Re: [Libguestfs] [PATCH v7 12/12] nbd/server: Add FLAG_PAYLOAD support to CMD_BLOCK_STATUS

Allow a client to request a subset of negotiated meta contexts. For example, a client may ask to use a single connection to learn about both block status and dirty bitmaps, but where the dirty bitmap queries only need to be performed on a subset of the disk; forcing the server to compute that information on block status queries in the rest of the disk is wasted effort (both at the server, and on the amount of traffic sent over the wire to be parsed and ignored by the client). Qemu as an NBD client never requests to use more than one meta context, so it has no need to use block status payloads. Testing this instead requires support from libnbd, which CAN access multiple meta contexts in parallel from a single NBD connection; an interop test submitted to the libnbd project at the same time as this patch demonstrates the feature working, as well as testing some corner cases (for example, when the payload length is longer than the export length), although other corner cases (like passing the same id duplicated) requires a protocol fuzzer because libnbd is not wired up to break the protocol that badly. This also includes tweaks to 'qemu-nbd --list' to show when a server is advertising the capability, and to the testsuite to reflect the addition to that output. Of note: qemu will always advertise the new feature bit during NBD_OPT_INFO if extended headers have alreay been negotiated (regardless of whether any NBD_OPT_SET_META_CONTEXT negotiation has occurred); but for NBD_OPT_GO, qemu only advertises the feature if block status is also enabled (that is, if the client does not negotiate any contexts, then NBD_CMD_BLOCK_STATUS cannot be used, so the feature is not advertised). Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- v5: factor out 'id - NBD_MTA_ID_DIRTY_BITMAP' [Vladimir], rework logic on zero-length requests to be clearer [Vladimir], rebase to earlier changes

+/* + * nbd_co_block_status_payload_read + * Called when a client wants a subset of negotiated contexts via a + * BLOCK_STATUS payload. Check the payload for valid length and + * contents. On success, return 0 with request updated to effective + * length. If request was invalid but all payload consumed, return 0 + * with request->len and request->contexts->count set to 0 (which will + * trigger an appropriate NBD_EINVAL response later on). Return + * negative errno if the payload was not fully consumed. + */ +static int +nbd_co_block_status_payload_read(NBDClient *client, NBDRequest *request, + Error **errp) +{ + int payload_len = request->len;

+ g_autofree char *buf = NULL; + size_t count, i, nr_bitmaps; + uint32_t id; +

+ if (payload_len > NBD_MAX_BUFFER_SIZE) { + error_setg(errp, "len (%" PRIu64 ") is larger than max len (%u)", + request->len, NBD_MAX_BUFFER_SIZE); + return -EINVAL; + } + + assert(client->contexts.exp == client->exp); + nr_bitmaps = client->exp->nr_export_bitmaps; + request->contexts = g_new0(NBDMetaContexts, 1); + request->contexts->exp = client->exp; + + if (payload_len % sizeof(uint32_t) || + payload_len < sizeof(NBDBlockStatusPayload) || + payload_len > (sizeof(NBDBlockStatusPayload) + + sizeof(id) * client->contexts.count)) { + goto skip; + }

* connection right away, -EAGAIN to indicate we were interrupted and the @@ -2505,7 +2593,18 @@ static int coroutine_fn nbd_co_receive_request(NBDRequestData *req, break; case NBD_CMD_BLOCK_STATUS: - request->contexts = &client->contexts; + if (extended_with_payload) { + ret = nbd_co_block_status_payload_read(client, request, errp); + if (ret < 0) { + return ret; + } + /* payload now consumed */ + check_length = extended_with_payload = false;

+ payload_len = 0; + valid_flags |= NBD_CMD_FLAG_PAYLOAD_LEN; + } else { + request->contexts = &client->contexts; + } valid_flags |= NBD_CMD_FLAG_REQ_ONE; break;