nbd_get_tls_negotiated - find out if TLS was negotiated on a connection


 #include <libnbd.h>

 int nbd_get_tls_negotiated (
       struct nbd_handle *h


After connecting you may call this to find out if the connection is using TLS.

This is normally useful only if you set the TLS request mode to LIBNBD_TLS_ALLOW (see nbd_set_tls(3)), because in this mode we try to use TLS but fall back to unencrypted if it was not available. This function will tell you if TLS was negotiated or not.

In LIBNBD_TLS_REQUIRE mode (the most secure) the connection would have failed if TLS could not be negotiated. With LIBNBD_TLS_DISABLE mode, TLS is not tried automatically; but if the NBD server uses the less-common SELECTIVETLS mode, this function reports whether a manual nbd_opt_starttls(3) enabled TLS or if the connection is still plaintext.


This call returns a boolean value.


On error -1 is returned.

Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

The following parameters must not be NULL: h. For more information see "Non-NULL parameters" in libnbd(3).


nbd_get_tls_negotiated can be called when the handle is in the following states:

 │ Handle created, before connecting   │ ❌ error                │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
 │ Connected to the server             │ ✅ allowed              │
 │ Connection shut down                │ ✅ allowed              │
 │ Handle dead                         │ ❌ error                │


This function first appeared in libnbd 1.2.

If you need to test if this function is available at compile time check if the following macro is defined:



nbd_create(3), nbd_get_tls(3), nbd_opt_starttls(3), nbd_set_tls(3), libnbd(3).


Eric Blake

Richard W.M. Jones


Copyright Red Hat


This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

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