nbd_set_strict_mode - control how strictly to follow NBD protocol

       Eric Blake

       Richard W.M. Jones

       Copyright Red Hat

       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" = 0x1
           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" = 0x2
           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;
           and "LIBNBD_CMD_FLAG_PAYLOAD_LEN" is managed automatically by libnbd unless "LIBNBD_STRICT_AUTO_FLAG"
           is disabled.

           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" = 0x4
           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" = 0x8
           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" = 0x10
           If   set,   and   the   server   provided   minimum   block   sizes  (see  "LIBNBD_SIZE_MINIMUM"  for
           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.

       "LIBNBD_STRICT_PAYLOAD" = 0x20
           If set, the client refuses to send a command to the server with more than libnbd's  outgoing  payload
           maximum (see "LIBNBD_SIZE_PAYLOAD" for nbd_get_block_size(3)), whether or not the server advertised a
           block  size  maximum.   If  clear,  oversize requests up to 64MiB may be attempted, although requests
           larger than 32MiB are liable to cause some servers to disconnect.

       "LIBNBD_STRICT_AUTO_FLAG" = 0x40
           If set, commands that accept  the  "LIBNBD_CMD_FLAG_PAYLOAD_LEN"  flag  (such  as  nbd_pwrite(3)  and
           nbd_block_status_filter(3))  ignore  the  presence  or  absence of that flag from the caller, instead
           sending the value over the wire that matches the server's  expectations  based  on  whether  extended
           headers  were  negotiated  when  the  connection  was  made.   If  clear,  the  caller  takes  on the
           responsibility for whether the payload length flag is set or clear during the affected command, which
           can be useful during integration testing but is more likely to lead to undefined behavior.

       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.

       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).

       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

libnbd-1.22.2                                      2025-06-16                             nbd_set_strict_mode(3)

       nbd_set_strict_mode - control how strictly to follow NBD protocol

       If the call is successful the function returns 0.

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_pwrite(3),    nbd_set_handshake_flags(3),    nbd_stats_bytes_received(3),
       nbd_stats_bytes_sent(3), libnbd(3).

        #include <libnbd.h>

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

       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