nbd/client: Initial support for extended headers

Update the client code to be able to send an extended request, and
parse an extended header from the server.  Note that since we reject
any structured reply with a too-large payload, we can always normalize
a valid header back into the compact form, so that the caller need not
deal with two branches of a union.  Still, until a later patch lets
the client negotiate extended headers, the code added here should not
be reached.  Note that because of the different magic numbers, it is
just as easy to trace and then tolerate a non-compliant server sending
the wrong header reply as it would be to insist that the server is
compliant.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20230925192229.3186470-21-eblake@redhat.com>
[eblake: fix trace format]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>

block/nbd.c

@@ -458,7 +458,7 @@ static coroutine_fn int nbd_receive_replies(BDRVNBDState *s, uint64_t cookie,
 
         /* We are under mutex and cookie is 0. We have to do the dirty work. */
         assert(s->reply.cookie == 0);
-        ret = nbd_receive_reply(s->bs, s->ioc, &s->reply, errp);
+        ret = nbd_receive_reply(s->bs, s->ioc, &s->reply, s->info.mode, errp);
         if (ret == 0) {
             ret = -EIO;
             error_setg(errp, "server dropped connection");

include/block/nbd.h

@@ -389,7 +389,8 @@ int nbd_init(int fd, QIOChannelSocket *sioc, NBDExportInfo *info,
              Error **errp);
 int nbd_send_request(QIOChannel *ioc, NBDRequest *request);
 int coroutine_fn nbd_receive_reply(BlockDriverState *bs, QIOChannel *ioc,
-                                   NBDReply *reply, Error **errp);
+                                   NBDReply *reply, NBDMode mode,
+                                   Error **errp);
 int nbd_client(int fd);
 int nbd_disconnect(int fd);
 int nbd_errno_to_system_errno(int err);

nbd/client.c

@@ -1346,22 +1346,29 @@ int nbd_disconnect(int fd)
 
 int nbd_send_request(QIOChannel *ioc, NBDRequest *request)
 {
-    uint8_t buf[NBD_REQUEST_SIZE];
+    uint8_t buf[NBD_EXTENDED_REQUEST_SIZE];
+    size_t len;
 
-    assert(request->mode <= NBD_MODE_STRUCTURED); /* TODO handle extended */
-    assert(request->len <= UINT32_MAX);
     trace_nbd_send_request(request->from, request->len, request->cookie,
                            request->flags, request->type,
                            nbd_cmd_lookup(request->type));
 
-    stl_be_p(buf, NBD_REQUEST_MAGIC);
     stw_be_p(buf + 4, request->flags);
     stw_be_p(buf + 6, request->type);
     stq_be_p(buf + 8, request->cookie);
     stq_be_p(buf + 16, request->from);
-    stl_be_p(buf + 24, request->len);
+    if (request->mode >= NBD_MODE_EXTENDED) {
+        stl_be_p(buf, NBD_EXTENDED_REQUEST_MAGIC);
+        stq_be_p(buf + 24, request->len);
+        len = NBD_EXTENDED_REQUEST_SIZE;
+    } else {
+        assert(request->len <= UINT32_MAX);
+        stl_be_p(buf, NBD_REQUEST_MAGIC);
+        stl_be_p(buf + 24, request->len);
+        len = NBD_REQUEST_SIZE;
+    }
 
-    return nbd_write(ioc, buf, sizeof(buf), NULL);
+    return nbd_write(ioc, buf, len, NULL);
 }
 
 /* nbd_receive_simple_reply
@@ -1388,30 +1395,36 @@ static int nbd_receive_simple_reply(QIOChannel *ioc, NBDSimpleReply *reply,
     return 0;
 }
 
-/* nbd_receive_structured_reply_chunk
+/* nbd_receive_reply_chunk_header
  * Read structured reply chunk except magic field (which should be already
- * read).
+ * read).  Normalize into the compact form.
  * Payload is not read.
  */
-static int nbd_receive_structured_reply_chunk(QIOChannel *ioc,
-                                              NBDStructuredReplyChunk *chunk,
-                                              Error **errp)
+static int nbd_receive_reply_chunk_header(QIOChannel *ioc, NBDReply *chunk,
+                                          Error **errp)
 {
     int ret;
+    size_t len;
+    uint64_t payload_len;
 
