nbd_get_protocol3

Usage

 #include <libnbd.h>
 const char * nbd_get_protocol (
                struct nbd_handle *h
              );

Overview

Return the NBD protocol variant in use on the connection. At the moment this returns one of the strings "oldstyle", "newstyle" or "newstyle-fixed". Other strings might be returned in the future. Most modern NBD servers use "newstyle-fixed".

This call does not block, because it returns data that is saved in the handle from the NBD protocol handshake.

Return value

This call returns a statically allocated string, valid for the lifetime of the process or until libnbd is unloaded by dlclose(3). You must not try to free the string.

Errors

On error "NULL" 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).

Handle state

nbd_get_protocol 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                │
 └─────────────────────────────────────┴─────────────────────────┘

Version

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:

 #define LIBNBD_HAVE_NBD_GET_PROTOCOL 1