On 08.06.23 16:56, Eric Blake wrote:
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.
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
[..]
+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;
+
+ assert(request->len <= NBD_MAX_BUFFER_SIZE);
+ 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;
+ }
+
+ buf = g_malloc(payload_len);
+ if (nbd_read(client->ioc, buf, payload_len,
+ "CMD_BLOCK_STATUS data", errp) < 0) {
+ return -EIO;
+ }
+ trace_nbd_co_receive_request_payload_received(request->cookie,
+ payload_len);
+ request->contexts->bitmaps = g_new0(bool, nr_bitmaps);
+ count = (payload_len - sizeof(NBDBlockStatusPayload)) / sizeof(id);
+ payload_len = 0;
+
+ for (i = 0; i < count; i++) {
+ id = ldl_be_p(buf + sizeof(NBDBlockStatusPayload) + sizeof(id) * i);
+ if (id == NBD_META_ID_BASE_ALLOCATION) {
+ if (request->contexts->base_allocation) {
+ goto skip;
+ }
+ request->contexts->base_allocation = true;
+ } else if (id == NBD_META_ID_ALLOCATION_DEPTH) {
+ if (request->contexts->allocation_depth) {
+ goto skip;
+ }
+ request->contexts->allocation_depth = true;
+ } else {
maybe,
int ind = id - NBD_META_ID_DIRTY_BITMAP;
+ if (id - NBD_META_ID_DIRTY_BITMAP > nr_bitmaps ||
= ?
+ request->contexts->bitmaps[id - NBD_META_ID_DIRTY_BITMAP]) {
+ goto skip;
+ }
+ request->contexts->bitmaps[id - NBD_META_ID_DIRTY_BITMAP] = true;
+ }
+ }
+
+ request->len = ldq_be_p(buf);
+ request->contexts->count = count;
+ return 0;
+
+ skip:
+ trace_nbd_co_receive_block_status_payload_compliance(request->from,
+ request->len);
+ request->len = request->contexts->count = 0;
+ return nbd_drop(client->ioc, payload_len, errp);
+}
+
/* nbd_co_receive_request
* Collect a client request. Return 0 if request looks valid, -EIO to drop
* connection right away, -EAGAIN to indicate we were interrupted and the
@@ -2470,7 +2552,13 @@ static int coroutine_fn
nbd_co_receive_request(NBDRequestData *req, NBDRequest *
[..]
@@ -2712,7 +2804,8 @@ static coroutine_fn int nbd_handle_request(NBDClient
*client,
"discard failed", errp);
case NBD_CMD_BLOCK_STATUS:
- if (!request->len) {
+ assert(request->contexts);
+ if (!request->len && !(request->flags & NBD_CMD_FLAG_PAYLOAD_LEN)) {
why not error-out for len=0 in case of payload?
return nbd_send_generic_reply(client, request, -EINVAL,
"need non-zero length", errp);
}
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 1d155fc2c66..cbca0eeee62 100644
--
Best regards,
Vladimir
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