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.\" ========================================================================
.\"
.IX Title "nbd_set_strict_mode 3"
.TH nbd_set_strict_mode 3 "2021-02-09" "libnbd-1.6.1" "LIBNBD"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
nbd_set_strict_mode \- control how strictly to follow NBD protocol
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <libnbd.h>
\&
\& int nbd_set_strict_mode (struct nbd_handle *h,
\&                          uint32_t flags);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
By default, libnbd tries to detect requests that would trigger
undefined behavior in the \s-1NBD\s0 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.
.PP
The \f(CW\*(C`flags\*(C'\fR argument is a bitmask, including zero or more of the
following strictness flags:
.ie n .IP """LIBNBD_STRICT_COMMANDS"" = 1" 4
.el .IP "\f(CWLIBNBD_STRICT_COMMANDS\fR = 1" 4
.IX Item "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 \f(CW\*(C`LIBNBD_CMD_FLAG_FUA\*(C'\fR when
\&\fBnbd_can_fua\fR\|(3) returned false).  If clear, this flag relies on the
server to reject unexpected commands.
.ie n .IP """LIBNBD_STRICT_FLAGS"" = 2" 4
.el .IP "\f(CWLIBNBD_STRICT_FLAGS\fR = 2" 4
.IX Item "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
\&\f(CW\*(C`LIBNBD_CMD_FLAG_MASK\*(C'\fR), or a flag not normally associated with
a command (such as using \f(CW\*(C`LIBNBD_CMD_FLAG_FUA\*(C'\fR 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.
.Sp
Flags that are known by libnbd as associated with a given command
(such as \f(CW\*(C`LIBNBD_CMD_FLAG_DF\*(C'\fR for \fBnbd_pread_structured\fR\|(3) gated
by \fBnbd_can_df\fR\|(3)) are controlled by \f(CW\*(C`LIBNBD_STRICT_COMMANDS\*(C'\fR
instead.
.Sp
Note that the \s-1NBD\s0 protocol only supports 16 bits of command flags,
even though the libnbd \s-1API\s0 uses \f(CW\*(C`uint32_t\*(C'\fR; bits outside of the
range permitted by the protocol are always a client-side error.
.ie n .IP """LIBNBD_STRICT_BOUNDS"" = 3" 4
.el .IP "\f(CWLIBNBD_STRICT_BOUNDS\fR = 3" 4
.IX Item "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.
.ie n .IP """LIBNBD_STRICT_ZERO_SIZE"" = 4" 4
.el .IP "\f(CWLIBNBD_STRICT_ZERO_SIZE\fR = 4" 4
.IX Item "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.
.ie n .IP """LIBNBD_STRICT_ALIGN"" = 5" 4
.el .IP "\f(CWLIBNBD_STRICT_ALIGN\fR = 5" 4
.IX Item "LIBNBD_STRICT_ALIGN = 5"
If set, and the server provided minimum block sizes (see
\&\fBnbd_get_block_size\fR\|(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.
.PP
For convenience, the constant \f(CW\*(C`LIBNBD_STRICT_MASK\*(C'\fR 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
\&\fBnbd_get_strict_mode\fR\|(3) and modify that value, rather than
blindly setting a constant value.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
If the call is successful the function returns \f(CW0\fR.
.SH "ERRORS"
.IX Header "ERRORS"
On error \f(CW\*(C`\-1\*(C'\fR is returned.
.PP
Refer to \*(L"\s-1ERROR HANDLING\*(R"\s0 in \fBlibnbd\fR\|(3)
for how to get further details of the error.
.SH "VERSION"
.IX Header "VERSION"
This function first appeared in libnbd 1.6.
.PP
If you need to test if this function is available at compile time
check if the following macro is defined:
.PP
.Vb 1
\& #define LIBNBD_HAVE_NBD_SET_STRICT_MODE 1
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbd_can_df\fR\|(3),
\&\fBnbd_can_fua\fR\|(3),
\&\fBnbd_create\fR\|(3),
\&\fBnbd_get_block_size\fR\|(3),
\&\fBnbd_get_strict_mode\fR\|(3),
\&\fBnbd_pread_structured\fR\|(3),
\&\fBnbd_set_handshake_flags\fR\|(3),
\&\fBlibnbd\fR\|(3).
.SH "AUTHORS"
.IX Header "AUTHORS"
Eric Blake
.PP
Richard W.M. Jones
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 2019\-2020 Red Hat Inc.
.SH "LICENSE"
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or
modify it under the terms of the \s-1GNU\s0 Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
.PP
This library is distributed in the hope that it will be useful,
but \s-1WITHOUT ANY WARRANTY\s0; without even the implied warranty of
\&\s-1MERCHANTABILITY\s0 or \s-1FITNESS FOR A PARTICULAR PURPOSE.\s0  See the \s-1GNU\s0
Lesser General Public License for more details.
.PP
You should have received a copy of the \s-1GNU\s0 Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, \s-1MA 02110\-1301 USA\s0