NAME

       nbd_set_handshake_flags - control use of handshake flags

SYNOPSIS

        #include <libnbd.h>

        int nbd_set_handshake_flags (
              struct nbd_handle *h, uint32_t flags
            );

DESCRIPTION

       By default, libnbd tries to negotiate all possible handshake flags that are also supported
       by the server, since omitting a handshake flag can prevent the use of other functionality
       such as TLS encryption or structured replies.  However, for integration testing, it can be
       useful to reduce the set of flags supported by the client to test that a particular server
       can handle various clients that were compliant to older versions of the NBD specification.

       The "flags" argument is a bitmask, including zero or more of the following handshake
       flags:

       "LIBNBD_HANDSHAKE_FLAG_FIXED_NEWSTYLE" = 1
           The server gracefully handles unknown option requests from the client, rather than
           disconnecting.  Without this flag, a client cannot safely request to use extensions
           such as TLS encryption or structured replies, as the request may cause an older server
           to drop the connection.

       "LIBNBD_HANDSHAKE_FLAG_NO_ZEROES" = 2
           If the client is forced to use "NBD_OPT_EXPORT_NAME" instead of the preferred
           "NBD_OPT_GO", this flag allows the server to send fewer all-zero padding bytes over
           the connection.

       For convenience, the constant "LIBNBD_HANDSHAKE_FLAG_MASK" is available to describe all
       flags supported by this build of libnbd.  Future NBD extensions may add further flags,
       which in turn may be enabled by default in newer libnbd.  As such, when attempting to
       disable only one specific bit, it is wiser to first call nbd_get_handshake_flags(3) and
       modify that value, rather than blindly setting a constant value.

RETURN VALUE

       If the call is successful the function returns 0.

ERRORS

       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).

HANDLE STATE

       nbd_set_handshake_flags can be called when the handle is in the following state:

        ┌─────────────────────────────────────┬─────────────────────────┐
        │ Handle created, before connecting   │ ✅ allowed              │
        │ Connecting                          │ ❌ error                │
        │ Connecting & handshaking (opt_mode) │ ❌ error                │
        │ Connected to the server             │ ❌ error                │
        │ Connection shut down                │ ❌ error                │
        │ 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_SET_HANDSHAKE_FLAGS 1

SEE ALSO

       nbd_create(3), nbd_get_handshake_flags(3), nbd_set_request_structured_replies(3),
       libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright Red Hat

LICENSE

       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.

       You should have received a copy of the GNU Lesser General Public License along with this
       library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth
       Floor, Boston, MA 02110-1301 USA