1nbd_set_strict_mode(3) LIBNBD nbd_set_strict_mode(3)
2
6 nbd_set_strict_mode - control how strictly to follow NBD protocol
7
9 #include <libnbd.h>
10 int nbd_set_strict_mode (
12 struct nbd_handle *h, uint32_t flags
13 );
14
16 By default, libnbd tries to detect requests that would trigger
17 undefined behavior in the NBD protocol, and rejects them client side
18 without causing any network traffic, rather than risking undefined
19 server behavior. However, for integration testing, it can be handy to
20 relax the strictness of libnbd, to coerce it into sending such requests
21 over the network for testing the robustness of the server in dealing
22 with such traffic.
23 The "flags" argument is a bitmask, including zero or more of the
25 following strictness flags:
26 "LIBNBD_STRICT_COMMANDS" = 0x1
28 If set, this flag rejects client requests that do not comply with
29 the set of advertised server flags (for example, attempting a write
30 on a read-only server, or attempting to use "LIBNBD_CMD_FLAG_FUA"
31 when nbd_can_fua(3) returned false). If clear, this flag relies on
32 the server to reject unexpected commands.
33 "LIBNBD_STRICT_FLAGS" = 0x2
35 If set, this flag rejects client requests that attempt to set a
36 command flag not recognized by libnbd (those outside of
37 "LIBNBD_CMD_FLAG_MASK"), or a flag not normally associated with a
38 command (such as using "LIBNBD_CMD_FLAG_FUA" on a read command).
39 If clear, all flags are sent on to the server, even if sending such
40 a flag may cause the server to change its reply in a manner that
41 confuses libnbd, perhaps causing deadlock or ending the connection.
42 Flags that are known by libnbd as associated with a given command
44 (such as "LIBNBD_CMD_FLAG_DF" for nbd_pread_structured(3) gated by
45 nbd_can_df(3)) are controlled by "LIBNBD_STRICT_COMMANDS" instead.
46 Note that the NBD protocol only supports 16 bits of command flags,
48 even though the libnbd API uses "uint32_t"; bits outside of the
49 range permitted by the protocol are always a client-side error.
50 "LIBNBD_STRICT_BOUNDS" = 0x4
52 If set, this flag rejects client requests that would exceed the
53 export bounds without sending any traffic to the server. If clear,
54 this flag relies on the server to detect out-of-bounds requests.
55 "LIBNBD_STRICT_ZERO_SIZE" = 0x8
57 If set, this flag rejects client requests with length 0. If clear,
58 this permits zero-length requests to the server, which may produce
59 undefined results.
60 "LIBNBD_STRICT_ALIGN" = 0x10
62 If set, and the server provided minimum block sizes (see
63 "LIBNBD_SIZE_MINIMUM" for nbd_get_block_size(3)), this flag rejects
64 client requests that do not have length and offset aligned to the
65 server's minimum requirements. If clear, unaligned requests are
66 sent to the server, where it is up to the server whether to honor
67 or reject the request.
68 "LIBNBD_STRICT_PAYLOAD" = 0x20
70 If set, the client refuses to send a command to the server with
71 more than libnbd's outgoing payload maximum (see
72 "LIBNBD_SIZE_PAYLOAD" for nbd_get_block_size(3)), whether or not
73 the server advertised a block size maximum. If clear, oversize
74 requests up to 64MiB may be attempted, although requests larger
75 than 32MiB are liable to cause some servers to disconnect.
76 For convenience, the constant "LIBNBD_STRICT_MASK" is available to
78 describe all strictness flags supported by this build of libnbd.
79 Future versions of libnbd may add further flags, which are likely to be
80 enabled by default for additional client-side filtering. As such, when
81 attempting to relax only one specific bit while keeping remaining
82 checks at the client side, it is wiser to first call
83 nbd_get_strict_mode(3) and modify that value, rather than blindly
84 setting a constant value.
85
87 If the call is successful the function returns 0.
88
90 On error -1 is returned.
91 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
93 of the error.
94 The following parameters must not be NULL: "h". For more information
96 see "Non-NULL parameters" in libnbd(3).
97
99 This function first appeared in libnbd 1.6.
100 If you need to test if this function is available at compile time check
102 if the following macro is defined:
103 #define LIBNBD_HAVE_NBD_SET_STRICT_MODE 1
105
107 nbd_can_df(3), nbd_can_fua(3), nbd_create(3), nbd_get_block_size(3),
108 nbd_get_strict_mode(3), nbd_pread_structured(3),
109 nbd_set_handshake_flags(3), nbd_stats_bytes_received(3),
110 nbd_stats_bytes_sent(3), libnbd(3).
111
113 Eric Blake
114 Richard W.M. Jones
116
118 Copyright Red Hat
119
121 This library is free software; you can redistribute it and/or modify it
122 under the terms of the GNU Lesser General Public License as published
123 by the Free Software Foundation; either version 2 of the License, or
124 (at your option) any later version.
125 This library is distributed in the hope that it will be useful, but
127 WITHOUT ANY WARRANTY; without even the implied warranty of
128 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
129 Lesser General Public License for more details.
130 You should have received a copy of the GNU Lesser General Public
132 License along with this library; if not, write to the Free Software
133 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
134 02110-1301 USA
135libnbd-1.16.5 2023-09-26 nbd_set_strict_mode(3)