doc: Clarify use of EOVERFLOW

The error EOVERFLOW was added as part of the NBD_CMD_FLAG_DF flag for
structured reads. Since NBD errors are not necessarily 1:1 with local
errno values, it is conceivable that a client may not be expecting to
receive this value, so it is better to document that a server should
not send it in situations that older clients were not expecting.

Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/doc/proto.md b/doc/proto.md
index 8aaad96..e446f75 100644 (file)
--- a/doc/proto.md
+++ b/doc/proto.md
@@ -2125,6 +2125,9 @@ request is not aligned to advertised minimum block sizes. Finally, it
 SHOULD return `EPERM` if it receives a write or trim request on a
 read-only export.
 
+The server SHOULD NOT return `EOVERFLOW` except as documented in
+response to `NBD_CMD_READ` when `NBD_CMD_FLAG_DF` is supported.
+
 The server SHOULD return `EINVAL` if it receives an unknown command.
 
 The server SHOULD return `EINVAL` if it receives an unknown command flag. It