nbd: Fix struct name for structured reads

A closer read of the NBD spec shows that a structured reply chunk
for a hole is not quite identical to the prefix of a data chunk,
because the hole has to also send a 32-bit size field.  Although
we do not yet send holes, we should fix the misleading information
in our header and make it easier for a future patch to support
sparse reads.  Messed up in commit bae245d1.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20171108215703.9295-5-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 92d1723d7c..113c707a5e 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -86,15 +86,23 @@ typedef union NBDReply {
     } QEMU_PACKED;
 } NBDReply;
 
-/* Header of NBD_REPLY_TYPE_OFFSET_DATA, complete NBD_REPLY_TYPE_OFFSET_HOLE */
-typedef struct NBDStructuredRead {
-    NBDStructuredReplyChunk h;
+/* Header of chunk for NBD_REPLY_TYPE_OFFSET_DATA */
+typedef struct NBDStructuredReadData {
+    NBDStructuredReplyChunk h; /* h.length >= 9 */
     uint64_t offset;
-} QEMU_PACKED NBDStructuredRead;
+    /* At least one byte of data payload follows, calculated from h.length */
+} QEMU_PACKED NBDStructuredReadData;
+
+/* Complete chunk for NBD_REPLY_TYPE_OFFSET_HOLE */
+typedef struct NBDStructuredReadHole {
+    NBDStructuredReplyChunk h; /* h.length == 12 */
+    uint64_t offset;
+    uint32_t length;
+} QEMU_PACKED NBDStructuredReadHole;
 
 /* Header of all NBD_REPLY_TYPE_ERROR* errors */
 typedef struct NBDStructuredError {
-    NBDStructuredReplyChunk h;
+    NBDStructuredReplyChunk h; /* h.length >= 6 */
     uint32_t error;
     uint16_t message_length;
 } QEMU_PACKED NBDStructuredError;