The NBD spec is proposing a relaxation of NBD_CMD_BLOCK_STATUS
where a server may have the final extent per context give a
length beyond the original request, if it can easily prove that
subsequent bytes have the same status, on the grounds that a
client can take advantage of this information for fewer block
status requests. Since qemu 2.12 as a client always sends
NBD_CMD_FLAG_REQ_ONE, and rejects a server that sends extra
length, the upstream NBD spec will probably limit this behavior
to clients that don't request REQ_ONE semantics; but it doesn't
hurt to relax qemu to always be permissive of this server
behavior, even if it continues to use REQ_ONE.
Signed-off-by: Eric Blake <address@hidden>
---
block/nbd-client.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/block/nbd-client.c b/block/nbd-client.c
index e7caf49fbb4..25d34631fe7 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -259,14 +259,18 @@ static int nbd_parse_blockstatus_payload(NBDClientSession
*client,
if (extent->length == 0 ||
(client->info.min_block && !QEMU_IS_ALIGNED(extent->length,
- client->info.min_block)) ||
- extent->length > orig_length)
- {
+ client->info.min_block))) {
error_setg(errp, "Protocol error: server sent status chunk with "
"invalid length");
return -EINVAL;
}
+ /* The server is allowed to send us extra information on the final
+ * extent; just clamp it to the length we requested. */
+ if (extent->length > orig_length) {
+ extent->length == orig_length;
+ }
+
return 0;
}