1nbd_opt_starttls(3)                 LIBNBD                 nbd_opt_starttls(3)
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NAME

6       nbd_opt_starttls - request the server to initiate TLS
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SYNOPSIS

9        #include <libnbd.h>
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11        int nbd_opt_starttls (
12              struct nbd_handle *h
13            );
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DESCRIPTION

16       Request that the server initiate a secure TLS connection, by sending
17       "NBD_OPT_STARTTLS".  This can only be used if nbd_set_opt_mode(3)
18       enabled option mode; furthermore, if you use nbd_set_tls(3) to request
19       anything other than the default of "LIBNBD_TLS_DISABLE", then libnbd
20       will have already attempted a TLS connection prior to allowing you
21       control over option negotiation.  This command is disabled if
22       nbd_supports_tls(3) reports false.
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24       This function is mainly useful for integration testing of corner cases
25       in server handling; in particular, misuse of this function when coupled
26       with a server that is not careful about resetting stateful commands
27       such as nbd_opt_structured_reply(3) could result in a security hole
28       (see CVE-2021-3716 against nbdkit, for example).  Thus, when security
29       is a concern, you should instead prefer to use nbd_set_tls(3) with
30       "LIBNBD_TLS_REQUIRE" and let libnbd negotiate TLS automatically.
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32       This function returns true if the server replies with success, false if
33       the server replies with an error, and fails only if the server does not
34       reply (such as for a loss of connection, which can include when the
35       server rejects credentials supplied during the TLS handshake).  Note
36       that the NBD protocol documents that requesting TLS after it is already
37       enabled is a client error; most servers will gracefully fail a second
38       request, but that does not downgrade a TLS session that has already
39       been established, as reported by nbd_get_tls_negotiated(3).
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RETURN VALUE

42       This call returns a boolean value.
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ERRORS

45       On error -1 is returned.
46
47       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
48       of the error.
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50       The following parameters must not be NULL: "h".  For more information
51       see "Non-NULL parameters" in libnbd(3).
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HANDLE STATE

54       The handle must be negotiating, otherwise this call will return an
55       error.
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VERSION

58       This function first appeared in libnbd 1.16.
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60       If you need to test if this function is available at compile time check
61       if the following macro is defined:
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63        #define LIBNBD_HAVE_NBD_OPT_STARTTLS 1
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SEE ALSO

66       nbd_aio_opt_starttls(3), nbd_create(3), nbd_get_tls_negotiated(3),
67       nbd_opt_structured_reply(3), nbd_set_opt_mode(3), nbd_set_tls(3),
68       nbd_supports_tls(3), libnbd(3).
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AUTHORS

71       Eric Blake
72
73       Richard W.M. Jones
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76       Copyright Red Hat
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LICENSE

79       This library is free software; you can redistribute it and/or modify it
80       under the terms of the GNU Lesser General Public License as published
81       by the Free Software Foundation; either version 2 of the License, or
82       (at your option) any later version.
83
84       This library is distributed in the hope that it will be useful, but
85       WITHOUT ANY WARRANTY; without even the implied warranty of
86       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
87       Lesser General Public License for more details.
88
89       You should have received a copy of the GNU Lesser General Public
90       License along with this library; if not, write to the Free Software
91       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
92       02110-1301 USA
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96libnbd-1.16.5                     2023-09-26               nbd_opt_starttls(3)
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