[Nbd] [PATCH 1/3] NBD proto: forbid TRIM command without negotiation

["Denis V. Lunev" <den@...2317...>]

From: Pavel Borzenkov <pborzenkov@...2319...>

There is a loophole in the protocol that allows a client to send TRIM
request even if support for it wasn't negotiated with the server. State
explicitly that the client MUST NOT send such command without prior
successful negotiation.

Signed-off-by: Pavel Borzenkov <pborzenkov@...2319...>
Reviewed-by: Roman Kagan <rkagan@...2319...>
Signed-off-by: Denis V. Lunev <den@...2317...>
CC: Wouter Verhelst <w@...112...>
CC: Eric Blake <eblake@...696...>
CC: Alex Bligh <alex@...872...>
---
 doc/proto.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/doc/proto.md b/doc/proto.md
index 6d1cb34..d54ed19 100644
--- a/doc/proto.md
+++ b/doc/proto.md
@@ -471,6 +471,9 @@ The following request types exist:
     about the contents of the export affected by this command, until
     overwriting it again with `NBD_CMD_WRITE`.
 
+    A client MUST NOT send a trim request unless `NBD_FLAG_SEND_TRIM`
+    was set in the export flags field.
+
 * Other requests
 
     Some third-party implementations may require additional protocol
-- 
2.1.4