[Libguestfs] [nbdkit PATCH 1/5] protocol: Support NBD_FLAG_NO_ZEROES
The upstream NBD protocol allows a reduction in the length of the
handshake by both sides agreeing to skip the 124 bytes of padding
in the final server reply.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
src/connections.c | 14 +++++++++++---
src/protocol.h | 1 +
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/src/connections.c b/src/connections.c
index 840e315..16c6584 100644
--- a/src/connections.c
+++ b/src/connections.c
@@ -42,6 +42,7 @@
#include <errno.h>
#include <endian.h>
#include <sys/types.h>
+#include <stddef.h>
#include <pthread.h>
@@ -390,7 +391,7 @@ _negotiate_handshake_newstyle (struct connection *conn)
uint16_t eflags;
int fl;
- gflags = NBD_FLAG_FIXED_NEWSTYLE;
+ gflags = NBD_FLAG_FIXED_NEWSTYLE | NBD_FLAG_NO_ZEROES;
debug ("newstyle negotiation: flags: global 0x%x", gflags);
@@ -409,8 +410,12 @@ _negotiate_handshake_newstyle (struct connection *conn)
return -1;
}
cflags = be32toh (cflags);
- /* ... which other than printing out, we ignore. */
+ /* ... which we check for accuracy. */
debug ("newstyle negotiation: client flags: 0x%x", cflags);
+ if (cflags & ~gflags) {
+ nbdkit_error ("client requested unknown flags 0x%x", cflags);
+ return -1;
+ }
/* Receive newstyle options. */
if (_negotiate_handshake_newstyle_options (conn) == -1)
@@ -469,7 +474,10 @@ _negotiate_handshake_newstyle (struct connection *conn)
handshake_finish.eflags = htobe16 (eflags);
if (xwrite (conn->sockout,
- &handshake_finish, sizeof handshake_finish) == -1) {
+ &handshake_finish,
+ (cflags & NBD_FLAG_NO_ZEROES)
+ ? offsetof (struct new_handshake_finish, zeroes)
+ : sizeof handshake_finish) == -1) {
nbdkit_error ("write: %m");
return -1;
}
diff --git a/src/protocol.h b/src/protocol.h
index c885d9e..23630a9 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -84,6 +84,7 @@ struct new_handshake_finish {
/* Global flags. */
#define NBD_FLAG_FIXED_NEWSTYLE 1
+#define NBD_FLAG_NO_ZEROES 2
/* Per-export flags. */
#define NBD_FLAG_HAS_FLAGS 1
--
2.9.3