-    assert(chunk->magic == NBD_STRUCTURED_REPLY_MAGIC);
+    if (chunk->magic == NBD_STRUCTURED_REPLY_MAGIC) {
+        len = sizeof(chunk->structured);
+    } else {
+        assert(chunk->magic == NBD_EXTENDED_REPLY_MAGIC);
+        len = sizeof(chunk->extended);
+    }
 
     ret = nbd_read(ioc, (uint8_t *)chunk + sizeof(chunk->magic),
-                   sizeof(*chunk) - sizeof(chunk->magic), "structured chunk",
+                   len - sizeof(chunk->magic), "structured chunk",
                    errp);
     if (ret < 0) {
         return ret;
     }
 
-    chunk->flags = be16_to_cpu(chunk->flags);
-    chunk->type = be16_to_cpu(chunk->type);
-    chunk->cookie = be64_to_cpu(chunk->cookie);
-    chunk->length = be32_to_cpu(chunk->length);
+    /* flags, type, and cookie occupy same space between forms */
+    chunk->structured.flags = be16_to_cpu(chunk->structured.flags);
+    chunk->structured.type = be16_to_cpu(chunk->structured.type);
+    chunk->structured.cookie = be64_to_cpu(chunk->structured.cookie);
 
     /*
      * Because we use BLOCK_STATUS with REQ_ONE, and cap READ requests
@@ -1419,11 +1432,20 @@ static int nbd_receive_structured_reply_chunk(QIOChannel *ioc,
      * this.  Even if we stopped using REQ_ONE, sane servers will cap
      * the number of extents they return for block status.
      */
-    if (chunk->length > NBD_MAX_BUFFER_SIZE + sizeof(NBDStructuredReadData)) {
+    if (chunk->magic == NBD_STRUCTURED_REPLY_MAGIC) {
+        payload_len = be32_to_cpu(chunk->structured.length);
+    } else {
+        /* For now, we are ignoring the extended header offset. */
+        payload_len = be64_to_cpu(chunk->extended.length);
+        chunk->magic = NBD_STRUCTURED_REPLY_MAGIC;
+    }
+    if (payload_len > NBD_MAX_BUFFER_SIZE + sizeof(NBDStructuredReadData)) {
         error_setg(errp, "server chunk %" PRIu32 " (%s) payload is too long",
-                   chunk->type, nbd_rep_lookup(chunk->type));
+                   chunk->structured.type,
+                   nbd_rep_lookup(chunk->structured.type));
         return -EINVAL;
     }
+    chunk->structured.length = payload_len;
 
     return 0;
 }
@@ -1470,19 +1492,21 @@ nbd_read_eof(BlockDriverState *bs, QIOChannel *ioc, void *buffer, size_t size,
 
 /* nbd_receive_reply
  *
- * Decreases bs->in_flight while waiting for a new reply. This yield is where
- * we wait indefinitely and the coroutine must be able to be safely reentered
- * for nbd_client_attach_aio_context().
+ * Wait for a new reply. If this yields, the coroutine must be able to be
+ * safely reentered for nbd_client_attach_aio_context().  @mode determines
+ * which reply magic we are expecting, although this normalizes the result
+ * so that the caller only has to work with compact headers.
  *
  * Returns 1 on success
- *         0 on eof, when no data was read (errp is not set)
- *         negative errno on failure (errp is set)
+ *         0 on eof, when no data was read
+ *         negative errno on failure
  */
 int coroutine_fn nbd_receive_reply(BlockDriverState *bs, QIOChannel *ioc,
-                                   NBDReply *reply, Error **errp)
+                                   NBDReply *reply, NBDMode mode, Error **errp)
 {
     int ret;
     const char *type;
+    uint32_t expected;
 
     ret = nbd_read_eof(bs, ioc, &reply->magic, sizeof(reply->magic), errp);
     if (ret <= 0) {
@@ -1491,34 +1515,44 @@ int coroutine_fn nbd_receive_reply(BlockDriverState *bs, QIOChannel *ioc,
 
     reply->magic = be32_to_cpu(reply->magic);
 
