NAME

       nbd_set_strict_mode - control how strictly to follow NBD protocol

SYNOPSIS

        #include <libnbd.h>

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

DESCRIPTION

       By default, libnbd tries to detect requests that would trigger undefined behavior in the
       NBD protocol, and rejects them client side without causing any network traffic, rather
       than risking undefined server behavior.  However, for integration testing, it can be handy
       to relax the strictness of libnbd, to coerce it into sending such requests over the
       network for testing the robustness of the server in dealing with such traffic.

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

       "LIBNBD_STRICT_COMMANDS" = 1
           If set, this flag rejects client requests that do not comply with the set of
           advertised server flags (for example, attempting a write on a read-only server, or
           attempting to use "LIBNBD_CMD_FLAG_FUA" when nbd_can_fua(3) returned false).  If
           clear, this flag relies on the server to reject unexpected commands.

       "LIBNBD_STRICT_FLAGS" = 2
           If set, this flag rejects client requests that attempt to set a command flag not
           recognized by libnbd (those outside of "LIBNBD_CMD_FLAG_MASK"), or a flag not normally
           associated with a command (such as using "LIBNBD_CMD_FLAG_FUA" on a read command).  If
           clear, all flags are sent on to the server, even if sending such a flag may cause the
           server to change its reply in a manner that confuses libnbd, perhaps causing deadlock
           or ending the connection.

           Flags that are known by libnbd as associated with a given command (such as
           "LIBNBD_CMD_FLAG_DF" for nbd_pread_structured(3) gated by nbd_can_df(3)) are
           controlled by "LIBNBD_STRICT_COMMANDS" instead.

           Note that the NBD protocol only supports 16 bits of command flags, even though the
           libnbd API uses "uint32_t"; bits outside of the range permitted by the protocol are
           always a client-side error.

       "LIBNBD_STRICT_BOUNDS" = 3
           If set, this flag rejects client requests that would exceed the export bounds without
           sending any traffic to the server.  If clear, this flag relies on the server to detect
           out-of-bounds requests.

       "LIBNBD_STRICT_ZERO_SIZE" = 4
           If set, this flag rejects client requests with length 0.  If clear, this permits zero-
           length requests to the server, which may produce undefined results.

       "LIBNBD_STRICT_ALIGN" = 5
           If set, and the server provided minimum block sizes (see nbd_get_block_size(3), this
           flag rejects client requests that do not have length and offset aligned to the
           server's minimum requirements.  If clear, unaligned requests are sent to the server,
           where it is up to the server whether to honor or reject the request.

       For convenience, the constant "LIBNBD_STRICT_MASK" is available to describe all strictness
       flags supported by this build of libnbd.  Future versions of libnbd may add further flags,
       which are likely to be enabled by default for additional client-side filtering.  As such,
       when attempting to relax only one specific bit while keeping remaining checks at the
       client side, it is wiser to first call nbd_get_strict_mode(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.

VERSION

       This function first appeared in libnbd 1.6.

       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_STRICT_MODE 1

SEE ALSO

       nbd_can_df(3), nbd_can_fua(3), nbd_create(3), nbd_get_block_size(3),
       nbd_get_strict_mode(3), nbd_pread_structured(3), nbd_set_handshake_flags(3), libnbd(3).

AUTHORS

       Eric Blake

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2019-2021 Red Hat Inc.

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