,6 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
                                       struct nbd_request *request)
 {
     NBDClient *client = req->client;
-    uint32_t command;
     ssize_t rc;
 
     g_assert(qemu_in_coroutine());
@@ -1030,13 +1032,12 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
 
     TRACE("Decoding type");
 
-    command = request->type & NBD_CMD_MASK_COMMAND;
-    if (command != NBD_CMD_WRITE) {
+    if (request->type != NBD_CMD_WRITE) {
         /* No payload, we are ready to read the next request.  */
         req->complete = true;
     }
 
-    if (command == NBD_CMD_DISC) {
+    if (request->type == NBD_CMD_DISC) {
         /* Special case: we're going to disconnect without a reply,
          * whether or not flags, from, or len are bogus */
         TRACE("Request type is DISCONNECT");
@@ -1053,7 +1054,7 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
         goto out;
     }
 
-    if (command == NBD_CMD_READ || command == NBD_CMD_WRITE) {
+    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE) {
         if (request->len > NBD_MAX_BUFFER_SIZE) {
             LOG("len (%" PRIu32" ) is larger than max len (%u)",
                 request->len, NBD_MAX_BUFFER_SIZE);
@@ -1067,7 +1068,7 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
             goto out;
         }
     }
-    if (command == NBD_CMD_WRITE) {
+    if (request->type == NBD_CMD_WRITE) {
         TRACE("Reading %" PRIu32 " byte(s)", request->len);
 
         if (read_sync(client->ioc, req->data, request->len) != request->len) {
@@ -1083,12 +1084,11 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
         LOG("operation past EOF; From: %" PRIu64 ", Len: %" PRIu32
             ", Size: %" PRIu64, request->from, request->len,
             (uint64_t)client->exp->size);
-        rc = command == NBD_CMD_WRITE ? -ENOSPC : -EINVAL;
+        rc = request->type == NBD_CMD_WRITE ? -ENOSPC : -EINVAL;
         goto out;
     }
-    if (request->type & ~NBD_CMD_MASK_COMMAND & ~NBD_CMD_FLAG_FUA) {
-        LOG("unsupported flags (got 0x%x)",
-            request->type & ~NBD_CMD_MASK_COMMAND);
+    if (request->flags & ~NBD_CMD_FLAG_FUA) {
+        LOG("unsupported flags (got 0x%x)", request->flags);
         rc = -EINVAL;
         goto out;
     }
@@ -1110,7 +1110,6 @@ static void nbd_trip(void *opaque)
     struct nbd_request request;
     struct nbd_reply reply;
     ssize_t ret;
-    uint32_t command;
     int flags;
 
     TRACE("Reading request.");
@@ -1134,7 +1133,6 @@ static void nbd_trip(void *opaque)
         reply.error = -ret;
         goto error_reply;
     }
-    command = request.type & NBD_CMD_MASK_COMMAND;
 
     if (client->closing) {
         /*
@@ -1144,11 +1142,12 @@ static void nbd_trip(void *opaque)
         goto done;
     }
 
-    switch (command) {
+    switch (request.type) {
     case NBD_CMD_READ:
         TRACE("Request type is READ");
 
-        if (request.type & NBD_CMD_FLAG_FUA) {
+        /* XXX: NBD Protocol only documents use of FUA with WRITE */
+        if (request.flags & NBD_CMD_FLAG_FUA) {
             ret = blk_co_flush(exp->blk);
             if (ret < 0) {
                 LOG("flush failed");
@@ -1181,7 +1180,7 @@ static void nbd_trip(void *opaque)
         TRACE("Writing to device");
 
         flags = 0;
-        if (request.type & NBD_CMD_FLAG_FUA) {
+        if (request.flags & NBD_CMD_FLAG_FUA) {
             flags |= BDRV_REQ_FUA;
         }
         ret = blk_pwrite(exp->blk, request.from + exp->dev_offset,