+    /* Diagnose but accept wrong-width header */
     switch (reply->magic) {
     case NBD_SIMPLE_REPLY_MAGIC:
+        if (mode >= NBD_MODE_EXTENDED) {
+            trace_nbd_receive_wrong_header(reply->magic,
+                                           nbd_mode_lookup(mode));
+        }
         ret = nbd_receive_simple_reply(ioc, &reply->simple, errp);
         if (ret < 0) {
-            break;
+            return ret;
         }
         trace_nbd_receive_simple_reply(reply->simple.error,
                                        nbd_err_lookup(reply->simple.error),
                                        reply->cookie);
         break;
     case NBD_STRUCTURED_REPLY_MAGIC:
-        ret = nbd_receive_structured_reply_chunk(ioc, &reply->structured, errp);
+    case NBD_EXTENDED_REPLY_MAGIC:
+        expected = mode >= NBD_MODE_EXTENDED ? NBD_EXTENDED_REPLY_MAGIC
+            : NBD_STRUCTURED_REPLY_MAGIC;
+        if (reply->magic != expected) {
+            trace_nbd_receive_wrong_header(reply->magic,
+                                           nbd_mode_lookup(mode));
+        }
+        ret = nbd_receive_reply_chunk_header(ioc, reply, errp);
         if (ret < 0) {
-            break;
+            return ret;
         }
         type = nbd_reply_type_lookup(reply->structured.type);
-        trace_nbd_receive_structured_reply_chunk(reply->structured.flags,
-                                                 reply->structured.type, type,
-                                                 reply->structured.cookie,
-                                                 reply->structured.length);
+        trace_nbd_receive_reply_chunk_header(reply->structured.flags,
+                                             reply->structured.type, type,
+                                             reply->structured.cookie,
+                                             reply->structured.length);
         break;
     default:
+        trace_nbd_receive_wrong_header(reply->magic, nbd_mode_lookup(mode));
         error_setg(errp, "invalid magic (got 0x%" PRIx32 ")", reply->magic);
         return -EINVAL;
     }
-    if (ret < 0) {
-        return ret;
-    }
 
     return 1;
 }

nbd/trace-events

@@ -33,7 +33,8 @@ nbd_client_clear_queue(void) "Clearing NBD queue"
 nbd_client_clear_socket(void) "Clearing NBD socket"
 nbd_send_request(uint64_t from, uint64_t len, uint64_t cookie, uint16_t flags, uint16_t type, const char *name) "Sending request to server: { .from = %" PRIu64", .len = %" PRIu64 ", .cookie = %" PRIu64 ", .flags = 0x%" PRIx16 ", .type = %" PRIu16 " (%s) }"
 nbd_receive_simple_reply(int32_t error, const char *errname, uint64_t cookie) "Got simple reply: { .error = %" PRId32 " (%s), cookie = %" PRIu64" }"
-nbd_receive_structured_reply_chunk(uint16_t flags, uint16_t type, const char *name, uint64_t cookie, uint32_t length) "Got structured reply chunk: { flags = 0x%" PRIx16 ", type = %d (%s), cookie = %" PRIu64 ", length = %" PRIu32 " }"
+nbd_receive_reply_chunk_header(uint16_t flags, uint16_t type, const char *name, uint64_t cookie, uint32_t length) "Got reply chunk header: { flags = 0x%" PRIx16 ", type = %" PRIu16 " (%s), cookie = %" PRIu64 ", length = %" PRIu32 " }"
+nbd_receive_wrong_header(uint32_t magic, const char *mode) "Server sent unexpected magic 0x%" PRIx32 " for negotiated mode %s"
 
 # common.c
 nbd_unknown_error(int err) "Squashing unexpected error %d to EINVAL"